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19-1054; Rev 0; 1/08
KIT ATION EVALU LE B AVAILA
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
General Description
The MAX16816 is a current-mode, high-brightness LED (HB LED) driver designed to control two external n-channel MOSFETs for single-string LED current regulation. The MAX16816 integrates all the building blocks necessary to implement fixed-frequency HB LED drivers with wide-range dimming control and EEPROMprogrammable LED current binning with a factor of up to 1.6. This device is configurable to operate as a stepdown (buck), step-up (boost), or step-up/step-down (buck-boost) current regulator. Current-mode control with adjustable leading-edge blanking simplifies control-loop design. Adjustable slope compensation stabilizes the current loop when operating at duty cycles above 50%. The MAX16816 operates over a wide input voltage range and is capable of withstanding automotive load-dump events. Multiple MAX16816 devices can be synchronized to each other or to an external clock. The MAX16816 includes a floating dimming driver for brightness control with an external n-channel MOSFET in series with the LED string. HB LEDs using the MAX16816 can achieve efficiencies of over 90% in automotive applications. The MAX16816 also includes a 1.4A source and 2A sink gate driver for driving switching MOSFETs in high-power LED driver applications, such as front light assemblies. Dimming control allows for wide PWM dimming range at frequencies up to 5kHz. Higher dimming ratios (up to 1000:1) are achievable at lower dimming frequencies. The MAX16816 provides user-programmable features through on-chip nonvolatile EEPROM registers. Adjustable features include a programmable soft-start, LED current (binning), external MOSFET gate driver supply voltage, slope compensation, leading-edge blanking time, and disabling/enabling of the RT oscillator. The MAX16816 is available in a 32-pin TQFN package with exposed pad and operates over the -40C to +125C automotive temperature range.
Features
o EEPROM-Programmable LED Current Binning o Wide Input Range: 5.9V to 76V with Cold Start Operation to 5.4V o Integrated Floating Differential LED CurrentSense Amplifier o Floating Dimming Driver Capable of Driving an n-Channel MOSFET o 5% or Better LED Current Accuracy o Multiple Topologies: Buck, Boost, Buck-Boost, SEPIC o Resistor-Programmable Switching Frequency (125kHz to 500kHz) and Synchronization Capability o 200Hz On-Board Ramp Allows Analog-Controlled PWM Dimming and External PWM Dimming o Output Overvoltage, Overcurrent, and LED Short Protection o Enable/Shutdown Input with Shutdown Current Below 45A
MAX16816
Ordering Information
PART TEMP RANGE PINPACKAGE 32 TQFN-EP* PKG CODE T3255M-4
MAX16816ATJ+ -40C to +125C
+Denotes a lead-free package. *EP = Exposed pad.
Pin Configuration appears at end of data sheet.
Typical Operating Circuits
VIN BUCK-BOOST CONFIGURATION RCS RUV2 CCLMP
RUV1 UVEN CUVEN
VCC
LO
CLMP
CS-
CS+
DGT RD DRV SNS+ QS LEDs RSENSE
Applications
Automotive Exterior: Rear Combination Lights (RCL), Daytime Running Lights (DRL), Fog and Front Lighting, High-Beam/Low-Beam/Turn Lights General Illumination Navigation and Marine Indicators Neon Replacement, Emergency Lighting Signage and Beacons
CREG1
DIM
DIM REG1
SNS-
MAX16816
QGND HI
RT RTSYNC
CF ROV1
FAULT OV COMP R1 CS FB AGND SGND REG2 DRI ROV2 CREG2
C2 C1 R2
Typical Operating Circuits continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming MAX16816
ABSOLUTE MAXIMUM RATINGS
VCC, HI, LO, CLMP to QGND .................................-0.3V to +80V CS+, CS-, DGT, UVEN, FAULT to QGND...............-0.3V to +80V UVEN to QGND ..........................................-0.3V to (VCC + 0.3V) DRV to SGND .........................................................-0.3V to +18V DRI, REG2, DIM to AGND ......................................-0.3V to +18V QGND, SGND to AGND ........................................-0.3V to +0.3V SNS+ to SNS- ...........................................................-0.3V to +6V CS, FB, COMP, SNS+, SNS-, OV, REF, RTSYNC to AGND ................................................-0.3V to +6V REG1, CLKOUT to AGND ........................................-0.3V to +6V CS+ to CS- .............................................................-0.3V to +12V HI to LO ..................................................................-0.3V to +36V CS+, CS-, DGT, CLMP to LO .................................-0.3V to +12V CS+, CS-, DGT, CLMP to LO ........................-0.3V to (HI + 0.3V) HI to CLMP .............................................................-0.3V to +28V Continuous Power Dissipation* (TA = +70C) 32-Pin TQFN (derate 34.5mW/C above +70C) .......2758mW Thermal Resistance JA ................................................................................29C/W JC ...............................................................................1.7C/W Operating Temperature Range .........................-40C to +125C Maximum Junction Temperature .....................................+150C Storage Temperature Range .............................-60C to +150C Lead Temperature (soldering, 10s) .................................+300C *As per JEDEC 51 standard, Multilayer Board (PCB).
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = VUVEN = 14V, CREG1 = 1F, CREG2 = 1F, CCLMP = 0.1F, RT = 25k, TA = TJ = -40C to +125C, unless otherwise noted. Typical specifications are at TA = +25C.)
PARAMETER Input Voltage Range Supply Current to VCC Supply Current to HI Shutdown Current to VCC Shutdown Current to HI UVEN VCC UVLO Threshold VCC Threshold Hysteresis UVEN Threshold UVEN Input Current REGULATORS REG1 Regulator Output REG1 Dropout Voltage REG1 Load Regulation REG2 Dropout Voltage REG2 Load Regulation V/I V/I VREG1 0 < IREG1 < 2mA, 7.5V < VCC < 76V IREG1 = 2mA, VCC = 5.7V IREG1 = 2mA (Note 1) VCC = 7.5V, IREG1 = 0 to 2mA VCC 9.5V, REG2 control register is `0011', IREG2 = 20mA (Note 1) VCC 9.5V, REG2 control register is `0011', IREG2 = 0 to 20mA 0.5 4.75 4.00 5.00 4.50 0.5 5.25 5.25 1.0 25 1.0 25 V V V VCC_R VCC_F VCC_HYS VUVR VUVF IUVEN VUVEN rising VUVEN falling (VUVEN = 0V and VCC = 14V) (VUVEN = 76V and VCC = 77V) 1.10 1.00 -0.2 VCC rising VCC falling 5.5 5.0 0.4 1.244 1.145 1.36 1.26 +0.2 6.0 5.5 V V V A SYMBOL VCC IQ_VCC IQ_HI ISHDN_VCC ISHDN_HI Exclude current to the gate driver, IREG2 VHI = 14V VUVEN 300mV VUVEN 300mV CONDITIONS MIN 5.5 2.7 0.5 25 1 TYP MAX 76 4.5 1.0 45 10 UNITS V mA mA A A
2
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
ELECTRICAL CHARACTERISTICS (continued)
(VCC = VUVEN = 14V, CREG1 = 1F, CREG2 = 1F, CCLMP = 0.1F, RT = 25k, TA = TJ = -40C to +125C, unless otherwise noted. Typical specifications are at TA = +25C.)
PARAMETER SYMBOL CONDITIONS REG2 control register is `0000', VCC 7.5V, IREG2 = 1mA REG2 control register is `0011', VCC 9.5V, IREG2 = 1mA REG2 control register is `1111', VCC 17.5V, IREG2 = 1mA REG2 control register is `0000', VCC = 5.7V, 0 IREG2 20mA REG2 control register is `0000', VCC = 7.5V, 0 IREG2 20mA REG2 control register is `1111', VCC = 17.5V, 0 IREG2 20mA HIGH-SIDE REGULATOR (CLMP) (All voltages referred to VLO) (Note 2) CLMP UVLO Threshold CLMP UVLO Threshold Hysteresis CLMP Regulator Output Voltage VCLMP_TH VCLMP_HYS 8.7V (VHI - VLO) 36V, ICLMP = 1mA VCLMP 5.0V (VHI - VLO) 8.7V, ICLMP = 250A 5.5 VCLMP rising 2.0 2.5 0.22 8.0 (VHI - VLO) - 0.7 10.0 V 3.0 V V MIN 4.75 6.65 13.5 4 4.75 13.5 TYP 5 7.0 15 4.5 5 15 MAX 5.25 7.35 16.5 V 5.25 5.25 16.5 UNITS
MAX16816
REG2 Regulation Voltage
CURRENT-SENSE AMPLIFIER (CSA) Differential Input Voltage Range Common-Mode Range CS+ Input Bias Current CS- Input Bias Current Unity-Gain Bandwidth REF OUTPUT BUFFER REF Output Voltage DIM DRIVER Minimal Pulse Width Source Current Sink Current GATE DRIVER DRI Voltage Range DRI UVLO Threshold DRI UVLO Threshold Hysteresis VDRI VUVLO_TH VUVLO_HYST VCC 2.5V above VDRI 5 4.0 4.2 0.3 15 4.4 V V V fDIM = 200Hz (Note 3) VCLMP - VLO = 4V VCLMP - VLO = 8V VCLMP - VLO = 4V VCLMP - VLO = 8V 5 30 10 40 20 20 67 22 76 40 s mA mA VREF -100A IL +100A 2.85 3.0 3.15 V ICS+ ICSVCS+ - VCSVCC 68V VCS+ = 0.3V, VCS- = 0V VCS+ = 0.3V, VCS- = 0V From (CS+ to CS-) to CS 1.0 0 0 -250 0.3 VCC +250 400 V V nA A MHz
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3
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming MAX16816
ELECTRICAL CHARACTERISTICS (continued)
(VCC = VUVEN = 14V, CREG1 = 1F, CREG2 = 1F, CCLMP = 0.1F, RT = 25k, TA = TJ = -40C to +125C, unless otherwise noted. Typical specifications are at TA = +25C.)
PARAMETER Driver Output Impedance Peak Sink Current Peak Source Current PWM Comparator Offset Voltage Peak Current-Limit Comparator Trip Threshold Peak Current-Limit Comparator Propagation Delay (Excluding Blanking Time) HICCUP Comparator Trip Threshold SNS+ Input Bias Current SNS- Input Bias Current BLANKING TIME Blanking Time Control Register is `00' Blanking Time Blanking Time Control Register is `01' Blanking Time Control Register is `10' Blanking Time Control Register is `11' ERROR AMPLIFIER FB Input Bias Current EAMP Output Sink Current EAMP Output Source Current EAMP Input Common-Mode Voltage EAMP Output Clamp Voltage Voltage Gain Unity-Gain Bandwidth AV GBW RCOMP = 100k to AGND RCOMP = 100k to AGND, CCOMP = 100pF to AGND VCOM VFB = 1V VFB = 1.735V, VCOMP = 1V VFB = 0.735V, VCOMP = 1V (Note 5) -100 3 2 0 1.3 2.0 80 0.5 7 7 1.6 2.7 +100 nA mA mA V V dB MHz 150 125 100 75 ns VSNS+ = 0V, VSNS- = 0V VSNS+ = 0V, VSNS- = 0V SYMBOL ZOUT_L ZOUT_H ISK ISR CONDITIONS VDRI = 7.0V, DRV sinking 250mA VDRI = 7.0V, DRV sourcing 250mA VDRI = 7.0V VDRI = 7.0V MIN TYP 2.8 5.0 2.5 1.4 MAX 4 8 UNITS A A
PWM, ILIM, AND HICCUP COMPARATOR VCOMP - (VSNS+ -VSNS-) 160 0.8 200 245 V mV
50mV overdrive
40
ns
235 -100 -100
300 -65 -65
385
mV A A
OSCILLATOR, OSC SYNC, CLK, AND CLKOUT SYNC Frequency Range RTSYNC Oscillator Frequency SYNC High-Level Voltage SYNC Low-Level Voltage VSIHL VSILL fSW_MIN fSW_MAX RTOF bit set to `0', RT = 100k RTOF bit set to `0', RT = 25k 500 106 475 2.8 0.4 125 500 143 525 125 kHz kHz V V
4
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
ELECTRICAL CHARACTERISTICS (continued)
(VCC = VUVEN = 14V, CREG1 = 1F, CREG2 = 1F, CCLMP = 0.1F, RT = 25k, TA = TJ = -40C to +125C, unless otherwise noted. Typical specifications are at TA = +25C.)
PARAMETER CLKOUT High Level CLKOUT Low Level CLKOUT Maximum Load Capacitance Internal RAMP Frequency External Sync Frequency Range External Sync Low-Level Voltage External Sync High-Level Voltage DIM Comparator Offset CCLK_CAP SYMBOL ISINK = 0.8mA ISOURCE = 1.6mA fSW = 500kHz CONDITIONS MIN 2.8 0.4 500 TYP MAX UNITS V V pF
MAX16816
DIM SYNC, DIM RAMP, AND DIM PWM GEN fRAMP fDIM VLTH VHTH VDIMOS Digital Soft-Start Duration register is `000' Digital Soft-Start Duration register is `001' Digital Soft-Start Duration register is `010' Soft-Start Duration tSS Digital Soft-Start Duration register is `011' Digital Soft-Start Duration register is `100' Digital Soft-Start Duration register is `101' Digital Soft-Start Duration register is `110' Digital Soft-Start Duration register is `111' Binning Adjustment register is `0000' Binning Adjustment register is `0001' Binning Adjustment register is `0010' Binning Adjustment register is `0011' Binning Adjustment register is `0100' Binning Range Binning Adjustment register is `0101' Binning Adjustment register is `0110' Binning Adjustment register is `0111' Binning Adjustment register is `1000' Binning Adjustment register is `1001' Binning Adjustment register is `1010' OVERVOLTAGE COMPARATOR, LOAD OVERCURRENT COMPARATOR OVP Overvoltage Comparator Threshold OVP Overvoltage Comparator Hysteresis VOV VOV_HYST VOV rising 1.20 1.235 63.5 1.27 V mV 3.2 170 200 4096 2048 1536 1024 768 512 256 0 100.00 106.67 113.33 120.00 126.67 133.33 140.00 146.67 153.33 160.00 166.67 mV s 300 160 80 200 240 2000 0.4 Hz Hz V V mV
DIGITAL SOFT-START AND BINNING
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5
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming MAX16816
ELECTRICAL CHARACTERISTICS (continued)
(VCC = VUVEN = 14V, CREG1 = 1F, CREG2 = 1F, CCLMP = 0.1F, RT = 25k, TA = TJ = -40C to +125C, unless otherwise noted. Typical specifications are at TA = +25C.)
PARAMETER SLOPE COMPENSATION Slope Compensation register is `0000', clock generated by RT Slope Compensation register is `0001', clock generated by RT Slope Compensation register is `0010', clock generated by RT Slope Compensation register is `0011', clock generated by RT Slope Compensation register is `0100', clock generated by RT Slope Compensation register is `0101', clock generated by RT Slope Compensation register is `0110', clock generated by RT Slope Compensation Peak-toPeak Voltage Per Cycle Slope Compensation register is `0111', clock generated by RT Slope Compensation register is `1000', clock generated by RT Slope Compensation register is `1001', clock generated by RT Slope Compensation register is `1010', clock generated by RT Slope Compensation register is `1011', clock generated by RT Slope Compensation register is `1100', clock generated by RT Slope Compensation register is `1101', clock generated by RT Slope Compensation register is `1110', clock generated by RT Slope Compensation register is `1111', clock generated by RT 0 20 40 60 80 100 120 140 mV/ cycle 160 180 200 220 240 260 280 300 SYMBOL CONDITIONS MIN TYP MAX UNITS
6
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
ELECTRICAL CHARACTERISTICS (continued)
(VCC = VUVEN = 14V, CREG1 = 1F, CREG2 = 1F, CCLMP = 0.1F, RT = 25k, TA = TJ = -40C to +125C, unless otherwise noted. Typical specifications are at TA = +25C.)
PARAMETER SYMBOL CONDITIONS Slope Compensation register is `0000', external clock applied to RTSYNC Slope Compensation register is `0001', external clock applied to RTSYNC Slope Compensation register is `0010', external clock applied to RTSYNC Slope Compensation register is `0011', external clock applied to RTSYNC Slope Compensation register is `0100', external clock applied to RTSYNC Slope Compensation register is `0101', external clock applied to RTSYNC Slope Compensation register is `0110', external clock applied to RTSYNC Slope Compensation register is `0111', external clock applied to RTSYNC Slope Compensation Slope Compensation register is `1000', external clock applied to RTSYNC Slope Compensation register is `1001', external clock applied to RTSYNC Slope Compensation register is `1010', external clock applied to RTSYNC Slope Compensation register is `1011', external clock applied to RTSYNC Slope Compensation register is `1100', external clock applied to RTSYNC Slope Compensation register is `1101', external clock applied to RTSYNC Slope Compensation register is `1110', external clock applied to RTSYNC Slope Compensation register is `1111', external clock applied to RTSYNC 16 18 20 22 24 26 28 30 MIN TYP 0 2 4 6 8 10 12 14 mV/s MAX UNITS
MAX16816
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7
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming MAX16816
ELECTRICAL CHARACTERISTICS (continued)
(VCC = VUVEN = 14V, CREG1 = 1F, CREG2 = 1F, CCLMP = 0.1F, RT = 25k, TA = TJ = -40C to +125C, unless otherwise noted. Typical specifications are at TA = +25C.)
PARAMETER FAULT I/O FAULT Leakage Current FAULT Input Low Current FAULT Pulldown Current FAULT Pulldown Input Logic-Low FAULT Output Logic-High FAULT Output Logic-Low Programming Slot at Power-Up THERMAL SHUTDOWN Thermal Shutdown Temperature Thermal Shutdown Hysteresis EEPROM Data Retention EEPROM Write Time Endurance tDR tWRA TA = +125C (Note 5) (Note 5) TA = +85C, read and write (Note 5) 50k 10 14 years ms cycles TJ_SHDN TJ_SHDN +165 20
o
SYMBOL
CONDITIONS 5.5V < VFAULT < 76V VFAULT = 0V VFAULT = 2V
MIN -1
TYP
MAX +1
UNITS A A mA V V
500 0.7 1.2 1.8 0.4
VIL Sourcing 10A Sinking 10A VUVEN > 1.244V and VCC > 5.9V (Note 4) 6.4 8.0 2.8
0.4
V ms
C C
o
ELECTRICAL CHARACTERISTICS - 1-Wire(R) System
(CREG1 = 1F, CREG2 = 1F, TA = TJ = -40C to +125C, unless otherwise noted. Typical specifications are at TA = +25C.)
PARAMETER I/O GENERAL DATA 1-Wire Time Slot Duration Recovery Time Reset Low Time Presence Detect Sample Time I/O, 1-Wire WRITE Write-0 Low Time Write-1 Low Time I/O, 1-Wire READ Read Low Time Read Sample Time tRL tMSR 5 12 10 15 s s tW0L tW1L 60 5 15 s s tSLOT tREC tRSTL tMSP (Note 6) 65 5 480 65 640 75 s s s s SYMBOL CONDITIONS MIN TYP MAX UNITS
I/O, 1-Wire RESET, PRESENCE DETECT CYCLE
1-Wire is a registered trademark of Dallas Semiconductor Corp., a wholly owned subsidiary of Maxim Integrated Products, Inc.
8
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
ELECTRICAL CHARACTERISTICS
Note 1: Dropout voltage is defined as the input to output differential voltage at which the output voltage drops 100mV below its nominal value measured at output. Note 2: VCLMP_TH determines the voltage necessary to operate the current-sense amplifier. The DIM driver requires 2.5V for (VCLMP - VLO) to drive a FET. VHI is typically one diode drop above VCLMP. A large capacitor connected to VCLMP slows the response of the LED current-sense circuitry, resulting in current overshoot. To ensure proper operation, connect a 0.1F capacitor from CLMP to LO. Note 3: Minimum pulse width required to guarantee proper dimming operation. Note 4: FAULT multiplexes a programming interface and fault indication functionality. At power-up initialization, an internal timer enables FAULT and two programming passcodes must be entered within the programming slot to enter programming mode. If the programming passcodes are not received correctly within the programming slot, FAULT goes back towards fault indication. Cycling power to the device is required to re-attempt entry into programming mode. Note 5: Not production tested. Guaranteed by design. Note 6: Recovery time is the time required for FAULT to be pulled high by the internal 10k resistor.
MAX16816
Typical Operating Characteristics
(VCC = VUVEN = 14V, CREG1 = 1F, CREG2 = 10F, CCLMP = 0.1F, RCS = 0.1, Binning adjustment register is `0000', TA = +25C, unless otherwise noted.)
SHUTDOWN CURRENT vs. TEMPERATURE
MAX16816 toc01
OPERATING CURRENT vs. TEMPERATURE
MAX16816 toc02
OUTPUT CURRENT vs. TEMPERATURE
550 500 LED CURRENT (mA) 450 400 350 RCS = 0.3 300 250 200 -60 -40 -20 0 20 40 60 80 100 120 140 RCS = 0.2
MAX16816 toc03
26 25 24 ISHDN_VCC (A)
4.0 3.8 3.6 ICC (mA) 3.4 3.2 3.0 2.8 2.6 DGT AND DRV NOT SWITCHING -60 -40 -20 0
600
23 22 21 20 19 18 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (C)
20 40 60 80 100 120 140
TEMPERATURE (C)
TEMPERATURE (C)
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9
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming MAX16816
Typical Operating Characteristics (continued)
(VCC = VUVEN = 14V, CREG1 = 1F, CREG2 = 10F, CCLMP = 0.1F, RCS = 0.1, Binning adjustment register is `0000', TA = +25C, unless otherwise noted.)
OUTPUT CURRENT vs. SUPPLY VOLTAGE
MAX16816 toc04
OUTPUT CURRENT vs. BINNING CODES
MAX16816 toc05
OUTPUT CURRENT vs. BINNING CODES
800 OUTPUT CURRENT (mA) 700 600 500 400 300 200 100 0 RCS = 0.2 0 1 2 3 4 5 6 7 8 9
MAX16816 toc06
350 300 LED CURRENT (mA) 250 200 150 100 50 0 0 8
1.8 1.6 1.4 LED CURRENT (A) 1.2 1.0 0.8 0.6 0.4 0.2 0
900
16 24 32 40 48 56 64 72 80 VCC (V)
0
1
2
3
4
5
6
7
8
9
BIN (DIGITAL CODE)
BIN (DIGITAL CODE)
REG2 OUTPUT VOLTAGE vs. TEMPERATURE
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
MAX16816 toc07
REG2 OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
MAX16816 toc08
REG2 OUTPUT VOLTAGE vs. REG2 CONTROL REGISTER
16 15 14 13 12 11 10 9 8 7 6 5 4 IREG2 = 20mA 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 DRPS (DIGITAL CODE)
MAX16816 toc09
18 16 REG2 OUTPUT VOLTAGE (V) 14 12 10 8 6 4 2 0 0
REG2 CONTROL REGISTER = '1111', VCC = 20V
REG2 CONTROL REGISTER = '1111', VCC = 20V
REG2 OUTPUT VOLTAGE (V)
REG2 CONTROL REGISTER = '0000'
REG2 CONTROL REGISTER = '0000' IREG2 = 20mA 8 16 24 32 40 48 56 64 72 80 VCC (V)
IREG2 = 20mA -60 -40 -20 0 20 40 60 80 100 120 140
TEMPERATURE (C)
REG2 OUTPUT VOLTAGE (V)
REG1 OUTPUT VOLTAGE vs. TEMPERATURE
MAX16816 toc10
REG1 OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
MAX16816 toc11
CLMP OUTPUT VOLTAGE vs. TEMPERATURE
8.2 CLMP OUTPUT VOLTAGE (V) 8.1 8.0 7.9 7.8 7.7 7.6 7.5 80 -60 -40 -20 0 VHI - VLO = 9V CLMP VOLTAGE = VCLMP - VLO 20 40 60 80 100 120 140
MAX16816 toc12
5.4 5.3 REG1 OUTPUT VOLTAGE (V) 5.2 5.1 5.0 4.9 4.8 4.7 IREG1 = 2mA 4.6 -60 -40 -20 0
6 5 REG1 OUTPUT VOLTAGE (V) 4 3 2 1 IREG1 = 2mA 0 0 10 20 30 40 VCC (V) 50 60 70
8.3
20 40 60 80 100 120 140
TEMPERATURE (C)
TEMPERATURE (C)
10
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
Typical Operating Characteristics (continued)
(VCC = VUVEN = 14V, CREG1 = 1F, CREG2 = 10F, CCLMP = 0.1F, RCS = 0.1, Binning adjustment register is `0000', TA = +25C, unless otherwise noted.)
REF VOLTAGE vs. TEMPERATURE
3.10 3.08 REF VOLTAGE (V) 3.06 3.04 3.02 3.00 2.98 IREF = 100A 2.96 -60 -35 -10 15 40 65 90 115 140 TEMPERATURE (C) 3.000 -225 -175 -125 -75 -25 25 IREF (A) 75 125 175 225 REF VOLTAGE (V)
MAX16816 toc13
MAX16816
REF VOLTAGE vs. SINK CURRENT
MAX16816 toc14
PWM OSCILLATION FREQUENCY vs. TEMPERATURE
135 134 133 132 131 130 129 128 127 126 125 124 123 122 121 120 -60 -35 -10 15 40 65 TEMPERATURE (C)
MAX16816 toc15
3.12
3.025
3.020
3.015
3.010
3.005
PWM FREQUENCY (kHz)
RT = 100k 90 115 140
RT RESISTANCE vs. PWM FREQUENCY
MAX16816 toc16
200Hz DIMMING OPERATION
MAX16816 toc17
LED CURRENT DUTY CYCLE vs. DIM VOLTAGE
90 LED CURRENT DUTY CYCLE (%) 10% DIMMING 1A/div 50% DIMMING 1A/div 90% DIMMING 1A/div 80 70 60 50 40 30 20 10 0 0 1 2 3
MAX16816 toc18
550 500 PWM FREQUENCY (kHz) 450 400 350 300 250 200 150 100 0.005 0.015 0.025 0.035
100
0A
0A
0A
0.045
2ms/div
1/RT RESISTANCE (k-1)
DIM VOLTAGE (V)
DRIVER DRV RISE TIME vs. DRI VOLTAGE
MAX16816 toc19
DRIVER DRI FALL TIME vs. DRI VOLTAGE
40 35 DRV FALL TIME (ns) 30 25 20 15 10
MAX16816 toc20
70 60 DRV RISE TIME (ns) 50 40 30 20 10 0 5 7 9 11 13 5nF CAPACITOR CONNECTED FROM DRV TO AGND
45
5 0 15 5 7
5nF CAPACITOR CONNECTED FROM DRV TO AGND 9 11 13 15
DRI VOLTAGE (V)
DRI VOLTAGE (V)
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11
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming MAX16816
Pin Description
PIN 1, 24 NAME N.C. No Connection. Not internally connected. Undervoltage Lockout (UVLO) Threshold/Enable Input. UVEN is a dual-function adjustable UVLO threshold input with an enable feature. Connect UVEN to VCC through a resistive voltage-divider to program the UVLO threshold. Connect UVEN directly to VCC to use the 5.9V (max) default UVLO threshold. Apply a voltage greater than 1.244V to UVEN to enable the device. 5V Regulator Output. REG1 is an internal low-dropout voltage regulator that generates a 5V (VCC > 6V) output voltage and supplies power to internal circuitry. Bypass REG1 to AGND through a 1F ceramic capacitor. Analog Ground. Use proper single-point ground design and decoupling to avoid ground impedance loop errors. Accurate 3V Buffered Reference Output. Connect REF to DIM through a resistive voltage-divider to apply a DC voltage for analog-controlled dimming functionality. Leave REF unconnected if unused. Dimming Control Input. Connect DIM to an external PWM signal for PWM dimming. For analog-controlled dimming, connect DIM to REF through a resistive voltage-divider. The dimming frequency is 200Hz under these conditions. Connect DIM to AGND to turn off the LEDs. Sync Input/Output. The internal PWM clock is selectable through the RTOF EEPROM bit. Connect an external resistor to RTSYNC and set the RTOF register to `0' to select a clock frequency between 125kHz and 500kHz. Set RTOF register to `0' and connect RTSYNC to an external clock to synchronize the device with external clock. Set RTOF register to `1' to use the fixed 125kHz oscillator. Under these conditions, RTSYNC is powered off and may be left in any state. See the Oscillator, Clock, and Synchronization section. Clock Output. CLKOUT buffers the oscillator/clock. Connect CLKOUT to the SYNC input of another device to operate the MAX16816 in a multichannel configuration. CLKOUT is a logic output. Internally Connected. Must be connected to AGND. Error-Amplifier Output. Connect the compensation network from COMP to FB for stable closed-loop control. Use low-leakage ceramic capacitors in the feedback network. Current-Sense Voltage Output. CS outputs a voltage proportional to the current sensed through the currentsense amplifier. Connect CS through a passive network to FB as dictated by the chosen compensation scheme. Error-Amplifier Inverting Input Overvoltage Protection Input. Connect OV to HI through a resistive voltage-divider to set the overvoltage limit for the load. When the voltage at OV exceeds the 1.235V (typ) threshold, an overvoltage fault is generated and the switching MOSFET turns off. The MOSFET is turned on again when the voltage at OV drops below 1.17V (typ). Switching Ground. SGND is the ground for non-analog and high-current gate-driver circuitry. Gate-Driver Output. Connect DRV through a series resistor to the gate of an external n-channel MOSFET to reduce EMI. DRV can sink 1A or source 0.5A. Gate-Driver Supply Input. Connect DRI to REG2 to power the primary switching MOSFET driver. Positive Peak Current-Sense Input. Connect SNS+ to the positive side of the switch current-sense resistor, RSENSE. FUNCTION
2
UVEN
3
REG1
4 5
AGND REF
6
DIM
7
RTSYNC
8 9, 10, 11 12
CLKOUT I.C. COMP
13 14
CS FB
15
OV
16, 17 18 19 20
SGND DRV DRI SNS+
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
Pin Description (continued)
PIN 21 22 23 NAME SNSQGND DGT FUNCTION Negative Peak Current-Sense Input. Connect SNS- to the negative side of the switch current-sense resistor, RSENSE. Analog Ground. Ensure a low-impedance connection between QGND and AGND. Dimming Gate-Driver Output. Connect DGT to the gate of an external n-channel MOSFET for dimming. DGT is powered by the internal regulator, CLAMP, and is referenced to LO. Low-Voltage Input. LO is the return point for the LED current. When using the MAX16816 in a buck-boost configuration, connect LO to VCC. When using the device in a boost configuration only, connect LO to AGND. Connect LO to the junction of the inductor and LED current-sense resistor, RCS, when using a buck configuration. Noninverting Current-Sense Amplifier Input. Connect CS+ to the positive side of an external sense resistor, RCS, connected in series with the load (LEDs). Inverting Current-Sense Amplifier Input. Connect CS- to the negative side of an external sense resistor, RCS, connected in series with the load (LEDs). Internal CLAMP Regulator Bypass. CLAMP supplies an 8V (typ) output when VHI 9V. If VHI is lower than 9V, VCLMP is one diode drop below VHI. The CLAMP regulator powers the current-sense amplifier and provides the high reference for the dimming driver. VCLMP must be at least 2.5V higher than VLO to enable the current-sense amplifier and dimming MOSFET driver. Bypass CLMP to LO with a 0.1F ceramic capacitor. High-Voltage Input. HI is referred to LO. HI supplies power to the current-sense amplifier and dimming MOSFET gate driver through the CLMP regulator. Internal Regulator Output. REG2 is an internal voltage regulator that generates EEPROM-programmable (5V to 15V) output and supplies power to internal circuitry. Connect REG2 to DRI to power the switching MOSFET driver during normal operation. Bypass REG2 to AGND with a 10F ceramic capacitor. Supply Voltage Input FAULT Input/Output. FAULT is a bidirectional high-voltage logic input/output. FAULT multiplexes a 1-Wire programming interface with a fault indicator. FAULT is internally pulled up to 5V through a 10k resistor and a 1.8mA (max) current pulldown to ground. Exposed Pad. Connect EP to AGND. EP also functions as a heatsink to maximize thermal dissipation. Do not use as the main ground connection.
MAX16816
25
LO
26 27
CS+ CS-
28
CLMP
29
HI
30 31 32
REG2 VCC FAULT
EP
EP
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming MAX16816
Functional Diagram
VCC CLMP HI CS- CS+ LO
UVLO AND EN UVEN D-I THERMAL SHUTDOWN QGND REG1 VBUF 3.0V + SLOPE SLOPE COMP D-I REF VLO + CMP 1.3 x V SS OSC OC UGB DDR REG2 DRIVER VCLMP
CSA
5V REG1 15V REG2 CLAMP VCLMP VLO REG2
RLS
+
DGT
CS 1-Wire INTERFACE FAULT
RTSYNC OSC CLKOUT POR VOV OVP OV + + ILIM - 200mV + HIC 300mV EN OV
DRI CONTROL BLOCK DRIVER DRV SGND SNS+ SNS-
DIM +
+ COMP
AGND
200mV
-
D-I BLANKING BLANKING TIME
200Hz
MAX16816
PWM SLOPE 0.926V OS TRIM REGISTERS BLANKING SLOPE COMP BINNING REG2 DRIVER SOFT-START RTOSCSEL SS X1 + VSS EAMP D-I D-I D-I BINNING SOFT-START COMP FB
- 800mV +
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D-I
INDICATES A USER-PROGRAMMABLE EEPROM FEATURE
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
Detailed Description
The MAX16816 is a current-mode PWM LED driver for use in driving HB LEDs. An output current accuracy of 5% is achievable using two current regulation loops: one current regulation loop controls the external switching MOSFET peak current through a sense resistor, RSENSE, from SNS+ to SNS- while the other current regulation loop controls the average LED string current through the sense resistor, R CS , in series with the LEDs. The wide operating supply range of 5.9V/5.4V (ON/OFF) to 76V makes the MAX16816 ideal in automotive applications. The MAX16816 provides LED binning through one programmable on-chip nonvolatile EEPROM. The LED current can be scaled up to a factor of 1.6. This feature is used to offset factory LED luminance variations and allows the system to achieve overall luminance accuracy. A programmable undervoltage lockout (UVEN) ensures predictable operation during brownout conditions. The UVEN input circuitry monitors the supply voltage, VCC, and turns the driver off when V CC drops below the UVLO threshold. Connect UVEN to VCC to use the 5.7V (typ) default UVLO threshold. The MAX16816 includes a cycle-by-cycle current limit that turns off the gate drive to the external switching MOSFET (QS) during an overcurrent condition and a programmable oscillator that simplifies and optimizes the design of external magnetics. The MAX16816 is capable of synchronizing to an external clock or operating in a stand-alone mode. A single resistor, RT, can be used to adjust the switching frequency from 125kHz to 500kHz for stand-alone operation. To synchronize the device with an external clock, apply a clock signal directly to the RTSYNC input. A buffered clock output, CLKOUT, is available to configure the MAX16816 for multichannel applications. The external RT oscillator can be disabled by setting EEPROM register RTOF to `1'. The MAX16816 provides wide contrast pulsed dimming (up to 1000:1) utilizing a separate dimming input. Apply either a DC level voltage or low-frequency PWM signal to the dimming input. DC level input results in a 200Hz fixed dimming frequency. The MAX16816 provides configurable on-chip nonvolatile EEPROM features including a programmable soft-start, load current, external MOSFET gate-driver supply voltage, blanking time, and slope compensation. Protection features include peak current limiting, HICCUP mode current limiting, output overvoltage protection, short-circuit protection, and thermal shutdown. The HICCUP current-limit circuitry reduces the power delivered to the load during severe fault conditions. A nonlatching overvoltage protection limits the voltage on the external switching MOSFET (QS) under open-circuit conditions in the LED string. During continuous operation at high input voltages, the power dissipation of the MAX16816 could exceed the maximum rating and the internal thermal shutdown circuitry safely turns off the MAX16816 when the device junction temperature exceeds +165C. When the junction temperature drops below the hysteresis temperature, the MAX16816 automatically reinitiates startup.
MAX16816
Undervoltage Lockout/Enable (UVEN)
The MAX16816 features a dual-purpose adjustable undervoltage lockout input and enable function (UVEN). Connect UVEN to VCC through a resistive voltage-divider to set the undervoltage lockout (UVLO) threshold. The device is enabled when the voltage at UVEN exceeds the 1.244V (typ) threshold. Drive UVEN to ground to disable the output.
Setting the UVLO Threshold Connect UVEN directly to VCC to select the default 5.7V (typ) UVLO threshold. Connect UVEN to VCC through a resistive voltage-divider to select a UVLO threshold (Figure 1). Select the desired UVLO threshold voltage, VUVLO, and calculate resistor values using the following equation:
VUVEN RUV1 = RUV2 x VUVLO - VUVEN where RUV1 + RUV2 270k. VUVEN is the 1.244V (typ) UVEN threshold voltage.
VIN RUV2 UVEN VCC
MAX16816
CUVEN RUV1 QGND
Figure 1. Setting the UVLO Threshold
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
The capacitor CUVEN is required to prevent chattering at the UVLO threshold due to line impedance drops during power-up and dimming. If the undervoltage setting is very close to the required minimum operating voltage, there can be large jumps in the voltage at VCC during dimming, which may cause the MAX16816 to turn on and off when the dimming signal transitions from low to high. The capacitor CUVEN should be large enough to limit the ripple on UVEN to less than the 100mV (min) UVEN hysteresis so that the device does not turn off under these circumstances.
MAX16816
Reference Voltage Output (REF)
The MAX16816 includes a 5% accurate, 3V (typ) buffered reference output, REF. REF is a push-pull output capable of sourcing/sinking up to 200A of current and can drive a maximum load capacitance of 100pF. Connect REF to DIM through a resistive voltage-divider to supply an analog signal for dimming. See the Dimming Input (DIM) section for more information.
Dimming MOSFET Driver (DDR)
The MAX16816 requires an external n-channel MOSFET for PWM dimming. Connect the MOSFET to the output of the DDR dimming driver, DGT, for normal operation. VDGT swings between VLO and VCLMP. The DDR dimming driver is capable of sinking or sourcing up to 20mA of current. The average current required to drive the dimming MOSFET (I DRIVE_DIM) depends on the MOSFET's total gate charge (QG_DIM) and the dimming frequency of the converter, fDIM. Use the following equation to calculate the supply current for the n-channel dimming FET driver. IDRIVE_DIM = QG_DIM x fDIM
Soft-Start
The MAX16816 features a digitally programmable softstart delay that allows the load current to ramp up in a controlled manner, minimizing output overshoot. Softstart begins once the device is enabled and V CC exceeds the UVLO threshold. Soft-start circuitry slowly increases the internal soft-start voltage, VSS, resulting in a controlled rise of the load current. Signals applied to DIM are ignored until the soft-start duration is complete and a successive delay of 200s has elapsed. Use the Digital Soft-Start Duration register in the EEPROM to select a soft-start duration from 0 (no delay) to 4.096ms. See the EEPROM and Programming section for more information on using the Digital Soft-Start Duration register.
n-Channel MOSFET Switch Driver (DRV)
The MAX16816 drives an external n-channel MOSFET for switching. Use an external supply or connect REG2 to DRI to power the MOSFET driver. The driver output, VDRV, swings between ground and VDRI. Ensure that VDRI remains below the absolute maximum VGS rating of the external MOSFET. DRV is capable of sinking 2A or sourcing 1.4A of peak current, allowing the MAX16816 to switch MOSFETs in high-power applications. The average current sourced to drive the external MOSFET depends on the total gate charge (QG) and operating frequency of the converter, fSW. The power dissipation in the MAX16816 is a function of the average output drive current (IDRIVE). Use the following equations to calculate the power dissipation in the gate-driver section of the MAX16816 due to IDRIVE: IDRIVE = QG x fSW PD = IDRIVE x VDRI where VDRI is the supply voltage to the gate driver.
Regulators (REG1, REG2, CLAMP)
The MAX16816 includes a fixed 5V voltage regulator, REG1; an EEPROM-adjustable regulator, REG2; and an internal 8V regulator, CLAMP. REG1 and REG2 power up when VCC exceeds the UVLO threshold. REG1 supplies power to internal circuitry and remains on during PWM dimming. REG1 is capable of driving external loads up to 2mA. Use the REG2 Control Register in the EEPROM to select an output voltage from 5V to 15V for REG2. Connect REG2 to DRI to generate the supply voltage for the primary switching MOSFET driver, DRV. REG2 is capable of delivering up to 20mA of current. See the EEPROM and Programming section for more information on configuring the REG2 output voltage. CLAMP is powered by HI and supplies power to the current-sense amplifier (CSA). CSA is enabled when V CLMP goes 2.5V above V LO and is disabled when (VCLMP - VLO) falls below 2.28V. The CLAMP regulator also provides power to the dimming MOSFET control circuitry. CLMP is the output of the CLAMP regulator. Do not use CLMP to power external circuitry. Bypass CLMP to LO with a 0.1F ceramic capacitor. A larger capacitor will result in overshoot of the load current.
Dimming Input (DIM)
The dimming input, DIM, functions with either analog or PWM control signals. Once the internal pulse detector detects three successive edges of a PWM signal with a frequency between 80Hz and 2kHz, the MAX16816 synchronizes to the external signal and pulse-width modulates the LED current at the external DIM input frequency with the same duty cycle as the DIM input. If
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
an analog control signal is applied to DIM, the MAX16816 compares the DC input to an internally generated 200Hz ramp to pulse-width modulate the LED current (fDIM = 200Hz). The output current duty cycle is linearly adjustable from 0 to 100% (0.2V < VDIM < 2.8V). Use the following formula to calculate voltage, VDIM, necessary for a given output current duty cycle, D: VDIM = (D x 2.6) + 0.2V where VDIM is the voltage applied to DIM in volts. Connect DIM to REF through a resistive voltage-divider to apply a DC DIM control signal (Figure 2). Use the required dimming input voltage, V DIM , calculated above and select appropriate resistor values using the following equation: R4 = R3 x VDIM / (VREF - VDIM) where V REF is the 3V reference output voltage and 15k R3 + R4 150k. A minimum 20s pulse width is necessary for proper operation during dimming. To synchronize the MAX16816 with an external clock signal ranging from 125kHz to 500kHz, set the RTOF bit to `0' and connect the clock signal to the RTSYNC input. The MAX16816 synchronizes to the clock signal after the detection of 5 successive clock edges at RTSYNC. A buffered clock output, CLKOUT, can drive the RTSYNC input of an external PWM controller for multichannel applications. CLKOUT can drive capacitive loads up to 500pF. If the PWM switching frequency is set to 125kHz, the RTSYNC oscillator can be temporarily disabled by setting the EEPROM RTOF bit to `1'. In this case, the internal 125kHz frequency-fixed oscillator drives the PWM. See the EEPROM and Programming section for more information on setting the Oscillator Enable/Disable bit in the EEPROM.
MAX16816
Multichannel Configuration
The MAX16816 is capable of multichannel operation and is configurable as a master or slave in a MasterSlave configuration, or in a Peer-to-Peer configuration. Connect CLKOUT to the SYNC input of an external device to use the MAX16816 as a master clock signal. Connect an external clock signal to RTSYNC to configure the MAX16816 as a slave. To setup two MAX16816 devices in a daisy-chain configuration, drive the RTSYNC input of one MAX16816 with the CLKOUT buffer of another (Figure 3).
Oscillator, Clock, and Synchronization
The MAX16816 is capable of stand-alone operation, of synchronizing to an external clock, and of driving external devices in SYNC mode. For stand-alone operation, set the EEPROM Oscillator Enable/Disable (RTOF) bit to `1' to use the fixed internal 125kHz oscillator or set RTOF to `0' and program the switching frequency by connecting a single external resistor, R T , between RTSYNC and ground. Select a switching frequency, fSW, between 125kHz and 500kHz and calculate RT using the following formula: RT = 500kHz x 25k fSW
ILIM and HICCUP Comparator
RSENSE sets the peak current through the inductor for switching. The differential voltage across RSENSE is compared to the 200mV voltage-trip limit of the currentlimit comparator, ILIM. Set the current limit 20% higher than the peak switch current at the rated output power and minimum voltage. Use the following equation to calculate RSENSE: RSENSE = VSENSE / (1.2 x IPEAK)
where the switching frequency is in kHz and RT is in k.
REF R3 DIM AGND R4 RT
MASTER/PEER
SLAVE/PEER
MAX16816 MAX16816
RTSYNC CLKOUT
MAX16816
RTSYNC CLKOUT
Figure 2. Creating DIM Input Signal from REF
Figure 3. Master-Slave/Peer-Peer Clock Configuration
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
where VSENSE is the 200mV maximum differential voltage between SNS+ and SNS- and IPEAK is the peak inductor current at full load and minimum input voltage. When the voltage drop across RSENSE exceeds the ILIM threshold, the MOSFET driver (DRV) terminates the on-cycle and turns the switch off, reducing the current through the inductor. The FET is turned back on at the beginning of the next switching cycle. When the voltage across RSENSE exceeds the 300mV (typ) HICCUP threshold, the HIC comparator terminates the on-cycle of the device, turning the switching MOSFET off. Following a startup delay of 8ms (typ), the MAX16816 reinitiates soft-start. The device will continue to operate in HICCUP mode until the overcurrent condition is removed. A programmable built-in leading-edge blanking circuit of the current-sense signal prevents these comparators from prematurely terminating the on-cycle of the external switching MOSFET (Q S). Select a blanking time from 75ns to 150ns by configuring the Blanking Time register in the EEPROM. In some cases, the maximum blanking time may not be adequate and an additional RC filter may be required to prevent spurious turn-off.
MAX16816
See the EEPROM and Programming section for more information on the ESLP register.
Internal Voltage-Error Amplifier (EAMP)
The MAX16816 includes a built-in voltage amplifier, with three-state output, which can be used to close the feedback loop. The buffered output current-sense signal appears at CS, which is connected to the inverting input, FB, of the error amplifier through resistor R1. The noninverting input is connected to an internally trimmed current reference. The output of the error amplifier is controlled by the signal applied to DIM. When DIM is high, the output of the amplifier is connected to COMP. The amplifier output is open when DIM is low. This enables the integrating capacitor to hold the charge when the DIM signal has turned off the gate drive. When DIM is high again, the voltage on the compensation capacitors, C1 and C2, forces the converter into steady state almost instantaneously.
PWM Dimming
PWM dimming is achieved by driving DIM with either a PWM signal or a DC signal. The PWM signal is connected internally to the error amplifier, the dimming MOSFET gate driver, and the switching MOSFET gate driver. When the DIM signal is high, the dimming MOSFET and the switching MOSFET drivers are enabled and the output of the voltage-error amplifier is connected to the external compensation network. Also, the buffered current-sense signal is connected to CS. Preventing discharge of the compensation capacitor when the DIM signal is low allows the control loop to return the LED current to its original value almost instantaneously. When the DIM signal goes low, the output of the error amplifier is disconnected from the compensation network and the compensation capacitors, C1 and C2, voltage is preserved. Choose low-leakage capacitors for C1 and C2. The drivers for the external dimming and switching MOSFETs are disabled, and the converter stops switching. The inductor energy is now transferred to the output capacitors. When the DIM signal goes high and the gate drivers are enabled, the additional voltage on the output capacitor may cause a current spike on the LED string. A larger output capacitor will result in a smaller current spike. If the overcurrent spike exceeds 30% of the programmed LED current, the dimming is turned off and the MAX16816 reinitiates soft-start.
Load Current Sense
The load sense resistor, R CS , monitors the current through the LEDs. The internal floating current-sense amplifier, CSA, measures the differential voltage across RCS, and generates a voltage proportional to the load current through R CS at CS. This voltage on CS is referred to AGND. The closed-loop regulates the load current to a value, ILED, given by the following equation: ILED = VSS / RCS where VSS is the binning adjustment voltage. Set the value of VSS in the Binning Adjustment register in the EEPROM between 100mV and 166mV. See the EEPROM and Programming section for more information on adjusting the binning voltage.
Slope Compensation
The amount of slope compensation required is largely dependent on the down-slope of the inductor current when the switching MOSFET, QS, is off. The inductor down-slope depends on the input-to-output voltage differential of the converter, the inductor value, and the switching frequency. For stability, the compensation slope should be equal to or greater than half of the inductor current down-slope multiplied by the currentsense resistance (RSENSE).
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
FAULT 1-Wire Interface
The MAX16816 features a FAULT output multiplexed with a 1-Wire programming interface. Once the voltage at UVEN exceeds the UVLO threshold, the device is enabled and FAULT will pulse low once, indicating the beginning of the programming window. Two programming mode entry codes must be entered within 8ms after the pulse to enter programming mode (see Table 1). The MAX16816 will register the second entry code only after the first code has been received. Once the MAX16816 successfully enters programming mode, the data and clock for the 1-Wire interface are supplied through FAULT. Once the programming window has passed, the EEPROM is no longer accessible without cycling power to the device. Under these conditions, FAULT will go low only when a fault (overvoltage, overcurrent, or HICCUP mode) occurs or when the supply voltage drops below the UVLO threshold.
MAX16816
EEPROM and Programming
Nonvolatile EEPROM is available to configure the MAX16816 through a 1-Wire serial interface. Registers are located in a linear address space as shown in Table 2. All other EEPROM locations are reserved. Configure the six control registers to adjust parameters including the REG2 voltage, soft-start durations, blanking time, LED load current (binning), slope compensation, and to enable/disable the RTOF oscillator. See the 1-Wire Interface section for more information about 1-Wire programming.
Table 1. Programming Mode Entry Codes
PROGRAMMING MODE ENTRY CODE PASS_CODE_1 PASS_CODE_2 D7 0 0 D6 0 0 D5 1 0 D4 0 0 D3 1 1 D2 0 0 D1 0 0 D0 1 1 HEX CODE 29h 09h
Table 2. EEPROM Memory Map
REGISTER Binning Adjustment (BIN) REG2 Control (DRPS) Blanking Time Adjustment (BLNK) Digital Soft-Start Duration (SS) Internal Oscillator Enable/Disable (RTOF) Slope Compensation (ESLP) EEPROM ADDRESS RANGE 24h-27h 28h-2Bh 32h-33h 34h-36h NO. OF BITS 4 4 2 2 TYPE R/W R/W R/W R/W DESCRIPTION Adjusts the LED current. Sets the output voltage for REG2. Connect REG2 to DRI to supply the high-side voltage for the gate driver, DRV. Adjusts the blanking time for debouncing. Adjusts the soft-start duration to allow the load current to ramp up in a controlled manner, minimizing output overshoot. Enables/disables the internal oscillator for stand-alone operation or to synchronize with an external clock. Adjusts the slope compensation for stability.
37h 38h-3Bh
1 4
R/W R/W
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
Binning Adjustment Register (BIN) The MAX16816 uses a feedback loop to control the load current. The differential voltage across the currentsense resistor, R CS , is compared with an internal adjustable reference to regulate the LED current. The voltage across the sense resistor is measured differentially to achieve high immunity to common-mode noise. The MAX16816 includes a factory-set regulation voltage of 133mV 3% across RCS. Adjust the differential regulation voltage by programming the binning adjustment register (see Table 3). The reference voltage level may not necessarily be equal to the regulation voltage. There are offsets involved that are trimmed at the factory. Read the default register code and step up the code by one to increase the regulation voltage by 6.66mV. Step down the code by one to reduce the regulation voltage by 6.66mV. REG2 Control Register (DRPS) REG2 is EEPROM configurable to supply a voltage ranging from 5V to 15V and is capable of sourcing up to 20mA. Connect REG2 to the primary switching MOSFET gate-driver supply input, DRI, for normal operation.
MAX16816
Adjust REG2 by programming the REG2 Control Register. See Table 4.
Blanking Time Adjustment Register (BLNK) The MAX16816 features a programmable blanking time to mask out the current-sense signal for a short duration to avoid the ILIM and HICCUP comparators from prematurely terminating the on-cycle of the switching MOSFET. This blanking time allows for higher input current during startup without triggering a fault condition. The blanking time is adjustable in the range of 150ns to 75ns by configuring the EEPROM. See Table 5.
Table 4. REG2 Control Register
REG2 OUTPUT VOLTAGE (V) 5.000 5.667 6.333 7.000* 7.667 8.333 9.000 9.667 10.333 11.000 11.667 12.333 13.000 13.667 14.333 15.000 EEPROM ADDRESS 2Bh 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 2Ah 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 29h 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 28h 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
Table 3. Binning Adjustment Register
REFERENCE VOLTAGE LEVEL (mV) 100.00 106.67 113.33 120.00 126.67 133.33 140.00 146.67 153.33 160.00 166.67 173.33* 180.00* 186.67* 193.33* 200.00* EEPROM ADDRESS 27h 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 26h 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 25h 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 24h 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
*Factory default
Table 5. Blanking Time
BLANKING TIME (ns) 150* 125 100 75 *Factory default EEPROM ADDRESS 33h 0 0 1 1 32h 0 1 0 1
*Not recommended
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
Digital Soft-Start Duration Register (SS) The MAX16816 programmable soft-start feature allows the load current to ramp up in a controlled manner, eliminating output overshoot during startup. Soft-start begins once the device is enabled and VCC has exceeded the 5.5V (min) rising threshold voltage. Adjust the soft-start duration by configuring the EEPROM. Enter `111' to disable the soft-start feature. See Table 6. Oscillator Enable/Disable Register (RTOF) The MAX16816 features a programmable accurate RTSYNC oscillator and resistor synchronized to an external clock. Set the EEPROM bit RTOF to `1' to disable the external sync mode, and the RTSYNC oscillator, and to use the fixed internal frequency of 125kHz as the switching frequency. Set RTOF to `0' to synchronize with an external oscillator or to program the external oscillator frequency with an external resistor, RT. See Table 7. Slope Compensation Register (ESLP) The MAX16816 uses an internally generated ramp to stabilize the current loop when operating at duty cycles above 50%. Set the compensating slope by adjusting the peak ramp voltage through the on-chip EEPROM. See Tables 8 and 9.
Table 8. Slope Compensation with Clock Generated by RT Oscillator
SLOPE COMPENSATION (mV/clock cycle) 0 20 40 60 80 100 120* 140 160 180 200 220 240 260 280 300 *Factory default EEPROM ADDRESS 3Bh 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 3Ah 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 39h 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 38h 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
MAX16816
Table 6. Digital Soft-Start Duration
DURATION (s) 4096* 2048 1860 1024 768 512 256 No SS EEPROM ADDRESS 36h 0 0 0 0 1 1 1 1 35h 0 0 1 1 0 0 1 1 34h 0 1 0 1 0 1 0 1
Table 9. Slope Compensation with External Clock Applied to RTSYNC or RT Oscillator Off
SLOPE COMPENSATION (mV/s) 0 2 4 6 8 10 12* 14 16 18 20 22 24 26 28 30 EEPROM ADDRESS 3Bh 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 3Ah 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 39h 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 38h 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
*Factory default
Table 7. Oscillator Enable/Disable
RT OSCILLATOR RT Oscillator Off RT Oscillator On* EEPROM ADDRESS 37h 1 0
*Factory default
*Factory default
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming MAX16816
Fault Protection
The MAX16816 features built-in overvoltage protection, overcurrent protection, HICCUP mode current-limit protection, and thermal shutdown. Overvoltage protection is achieved by connecting OV to HI through a resistive voltage-divider. HICCUP mode limits the power dissipation in the external MOSFETs during severe fault conditions. Internal thermal shutdown protection safely turns off the converter when the IC junction temperature exceeds +165C.
Applications Information
Inductor Selection
The minimum required inductance is a function of operating frequency, input-to-output voltage differential, and the peak-to-peak inductor current (I L ). Higher I L allows for a lower inductor value while a lower I L requires a higher inductor value. A lower inductor value minimizes size and cost, improves large-signal transient response, but reduces efficiency due to higher peak currents and higher peak-to-peak output ripple voltage for the same output capacitor. On the other hand, higher inductance increases efficiency by reducing the ripple current, IL. However, resistive losses due to extra turns can exceed the benefit gained from lower ripple current levels, especially when the inductance is increased without also allowing for larger inductor dimensions. A good compromise is to choose IL equal to 30% of the full load current. The inductor saturating current is also important to avoid runaway current during the output overload and continuous short circuit. Select the ISAT to be higher than the maximum peak current limit. Buck configuration: In a buck configuration the average inductor current does not vary with the input. The worstcase peak current occurs at high input voltage. In this case the inductance, L, for continuous conduction mode is given by: L= VOUT x ( VINMAX - VOUT ) VINMAX x fSW x IL
Overvoltage Protection The overvoltage protection (OVP) comparator compares the voltage at OV with a 1.235V (typ) internal reference. When the voltage at OV exceeds the internal reference, the OVP comparator terminates PWM switching and no further energy is transferred to the load. The MAX16816 reinitiates soft-start once the overvoltage condition is removed. Connect OV to HI through a resistive voltage-divider to set the overvoltage threshold at the output. Setting the Overvoltage Threshold Connect OV to HI or to the high-side of the LEDs through a resistive voltage-divider to set the overvoltage threshold at the output (Figure 4). The overvoltage protection (OVP) comparator compares the voltage at OV with a 1.235V (typ) internal reference. Use the following equation to calculate resistor values:
VOV_LIM - VOV ROV1 = ROV2 x VOV where VOV is the 1.235V OV threshold. Choose ROV1 and ROV2 to be reasonably high value resistors to prevent discharge of filter capacitors. This will prevent unnecessary undervoltage and overvoltage conditions during dimming.
where VINMAX is the maximum input voltage, fSW is the switching frequency, and VOUT is the output voltage.
Load-Dump Protection The MAX16816 features load-dump protection up to 76V. LED drivers using the MAX16816 can sustain single fault load dump events. Repeated load dump events within very short time intervals can cause damage to the dimming MOSFET due to excess power dissipation. Thermal Shutdown The MAX16816 contains an internal temperature sensor that turns off all outputs when the die temperature exceeds +165C. Outputs are enabled again when the die temperature drops below +145C.
VLED+
MAX16816
ROV1 OV AGND ROV2
Figure 4. Setting the Overvoltage Threshold
22 ______________________________________________________________________________________
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
Boost configuration: In the boost converter, the average inductor current varies with line and the maximum average current occurs at low line. For the boost converter, the average inductor current is equal to the input current. In this case the inductance, L, is calculated as: L= VINMIN x ( VOUT - VINMIN ) VOUT x fSW x IL where VOUT is the voltage across the load and IOUT is the output current.
MAX16816
Input Capacitor
An input capacitor connected between V CC and ground must be used when configuring the MAX16816 as a buck converter. Use a low-ESR input capacitor that can handle the maximum input RMS ripple current. Calculate the maximum allowable RMS ripple using the following equation: IIN(RMS) = IOUT x VOUT x (VINMIN - VOUT ) VINMIN
where VINMIN is the minimum input voltage, VOUT is the output voltage, and fSW is the switching frequency. Buck-boost configuration: In a buck-boost converter the average inductor current is equal to the sum of the input current and the load current. In this case the inductance, L, is: L=
(VOUT + VINMIN ) x fSW x IL
Output Capacitor
VOUT x VINMIN
In most of the cases, an additional electrolytic capacitor should be added to prevent input oscillations due to line impedances. When using the MAX16816 in a boost or buck-boost configuration, the input RMS current is low and the input capacitance can be small (see the Typical Operating Circuits).
where VINMIN is the minimum input voltage, VOUT is the output voltage, and fSW is the switching frequency. The function of the output capacitor is to reduce the output ripple to acceptable levels. The ESR, ESL, and the bulk capacitance of the output capacitor contribute to the output ripple. In most of the applications, the output ESR and ESL effects can be dramatically reduced by using low-ESR ceramic capacitors. To reduce the ESL effects, connect multiple ceramic capacitors in parallel to achieve the required bulk capacitance. In a buck configuration, the output capacitance, CF, is calculated using the following equation: CF (VINMAX - VOUT ) x VOUT VR x 2 x L x VINMAX x fSW 2
Operating the MAX16816 Without the Dimming Switch
The MAX16816 can also be used in the absence of the dimming MOSFET. In this case, the PWM dimming performance is compromised but in applications that do not require dimming the MAX16816 can still be used. A short circuit across the load will cause the MAX16816 to disable the gate drivers and they will remain off until the input power is recycled.
Switching Power MOSFET Losses
When selecting MOSFETs for switching, consider the total gate charge, power dissipation, the maximum drain-to-source voltage, and package thermal impedance. The product of the MOSFET gate charge and RDS(ON) is a figure of merit, with a lower number signifying better performance. Select MOSFETs optimized for high-frequency switching applications.
where VR is the maximum allowable output ripple. In a boost configuration, the output capacitance, CF, is calculated as: CF (VOUT - VINMIN ) x 2 x IOUT VR x VOUT x fSW
Layout Recommendations
Typically, there are two sources of noise emission in a switching power supply: high di/dt loops and high dv/dt surfaces. For example, traces that carry the drain current often form high di/dt loops. Similarly, the heatsink of the MOSFET connected to the device drain presents a high dv/dt source; therefore, minimize the surface area of the heatsink as much as possible. Keep all PCB traces carrying switching currents as short as possible to minimize current loops. Use ground planes for best results.
where IOUT is the output current. In a buck-boost configuration, the output capacitance, CF, is calculated as: CF 2 x VOUT x IOUT VR x (VOUT + VINMIN ) x fSW
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23
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
Careful PCB layout is critical to achieve low switching losses and clean, stable operation. Use a multilayer board whenever possible for better noise performance and power dissipation. Follow these guidelines for good PCB layout: * Use a large copper plane under the MAX16816 package. Ensure that all heat-dissipating components have adequate cooling. Connect the exposed pad of the device to the ground plane. * Isolate the power components and high current paths from sensitive analog circuitry. * Keep the high-current paths short, especially at the ground terminals. This practice is essential for stable, jitter-free operation. Keep switching loops short. * Connect AGND, SGND, and QGND to a ground plane. Ensure a low-impedance connection between all ground points. * Keep the power traces and load connections short. This practice is essential for high efficiency. Use thick copper PCBs (2oz vs. 1oz) to enhance full-load efficiency. * Ensure that the feedback connection to FB is short and direct. * Route high-speed switching nodes away from the sensitive analog areas. * To prevent discharge of the compensation capacitors, C1 and C2, during the off-time of the dimming cycle, ensure that the PCB area close to these components has extremely low leakage. Discharge of these capacitors due to leakage may result in degraded dimming performance.
MAX16816
1-Wire Interface
EEPROM implementation uses a 1-Wire communication method. A 1-Wire net-based system consists of three main elements: a bus master with controlling software, the wiring and associated connectors, and 1-Wire devices. Data on the 1-Wire net is transferred with respect to time slots. For example, the master pulls the bus low and holds it for 15s or less to write a logic `1', and holds the bus low for at least 60s to write a logic `0'. During EEPROM programming the MAX16816 is a 1-Wire slave device only. Data and clock signals are supplied through FAULT.
MAX16816 1-Wire Function Commands
Table 10 shows the list of 1-Wire function commands for the MAX16816. Use these commands to start the programming mode, write to the on-chip EEPROM, and read EEPROM through the 1-Wire interface. PASS_CODE_ONE: The PASS_CODE_ONE sequence is the first code that the MAX16816 must receive from the master. PASS_CODE_ONE must be received within the initial 8ms programming window after startup. PASS_CODE_TWO: The PASS_CODE_TWO sequence is the second code that the MAX16816 must receive during the 8ms programming window. The MAX16816 will start searching for PASS_CODE_TWO only after PASS_CODE_ONE has been received. EXT_EEM_MODE: The EXT_EEM_MODE command clears the PASS_CODE_ONE and PASS_CODE_TWO verification register. Use this command to exit programming mode. SET_WRITE_EE: The SET_WRITE_EE command is the write all command for the MAX16816. When the device detects the SET_WRITE_EE command the write
Table 10. MAX16816 1-Wire Function Commands
COMMAND PASS_CODE_ONE PASS_CODE_TWO EXT_EEM_MODE SET_WRITE_EE SET_WRITE_SCH SET_READ_SCH DATA BIT CODE D7 0 0 0 0 ADD 0 D6 0 0 0 0 ADD 0 D5 1 0 0 0 ADD 0 D4 0 0 0 0 ADD 0 D3 1 1 0 0 DATA 0 D2 0 0 0 1 DATA 1 D1 0 0 0 0 DATA 1 D0 1 1 1 0 DATA 0 HEX CODE 29h 09h 01h 04h -- 06h
24
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
sequence begins. All EEPROM bits are copied to the EEPROM from the scratchpad with a single SET_WRITE_EE command. This command also sets an internal BUSY flag to mask all other incoming signals. SET_WRITE_SCH: The SET_WRITE_SCH command transfers data to the scratchpad. The 4 MSBs contain the register address and the 4 LSBs contain the data to be written. The internal BUSY flag is not set by this command. Table 11 shows the MAX16816 EEPROM memory organization. Use the SET_WRITE_EE command to transfer data from the scratchpad to the EEPROM. SET_READ_SCH: The SET_READ_SCH command is the command to read data in the scratch pad buffer. Once the MAX16816 receives the SET_READ_SCH command, data on the scratchpad register is shifted out. After 60 clock cycles, the MAX16816 completes the SET_READ_SCH sequence. The BUSY signal is not set by this command. programming purposes. Ensure that V CC is greater than the UVLO threshold because both UVEN and FAULT are pulled up to 5V. See the Electrical Characteristic tables for details.
MAX16816
VCC EN C READ UVEN
MAX16816
FAULT
DATA IN
Programming To program the MAX16816 on-chip EEPROM with a pulldown device, directly connect FAULT to the DATA IN input of a microcontroller (C). Also, connect FAULT to the DATA OUT output of a C using an external switch (Figure 5). Connect the EN of the C directly to UVEN to control the internal timer of the MAX16816 for
DATA OUT
WRITE
Figure 5. Programming Through a FAULT Pin
Table 11. MAX16816 Memory Map (Scratchpad)
SCRATCHPAD ADDRESS 1h 2h 3h 4h 5h 6h-9h Ah Bh Ch Dh Eh Fh EEPROM ADDRESS Reserved Reserved Reserved Reserved Reserved 14h-23h 24h-27h 28h-2Bh 2Ch-2Fh 30h-33h 34h-37h 38h-3Bh Reserved Reserved Reserved Reserved Reserved Reserved Binning Adjustment Register REG2 Control Register Reserved Blanking Time Adjustment Register Digital Soft-Start Duration Register, Internal Oscillator Enable Bit Slope Compensation Register REGISTER
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25
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
Programming Sequences The C (master) starts the communication with the MAX16816 by pulling UVEN high. The MAX16816 then does the handshaking with the C by pulling FAULT low. Once the C receives the handshaking signal, it begins the initialization sequences to reset the 1-Wire interface. The sequence consists of a reset pulse from the C followed by a presence pulse from the MAX16816. At this point the C must send PASS_CODE_ONE and PASS_CODE_TWO. These pass codes must be received by the MAX16816 within the 8ms programming slot to allow the MAX16816 to enter the EE programming mode. Initialization Procedure (Reset and Presence Pulses) All 1-Wire communication with the MAX16816 begins with an initialization sequence that consists of a Reset Pulse from the master followed by a Presence Pulse from the MAX16816 (Figure 6). When the MAX16816 sends the Presence Pulse in response to the Reset Pulse, it is indicating to the master that it is ready to receive and transmit data. During the initialization sequence, the bus master transmits the reset pulse by pulling the 1-Wire bus low for a minimum of 480s. The bus master then releases the bus and goes into receive mode. When the bus is released, the pullup resistor pulls the 1-Wire bus high. When the MAX16816 detects this rising edge, it waits 15s to 60s and then transmits a Presence Pulse by pulling the 1-Wire bus low for 60s to 240s. Read and Write Time Slots The bus master writes data to the MAX16816 during write time slots and reads data from the MAX16816 during read time slots. One bit of data is transmitted over the 1-Wire bus per time slot.
MAX16816
1-Wire Signaling
The MAX16816 requires strict protocols to ensure data integrity. The protocol consists of four types of signaling on one line: reset sequence with Reset Pulse and Presence Pulse, Write-Zero, Write-One, and Read-Data. Except for the Presence Pulse, the bus master initiates all falling edges. Externally pull FAULT below VIL to indicate a logic-input low. Release the pulldown device to indicate a logicinput high. The MAX16816 will pull FAULT low below VOL to indicate a logic-output low. FAULT is pulled high with an internal 10k resistor above VOH to indicate a logic-output high.
MASTER Tx "RESET PULSE" tMSP
MASTER Rx "PRESENCE PULSE"
VOH
VOL OR VIL 0V tRSTL
RESISTOR
MASTER
MAX16816
Figure 6. 1-Wire Initialization Timing
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
Write Time Slots There are two types of write time slots: Write-1 time slots and Write-0 time slots. The bus master uses a Write-1 time slot to write a logic `1' to the MAX16816 and a Write-0 time slot to write a logic `0'. All write time slots must be a minimum of 60s in duration with a minimum of a 1s recovery time between individual Write slots. Both types of write time slots are initiated by the master pulling the 1-Wire bus low (Figures 7 and 8). To generate a Write-1 time slot, the bus master must release the 1-Wire bus within 15s after pulling the bus
low. When the bus is released, the pullup resistor will pull the bus high. To generate a Write-0 time slot, the bus master must continue to hold the bus low for the duration of the time slot (at least 60s) after pulling the 1-Wire bus low. The MAX16816 samples the 1-Wire bus during a window that lasts from 15s to 60s after the master initiates the Write time slot. If the bus is high during the samples window, a `1' is written to the MAX16816. If the line is low, a `0' is written to the MAX16816.
MAX16816
tW1L VOH MAX16816 SAMPLING WINDOW VOL 0V tSLOT tREC
RESISTOR
MASTER
Figure 7. 1-Wire Write-1 Time Slot
tW0L VOH
MAX16816 SAMPLING WINDOW VIL 0V tREC tSLOT
RESISTOR
MASTER
Figure 8. 1-Wire Write-0 Time Slot
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming MAX16816
Read Time Slots The MAX16816 can only transmit data to the master when the master issues read time slots.
All read time slots must be a minimum of 60s in duration with a minimum of a 1s recovery time between slots. A read time slot is initiated by the master device pulling the 1-Wire bus low for a minimum of 1s and then releasing it (Figure 9). After the master initiates the read time slot, the MAX16816 will transmit a `1' or a `0' on the bus. The MAX16816 transmits a `1' by leaving the bus high and transmits a `0' by pulling the bus low. When transmitting a `0', the MAX16816 will release the bus before the end of the time slot, and the bus will be pulled back to its high idle state by the pullup resistor. Output data from the MAX16816 is valid for 15s after the falling edge that initiated the read time slot. Therefore, the master must release the bus and then sample the bus state within 15s from the start of the slot.
tMSR tRL VOH
MASTER SAMPLING WINDOW VIL / VOL 0V tSLOT tREC
RESISTOR
MASTER
MAX16816
Figure 9. 1-Wire Read Time Slot
28
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
Chip Information
PROCESS: BiCMOS
FAULT CLMP REG2 CS+ VCC CS-
Pin Configuration
TOP VIEW
MAX16816
32
N.C. UVEN REG1 AGND REF DIM RTSYNC CLKOUT
31
30
29
HI
28
27
26
25 24 23 22 21
N.C. DGT QGND SNSSNS+ DRI DRV SGND
1 2 3 4 5 6 7 8
+
MAX16816
LO
20 19
*EP
18 17
9
I.C.
10
I.C.
11
I.C.
12
COMP
13
CS
14
FB
15
OV
16
SGND
TQFN (5mm x 5mm)
*EP = EXPOSED PAD
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29
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming MAX16816
Typical Operating Circuits (continued)
VIN RCS RUV2 CCLMP CF
RUV1 UVEN CUVEN
VCC
CS+
DGT
CS-
LO
CLMP RD DRV SNS+ RSENSE QS LEDs
REF R3 DIM R4
MAX16816
SNSQGND ROV1 OV REG2 DRI HI ROV2
FAULT RTSYNC RT COMP R1 CS FB REG1 CREG1 AGND SGND
CREG2
C2 R2 C1 BOOST CONFIGURATION
30
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Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
Typical Operating Circuits (continued)
MAX16816
VIN
RCS RUV2 CCLMP CF
VCC HI FAULT RUV1 UVEN CUVEN
LO CLMP
CS- CS+ DGT RD DRV SNS+ RSENSE SNSQS LEDs
MAX16816
DIM DIM REG1 CREG1 RT RTSYNC COMP R1 CS FB AGND SGND REG2 DRI
QGND
OV
CREG2
C2 C1 R2
BUCK CONFIGURATION
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31
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming MAX16816
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
32
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QFN THIN.EPS
Programmable Switch-Mode LED Driver with Analog-Controlled PWM Dimming
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
MAX16816
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 33
(c) 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
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