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19-2761; Rev 0; 1/03
KIT ATION EVALU ABLE AVAIL
Ultra-High-Efficiency White LED Drivers
General Description Features
o Synchronous Step-Up Regulator Achieves >95% Efficiency Internal Switch and Synchronous Rectifier Eliminates External MOSFETs and Diodes 1MHz Fixed Frequency Minimizes Component Sizes o o o o Up to 90% Total LED Efficiency Accurate LED Current Matching (8% max) Adjustable Maximum LED Current Multimode Dimming Control Digital Pulse-Width Modulation Control 2-Bit Parallel Control 3-Bit Parallel Control Analog Control o Selectively Enable LEDs o Open-LED Detection o Unique 0.5mA LED Test Mode o 2.7V to 5.5V Input Supply Range o Small 4mm x 4mm 20-Pin Thin QFN Package
MAX1984/MAX1985/MAX1986
The MAX1984/MAX1985/MAX1986 are white light-emitting diode (LED) drivers that use individual regulators to control the current of up to eight LEDs. A high-efficiency step-up regulator generates just enough voltage to keep all the current regulators in regulation. A versatile dimming interface accommodates analog, digitally adjusted pulse-width modulation (DPWM), or parallel control. The individual current regulators allow good current matching between LEDs. Open or shorted LEDs cannot affect the performance of other LEDs. The step-up regulator achieves high efficiency by using synchronous rectification. The internal N-channel switch and P-channel synchronous rectifier eliminate the need for external MOSFETs and diodes. The 1MHz switching frequency allows the use of low-profile inductors and ceramic capacitors. The brightness can be easily adjusted using a multimode dimming interface, which allows brightness control through a DPWM signal, a 2- or 3-bit parallel control interface, or an analog signal. The DPWM signal can be connected directly to the control pin without the need for an external RC filter if its frequency is 10kHz or above. The MAX1984 drives up to eight LEDs, the MAX1985 drives up to six LEDs, and the MAX1986 drives up to four LEDs. Each device has an LED select pin (SEL) that allows one subset, the other subset, or all LEDs to be illuminated. All three devices are available in a 4mm 4mm thin QFN package.
Ordering Information
PART MAX1984ETP MAX1985ETP MAX1986ETE TEMP RANGE -40C to +85C -40C to +85C -40C to +85C PIN-PACKAGE 20 Thin QFN 20 Thin QFN 16 Thin QFN NO. OF LEDs 8 6 4
Applications
PDAs and Hand-Held PCs Cellular Phones Digital Cameras
Pin Configurations
MODE MODE BITC BITC SEL SEL SEL BITC 13 12 BITA 11 BITB 10 REF 9 SETI 5 LD2 6 LDG 7 LD3 8 LD4 BITA BITA
TOP VIEW
MODE 15
IN
IN
20 OUT 1 LX 2 GND 3 LD1 4 LD2 5 6 LD3
19
18
17
16 15 BITB 14 REF OUT 1 LX 2 GND 3 N.C. 4 LD1 5
20
19
18
17
16 15 BITB 14 REF OUT 1 LX 2
16
14
MAX1984
13 SETI 12 LD8 11 LD7
MAX1985
13 SETI 12 N.C. 11 LD6
MAX1986
GND 3 LD1 4
7 LD4
8 LDG
9 LD5
10 LD6
6 LD2
7 LD3
8 LDG
9 LD4
10 LD5
4mm x 4mm THIN QFN
4mm x 4mm THIN QFN
4mm x 4mm THIN QFN
________________________________________________________________ Maxim Integrated Products
IN
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Ultra-High-Efficiency White LED Drivers MAX1984/MAX1985/MAX1986
ABSOLUTE MAXIMUM RATINGS
OUT, IN, BITA, BITB, BITC, LD1, LD2, LD3, LD4, LD5, LD6, LD7, LD8 to GND ................................-0.3V to +6V LDG to GND........................................................................0.3V LX to GND ................................................-0.3V to (VOUT + 0.3V) SETI, REF, MODE, SEL to GND ...................-0.3V to (VIN + 0.3V) Continuous Power Dissipation (TA = +70C) 16-Pin Thin QFN (derate 16.9mW/C above +70C) ...1349mW 20-Pin Thin QFN (derate 16.9mW/C above +70C) ...1349mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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
(Circuit of Figure 1; VIN = 3.3V, SETI = BITA = BITB = BITC = SEL = IN, MODE = GND, COUT = 4.7F, CREF = 0.22F, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER IN Supply Range IN Undervoltage Lockout Threshold IN Quiescent Current IN Shutdown Current REF Output Voltage REF Line Regulation REF Load Regulation Oscillator Frequency Oscillator Maximum Duty Cycle OUT Overvoltage Protection (OVP) Threshold INTERNAL MOSFET SWITCHES N-Channel MOSFET On-Resistance N-Channel MOSFET Leakage Current P-Channel MOSFET On-Resistance P-Channel MOSFET Leakage Current N-Channel MOSFET Current Limit CONTROL INPUTS BITA, BITB, BITC Input Logic Low Level BITA, BITB, BITC Input Logic High Level MODE Input Logic Low Level MODE Input Logic High Level MODE, BITA, BITB, BITC Input Bias Current 2.7V < VIN < 5.5V 2.7V < VIN < 5.5V 2.7V < VIN < 5.5V 2.7V < VIN < 5.5V 2.7V < VIN < 5.5V VIN - 0.4 0.01 1 1.6 0.4 0.4 V V V V A ILX = 200mA VLX = 5.5V, BITA = BITB = BITC = GND ILX = 200mA LX = GND, VOUT = 5.5V, BITA = BITB = BITC = GND MAX1984 MAX1985 MAX1986 0.50 0.40 0.30 0.4 0.1 0.5 0.1 0.65 0.52 0.39 0.8 1 1 1 0.81 0.65 0.52 A A A VLD1 to VLD8 = 50mV, OUT rising, 100mV typical hysteresis 5.1 50mV typical hysteresis BITA = BITB = BITC = IN, LD1 to LD8 = GND BITA = BITB = BITC = GND IREF = 0 2.7V < VIN < 5.5V -1A < IREF < +50A 0.8 1.230 CONDITIONS MIN 2.7 2.2 2.4 400 0.1 1.250 0.2 5 1 85 5.3 5.5 TYP MAX 5.5 2.6 600 1 1.270 5 15 1.2 UNITS V V A A V mV mV MHz % V
2
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Ultra-High-Efficiency White LED Drivers
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1; VIN = 3.3V, SETI = BITA = BITB = BITC = SEL = IN, MODE = GND, COUT = 4.7F, CREF = 0.22F, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER SEL Input Logic Low Level SEL Input Logic Midlevel SEL Input Logic High Level SEL Input Bias Current 2.7V < VIN < 5.5V 2.7V < VIN < 5.5V 2.7V < VIN < 5.5V SEL = GND, current out of the pin SEL = IN, current into the pin VLD_ = 80mV, SETI = BITA = BITB = BITC = IN VLD_ = 80mV, RSETI = 278k 0.1%, BITA = BITB = BITC = IN LD1 to LD8 Output Current VLD_ = 80mV, RSETI = 1.8M 0.1%, BITA = BITB = BITC = IN VLD_ = 80mV, RSETI = 597k 0.1%, BITA = BITB = BITC = IN VLD1 = 1V, RSETI = 10k, BITA = BITB = BITC = IN SETI = GND LD1 to LD8 Regulation Voltage SETI High-Level Threshold (18mA LED Default Current) SETI Low-Level Threshold (0.5mA LED Default Current) SETI Output Current OUTPUT CURRENT SOURCE LD1 to LD8 On-Resistance LD1 to LD8 Current-Source Compliance LD1 to LD8 Leakage Current DIGITAL BRIGHTNESS CONTROL 2-Bit Control DAC LSB 3-Bit Control DAC LSB DPWM BRIGHTNESS CONTROL DPWM Input Supply Range DPWM Shutdown Duty Cycle MODE = BITC = IN BITC = GND 2.3 3 5 5.5 7 V % MODE = SETI = BITB = IN, BITA = BITC = GND (Note 2) SETI = BITC = IN, MODE = BITA = BITB = GND (Note 2) 26 7 33 14 39 21 % % VLD_ = 50mV, VOUT = 3.5V BITA = BITB = BITC = IN, 80mV < VLD_ < 1V (Note 1) BITA = BITB = BITC = GND 3 0.3 0.01 4 5 1 % A SETI = IN, ILX = 120mA (MAX1984), 110mA (MAX1985), 98mA (MAX1986) 2.7V < VIN < 5.5V 2.7V < VIN < 5.5V SETI = GND 0.42 80 VIN - 0.4 50 40 70 125 100 16.5 22.5 12.5 16.5 18 25 14 18 26 0.50 100 0.60 120 mV V mV A 0.50 2.05 5 10 19.5 27.5 15.5 19.5 CONDITIONS MIN TYP MAX 0.4 1.85 UNITS V V V A
MAX1984/MAX1985/MAX1986
FULL-SCALE LED CURRENT ADJUSTMENT
mA
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3
Ultra-High-Efficiency White LED Drivers MAX1984/MAX1985/MAX1986
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1; VIN = 3.3V, SETI = BITA = BITB = BITC = SEL = IN, MODE = GND, COUT = 4.7F, CREF = 0.22F, TA = -40C to +85C, unless otherwise noted.) (Note 3)
PARAMETER IN Supply Range IN Undervoltage Lockout Threshold IN Quiescent Current REF Output Voltage REF Line Regulation REF Load Regulation Oscillator Frequency OUT Overvoltage Protection Threshold INTERNAL MOSFET SWITCHES N-Channel MOSFET On-Resistance P-Channel MOSFET On-Resistance N-Channel MOSFET Current Limit CONTROL INPUTS BITA, BITB, BITC Input Logic Low Level BITA, BITB, BITC Input Logic High Level MODE Input Logic Low Level MODE Input Logic High Level SEL Input Logic Low Level SEL Input Logic Midlevel 2.7V < VIN < 5.5V 2.7V < VIN < 5.5V 2.7V < VIN < 5.5V 2.7V < VIN < 5.5V 2.7V < VIN < 5.5V 2.7V < VIN < 5.5V 0.50 2.05 16 22 11.5 15.5 0.42 20 28 16.0 20.0 0.60 mA VIN - 0.4 0.4 1.85 1.6 0.4 0.4 V V V V V V V VLD1 to VLD8 = 50mV, OUT rising, 100mV typical hysteresis ILX = 200mA ILX = 200mA MAX1984 MAX1985 MAX1986 0.50 0.40 0.30 50mV typical hysteresis BITA = BITB = BITC = IN, LD1 to LD8 = GND IREF = 0 2.7V < VIN < 5.5V -1A < IREF < +50A 0.8 5.1 1.230 CONDITIONS MIN 2.7 2.2 TYP MAX 5.5 2.6 600 1.270 5 15 1.2 5.5 UNITS V V A V mV mV MHz V
0.8 1.0 0.81 0.65 0.52
A
SEL Input Logic High Level 2.7V < VIN < 5.5V FULL-SCALE LED CURRENT ADJUSTMENT VLD_ = 80mV, SETI = BITA = BITB = BITC = IN VLD_ = 80mV, RSETI = 278k 1%, BITA = BITB = BITC = IN LD1 to LD8 Output Current VLD_ = 80mV, RSETI = 1.8M 1%, BITA = BITB = BITC = IN VLD_ = 80mV, RSETI = 697k 1%, BITA = BITB = BITC = IN SETI = GND
4
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Ultra-High-Efficiency White LED Drivers
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1; VIN = 3.3V, SETI = BITA = BITB = BITC = SEL = IN, MODE = GND, COUT = 4.7F, CREF = 0.22F, TA = -40C to +85C, unless otherwise noted.) (Note 3)
PARAMETER LD1 to LD8 Regulation Voltage SETI High-Level Threshold (18mA LED Default Current) SETI Low-Level Threshold (0.5mA LED Default Current) SETI Output Current OUTPUT CURRENT SOURCE LD1 to LD8 On-Resistance LD1 to LD8 Current-Source Compliance DIGITAL BRIGHTNESS CONTROL 2-Bit Control DAC LSB 3-Bit Control DAC LSB DPWM BRIGHTNESS CONTROL DPWM Input Supply Range DPWM Shutdown Duty Cycle MODE = BITC = IN BITC = GND 2.3 3 5.5 7 V % ILD_ = 25mA, VOUT = 3.5V BITA = BITB = BITC = IN, 80mV < VLD_ < 1V (Note 1) 4 8 % CONDITIONS SETI = IN, ILX = 120mA (MAX1984), 110mA (MAX1985), 98mA (MAX1986) 2.7V < VIN < 5.5V 2.7V < VIN < 5.5V SETI = GND MIN 80 VIN - 0.4 50 40 125 100 TYP MAX 120 UNITS mV V mV A
MAX1984/MAX1985/MAX1986
MODE = SETI = BITB = IN, BITA = BITC = GND SETI = BITC = IN, MODE = BITA = BITB = GND (Note 2)
26 7
39 21
% %
Note 1: Current variation is caused by the current source voltage changes. Note 2: Measurement is with respect to 100% of the programmed LED output current. Note 3: Specifications to -40C are guaranteed by design, not production tested.
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5
Ultra-High-Efficiency White LED Drivers MAX1984/MAX1985/MAX1986
Typical Operating Characteristics
(Circuit of Figure 1; VIN = 3.3V, SETI = IN, MODE = IN, TA = +25C, unless otherwise noted.)
STEP-UP REGULATOR EFFICIENCY vs. LED CURRENT (8 LEDs)
MAX1984/85/86 toc01
STEP-UP REGULATOR EFFICIENCY vs. LED CURRENT (6 LEDs)
MAX1984/85/86 toc02
STEP-UP REGULATOR EFFICIENCY vs. LED CURRENT (4 LEDs)
MAX1984/85/86 toc03
100
100
100
90 EFFICIENCY (%)
VIN = 3.6V VIN = 3.0V VIN = 4.2V
90 EFFICIENCY (%)
VIN = 3.6V VIN = 3.0V VIN = 4.2V
90 VIN = 3.6V EFFICIENCY (%) 80 VIN = 4.2V VIN = 3.0V
80
80
70
70
70
60
60
60
50 0 5 10 15 20 25 LED CURRENT (mA)
50 0 5 10 15 20 25 LED CURRENT (mA)
50 0 5 10 15 20 25 LED CURRENT (mA)
STEP-UP REGULATOR EFFICIENCY vs. INPUT VOLTAGE (25mA LED CURRENT)
MAX1984/85/86 toc04
STEP-UP REGULATOR EFFICIENCY vs. INPUT VOLTAGE (4mA LED CURRENT)
MAX1984/85/86 toc05
TOTAL EFFICIENCY vs. LED CURRENT (8 LEDs)
MAX1984/85/86 toc06
100
100
100
95 EFFICIENCY (%)
90 EFFICIENCY (%) 8 LEDs 6 LEDs
90 EFFICIENCY (%)
80
80
90 8 LEDs 6 LEDs 85 4 LEDs
70
70 VIN = 3.0V 60 VIN = 3.6V VIN = 4.2V TOTAL = 10 15
60
4 LEDs
i =1
VLEDi x ILEDi
20 25
INPUT_POWER
80 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V)
50 2.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V)
50 0 5 LED CURRENT (mA)
TOTAL EFFICIENCY vs. LED CURRENT (6 LEDs)
MAX1984/85/86 toc07
TOTAL EFFICIENCY vs. LED CURRENT (4 LEDs)
VIN = 3.0V VIN = 3.6V VIN = 4.2V 80
MAX1984/85/86 toc08
TOTAL EFFICIENCY vs. INPUT VOLTAGE (25mA LED CURRENT)
MAX1984/85/86 toc09
100 VIN = 3.6V 90 EFFICIENCY (%) VIN = 3.0V
100
100
90 EFFICIENCY (%)
90 EFFICIENCY (%)
80 VIN = 4.2V
80 8 LEDs 70 6 LEDs 4 LEDs 60
70
70
60 TOTAL = 50 0 5 10 15
i =1
VLEDi x ILEDi
20 25
60 TOTAL = 50 0 5 10 15
i =1
VLEDi x ILEDi
20 25
INPUT_POWER
INPUT_POWER 50 2.5 3.0 3.5 4.0 4.5 5.0 5.5
LED CURRENT (mA)
LED CURRENT (mA)
INPUT VOLTAGE (V)
6
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Ultra-High-Efficiency White LED Drivers
Typical Operating Characteristics (continued)
(Circuit of Figure 1; VIN = 3.3V, SETI = IN, MODE = IN, TA = +25C, unless otherwise noted.)
MAX1984/MAX1985/MAX1986
TOTAL EFFICIENCY vs. INPUT VOLTAGE (4mA LED CURRENT )
MAX1984/85/86 toc10
LED CURRENT vs. INPUT VOLTAGE
MAX9184/85/86 toc11
LED CURRENT MATCHING
MAX9184/85/86 toc12
100 90 EFFICIENCY (%) 80 70 60 50 40 2.5 3.0 3.5 4.0 4.5 5.0
26.0
26
LED CURRENT (mA)
LED CURRENT (mA)
25.5
25
25.0
24 LD1 TO LD8 23 RSETI = 278k 22 0 50 100 150 200 250 300 LD_VOLTAGE (mV)
8 LEDs 6 LEDs 4 LEDs
24.5 RSETI = 278k 24.0 5.5 2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
STARTUP WAVEFORMS
MAX1984/85/86 toc13
LED CURRENT vs. DPWM DUTY
MAX9184/85/86 toc14
MAXIMUM LED CURRENT vs. SETI RESISTANCE
MAX9184/85/86 toc15
5V 0
25
30 THEORETICAL 25
A
4V B 2V 0 100mA C D 0 100s/div A: BITA VOLTAGE, 5V/div B: OUT VOLTAGE, 2V/div C: INDUCTOR CURRENT, 100mA/div D: LD_ CURRENT, 20mA/div 0 0 20 0 20mA LED CURRENT (mA) 15
THEORETICAL
MAXIMUM LED CURRENT (mA)
20
ACTUAL 10 50kHz DPWM FREQUENCY
20
ACTUAL
5
15
RSETI = 278k 10 40 60 80 100 0 500 1000 1500 2000 DPWM DUTY (%) SETI RESISTANCE (k)
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7
Ultra-High-Efficiency White LED Drivers MAX1984/MAX1985/MAX1986
Pin Description
PIN MAX1984 1 2 3 -- 4 MAX1985 1 2 3 4, 12 5 MAX1986 1 2 3 -- 4 NAME OUT LX GND N.C. LD1 FUNCTION Step-Up Regulator Output. Bypass OUT to GND with a 4.7F capacitor. Inductor Connection. LX is connected to the drains of the internal N-channel and P-channel MOSFETs. Ground No Connection. Not internally connected. LED1 Cathode Connection. LD1 is the open-drain output of an internal current regulator for controlling the current through LED1. It is able to sink up to 25mA. If not used, connect LD1 to GND. LED2 Cathode Connection. LD2 is the open-drain output of an internal current regulator for controlling the current through LED2. It is able to sink up to 25mA. If not used, connect LD2 to GND. LED3 Cathode Connection. LD3 is the open-drain output of an internal current regulator for controlling the current through LED3. It is able to sink up to 25mA. If not used, connect LD5 to GND. LED4 Cathode Connection. LD4 is the open-drain output of an internal current regulator for controlling the current through LED4. It is able to sink up to 25mA. If not used, connect LD4 to GND. Common Ground Connection for Internal Current Regulators. Connect LDG to GND. LED5 Cathode Connection. LD5 is the open-drain output of an internal current regulator for controlling the current through LED5. It is able to sink up to 25mA. If not used, connect LD5 to GND. LED6 Cathode Connection. LD6 is the open-drain output of an internal current regulator for controlling the current through LED6. It is able to sink up to 25mA. If not used, connect LD6 to GND. LED7 Cathode Connection. LD7 is the open-drain output of an internal current regulator for controlling the current through LED7. It is able to sink up to 25mA. If not used, connect LD7 to GND. LED8 Cathode Connection. LD8 is the open-drain output of an internal current regulator for controlling the current through LED8. It is able to sink up to 25mA. If not used, connect LD8 to GND. Maximum LED Current Set Input. SETI sets the maximum current through each LED. Connect SETI to IN for a default maximum current of 18mA; connect SETI to GND for the 0.5mA LED test mode. Connect a resistor from SETI to GND to adjust the maximum current between 12mA to 25mA (see the Setting the Maximum LED Current section). 1.25V Reference Output. Bypass REF to GND with a minimum 0.22F ceramic capacitor. Brightness Control Input (Multimode): DPWM Mode: Leave unconnected for greater than 50kHz operation. Add a capacitor from BITB to ground for lower frequency operation. Analog Mode: Analog control signal input. 2- or 3-Bit Parallel Mode: Digital input. Least significant bit (LSB) for 2-bit mode.
5
6
5
LD2
6
7
7
LD3
7
9
8
LD4
8
8
6
LDG
9
10
--
LD5
10
11
--
LD6
11
--
--
LD7
12
--
--
LD8
13
13
9
SETI
14
14
10
REF
15
15
11
BITB
8
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Ultra-High-Efficiency White LED Drivers
Pin Description (continued)
PIN MAX1984 MAX1985 MAX1986 NAME FUNCTION Brightness Control Input (Multimode): DPWM Mode: DPWM control signal input. Analog Mode: Connect to IN. 2- or 3-Bit Parallel Mode: Digital input. Most significant bit (MSB). Brightness Control Input: DPWM Mode: Connect to IN. Analog Mode: Connect to IN. 2-Bit Parallel Mode: Connect to GND. 3-Bit Parallel Mode: Digital input (LSB). Input Supply. IN provides power to the internal control circuitry and MOSFET drivers. Bypass IN to GND with a minimum 0.1F ceramic capacitor. Brightness Control Mode Selection Input. Connect MODE and BITC to IN for DPWM control. Connect MODE, BITA, and BITC to IN for analog control. For 2-bit parallel control, connect MODE to IN and BITC to ground. For 3-bit parallel control, connect MODE to GND. LED Selection Input. Connect SEL to IN to turn on all LEDs. Connect SEL to ground to turn on only LED1-LED5 (MAX1984), LED1-LED4 (MAX1985), or LED1 to LED3 (MAX1986). Leave SEL unconnected or force to VIN/2 to turn on only LED6 to LED8 (MAX1984), LED3-LED6 (MAX1985), or LED4 (MAX1986).
MAX1984/MAX1985/MAX1986
16
16
12
BITA
17
17
13
BITC
18
18
14
IN
19
19
15
MODE
20
20
16
SEL
VIN 2.7V TO 5.5V C1 2 x 2.2F C2 0.1F L1 10H 3 GND REF 2 LX 18 IN OUT
14 C3 0.22F VIN 13
1
SETI
MAX1984
LD1
4
D1
LD2 16
5
D2
BITA
LD3
6
D3
15 BRIGHTNESS CONTROL
BITB
LD4
7
D4
17
BITC
LD5
9
D5
19
MODE
LD6
10
D6
LED SELECT
20
SEL
LD7
11
D7
8
LDG
LD8
12
D8 C4 2 x 2.2F
Figure 1. Standard Application Circuit of the MAX1984 _______________________________________________________________________________________ 9
Ultra-High-Efficiency White LED Drivers MAX1984/MAX1985/MAX1986
L VIN CIN IN
LX OUT COUT
FB
STEP-UP CONTROLLER
MAX1984 MAX1985 MAX1986
GND CURRENT SENSE
MIN
EN1 IREF EN2 IREF EN3 IREF EN4 IREF
LD1 LDG LD2 LDG LD3 LDG LD4 LDG LD5 LDG LD6 LDG LD7 LDG LD8 LDG
LD1
UVLO COMP
LD2
LD3
2.4V CREF REF
REF AND BIAS BLOCK
LD4
SHUTDOWN MODE DIMMING CONTROL BITA BITB BITC SETI RSETI EN7 IREF EN8 IREF LD7** DIMMING CONTROL BLOCK IREF EN5 IREF EN6 IREF LD5*
LD6*
LD8**
LED SELECT
SEL
LOGIC
EN [8:1]
LDG
*MAX1984 AND MAX1985 ONLY. **MAX1984 ONLY.
Figure 2. System Functional Diagram
10
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Ultra-High-Efficiency White LED Drivers
Standard Application Circuits
The standard application circuit of the MAX1984 drives eight white LEDs (Figure 1). The standard application circuit of the MAX1985 drives six white LEDs (Figure 6). The standard application circuit of the MAX1986 drives four white LEDs (Figure 7). The input voltage range is from 2.7V to 5.5V. Table 1 lists the recommended component options and Table 2 lists the component suppliers. 25mA LED current. The LED current is sensed using an internal 1 resistor connected between the source of the MOSFET and ground. The regulator controls the output current by comparing the voltage across the current-sense resistor with a reference voltage (IREF) set by the dimming control circuitry.
MAX1984/MAX1985/MAX1986
Startup and Feedback
The step-up converter is regulated at a voltage just high enough to power the LEDs. Since the forward voltage is different for each LED, the LED with the largest forward voltage sets the regulation voltage. Each current regulator's voltage drop (from LD_ to LDG) is monitored and the lowest voltage drop is used as the step-up regulator's feedback. At startup, it is important to ensure the output voltage rises high enough to forward bias all LEDs and allow their current regulators to detect their presence. Therefore, before the current regulators are enabled the step-up regulator output is made to rise up to the OUT OVP threshold (5.3V, typ). Then, the step-up regulator stops switching and each current regulator output is tested
Detailed Description
The MAX1984/MAX1985/MAX1986 are white LED drivers that use individual regulators to control the current of up to eight LEDs. A high-efficiency step-up regulator generates just enough voltage to keep all the current regulators in regulation. A versatile dimming interface accommodates analog, DPWM, or parallel control.
LED Current Regulators
Good LED current matching is achieved using individual current regulators for each LED (Figure 3). The regulator is an analog gain block with an open-drain N-channel MOSFET output stage and can sink up to
Table 1. Component List
DESIGNATION DESCRIPTION MAX1984 2 x 2.2F, 6.3V X5R ceramic capacitors (0603) Taiyo Yuden JMK107BJ225MA TDK C1608X5ROJ225K Surface-mount white LEDs Nichia NSCW215T 10H, 1A inductor Sumida CLS5D11HP-100NC 15H, 0.85A inductor Sumida CLS5D11HP-150NC 22H, 0.65A inductor Sumida CLS5D11HP-220NC MAX1985 2 x 2.2F, 6.3V X5R ceramic capacitors (0603) Taiyo Yuden JMK107BJ225MA TDK C1608X5ROJ225K MAX1986 2.2F, 6.3V X5R ceramic capacitors (0603) Taiyo Yuden JMK107BJ225MA TDK C1608X5ROJ225K
C1, C4
D1-D4, D5*, D6*, D7**, D8** L1
*MAX1984 and MAX1985 only. **MAX1984 only.
Table 2. Component Suppliers
SUPPLIER Nichia Sumida Taiyo Yuden TDK PHONE 717-285-2323 847-545-6700 800-348-2496 847-803-6100 FAX 717-285-9378 847-545-6720 847-925-0899 847-390-4405 WEBSITE www.nichia.com www.sumida.com www.t-yuden.com www.component.tdk.com
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11
Ultra-High-Efficiency White LED Drivers MAX1984/MAX1985/MAX1986
THRESHOLD
EN_ IREF
LD_
CURRENT SENSE SLOPE COMP OC COMP OSCILLATOR OSC SUMMING COMPARATOR LOGIC GATE DRIVERS
1 LDG
FB 100mV 5.3V OUT OV COMP
Figure 3. Current Regulator Functional Diagram
Figure 4. Step-Up Regulator Functional Diagram
for an LED's presence. The current regulators are enabled and any regulator with an output voltage less than 45mV is detected and is ignored, preventing outputs left open or shorted to ground from dominating the step-up regulation loop. Outputs shorted to IN, OUT, or any voltage above 45mV resemble valid LEDs and are regulated at the current set point. As the LEDs draw current, the step-up regulator's output voltage gradually falls and the voltage drop across each of the current regulators reduces. Eventually, the voltage drop across whichever current regulator drives the LED with the highest forward voltage reaches the step-up regulator's threshold (100mV, typ) and step-up switching starts again (see the Startup Waveform in the Typical Operating Characteristics).
MOSFET and turns on the P-channel MOSFET when one of the following three conditions occurs: the summing comparator output becomes high, the switch current exceeds the overcurrent threshold, or the falling edge of the oscillator occurs. Both the N-channel MOSFET and the P-channel MOSFET turn off if the output voltage exceeds the overvoltage rising threshold. Both switches stay off until all of the following three conditions are satisfied: the output voltage is below the overvoltage falling threshold, the summing comparator output is low, and the next rising edge of the oscillator occurs.
Brightness Control Interface
The light intensity of the white LEDs can be easily adjusted from 15% to 100% of the full-scale LED current chosen by SETI. The MAX1984/MAX1985/MAX1986 support DPWM control, analog control, and 2-bit or 3-bit parallel control. DPWM Control To use the DPWM control mode, connect MODE and BITC to IN, leave BITB unconnected, and connect the DPWM signal to BITA. The LED current is given by the following equation: ILED = D ILED(FS) where ILED(FS) is the full-scale LED current set by SETI, and D is the duty cycle of the DPWM signal. The average voltage of the DPWM signal is obtained through an internal RC filter (Figure 5). The 0.1ms filter time constant allows the use of DPWM frequencies from 10kHz to 2MHz. If lower frequencies are preferred, an external
Step-Up Regulator
The step-up regulator employs a fixed-frequency current-mode control method to generate the bias voltage for the white LEDs. The regulator takes the minimum value of all the LD_ pin voltages as the feedback signal to ensure that the output voltage is high enough to drive all the LEDs. The heart of the controller is a multiinput, open-loop comparator that sums three signals: the feedback error signal with respect to the 100mV reference, the current-sense signal, and the slope compensation ramp (Figure 4). In normal operation, the controller starts a new cycle by turning on the N-channel MOSFET and turning off the P-channel MOSFET on the rising edge of the internal oscillator if all of the following three conditions are satisfied: the summing comparator output is low, the switch current does not exceed the overcurrent threshold, and the output voltage does not exceed the overvoltage threshold. The controller turns off the N-channel
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Ultra-High-Efficiency White LED Drivers
capacitor can be connected from BITB to ground to increase the total time constant. Use the following equation to calculate the total time constant: = 0.2M CEXT + 0.098ms where CEXT is the external capacitance. The recommended DPWM duty-factor range is from 20% to 100% for DPWM frequencies between 20kHz and 2MHz, using the internal 0.1ms filter. For lower DPWM operating frequencies, use CEXT and ensure the voltage on C EXT (BITB), including ripple, remains above DFMIN 0.75 VREF, where DFMIN is the minimum reliable DPWM duty factor of 15%. In DPWM mode, the MAX1984/MAX1985/MAX1986 enter shutdown mode when the DPWM duty cycle is below 5% (typ) and BITC is a logical low level. Analog Control To use the analog control mode, connect MODE, BITA, and BITC to IN. Connect BITB to a DC voltage that sets the LED current. The operational range for the analog control is from 140mV (15%) to 0.75 VREF (100%). The LED current is given by the following equation: VBITB x ILED(FS) ILED = K1 + K2 x 0.75 x VREF where K1 = 0.0465, K2 = 0.953, VBITB is the voltage at the BITB pin, VREF is the 1.25V internal reference voltage, and ILED(FS) is the full-scale LED current set by SETI. In analog mode, the MAX1984/MAX1985/MAX1986 enter shutdown mode when both VBITA and VBITB are logic low. Parallel Control The MAX1984/MAX1985/MAX1986 also support 2-bit or 3-bit parallel control. To use the 3-bit parallel control mode, connect MODE to ground. BITA is the most significant bit and BITC is the least significant bit. To use the 2-bit parallel control, connect MODE to IN and BITC to ground. BITA is the most significant bit and BITB is the least significant bit. In parallel mode, the MAX1984/MAX1985/MAX1986 enter shutdown mode when BITA, BITB, and BITC are logic low. Tables 3 and 4 are the truth tables.
MAX1984/MAX1985/MAX1986
SHUTDOWN THRESHOLD MODE 0.75 x VREF BITA BITB BITC DECODER 3-BIT IREF 200k 9.8M 10pF 38 DAC 1 100 VIN
SHUTDOWN
0.75 x VREF LEVEL SHIFT
TO CURRENT REGULATORS
SETI 18mA DEFAULT SETI RSETI 300k VIN - 0.7V 0.045V 200k 7.2M SETI 0.5mA TEST
Figure 5. Brightness Control Equivalent Functional Diagram ______________________________________________________________________________________ 13
Ultra-High-Efficiency White LED Drivers MAX1984/MAX1985/MAX1986
LED Selection
The MAX1984/MAX1985/MAX1986 provide a control input (SEL) to selectively turn on one subset, the other subset, or all of the LEDs. SEL is a three-level logic input that can be connected to logic low, logic high, or left unconnected. Table 5 is the truth table.
Shutdown
As soon as the input voltage rises above the UVLO threshold and the internal reference is ready, the stepup regulator starts unless the device is in shutdown. If a 2-bit or 3-bit parallel control is used, the MAX1984/ MAX1985/MAX1986 enter shutdown mode when BITA, BITB, and BITC are logic low. The parts come out of shutdown if at least 1 bit is logic high. If DPWM control is used, the parts enter shutdown mode when the duty cycle of BITA is less than 5% (typ) and BITC is logic low. If analog control is used, the parts enter shutdown when the voltages on both BITA and BITB are logic low.
LED Test Mode
Connecting SETI to ground enables the LED test mode. In this mode, the LED current is set to 0.5mA and DC-to-DC switching is inhibited. OUT is powered from IN through an internal silicon diode. Forcing 0.5mA through the LED is a simple way to determine whether the diode has suffered any ESD damage. LEDs that do not light in this mode usually have suffered ESD or other damage. The dimming control inputs are ignored in the test mode.
Overvoltage Protection
Output OVP prevents the internal switches from being damaged if all LEDs are open. If the output voltage rises above OUT OVP rising threshold, the MAX1984/MAX1985/MAX1986 turn off the step-up regulator. Once the output voltage falls below OVP falling threshold, the step-up regulator turns on again.
Table 3. 3-Bit Parallel Control Truth Table
BITA 0 0 0 0 1 1 1 1 BITB 0 0 1 1 0 0 1 1 BITC 0 1 0 1 0 1 0 1 BRIGHTNESS (%) 0 14.3 26.6 42.9 57.1 71.4 85.7 100 COMMENTS Shutdown Minimum current -- -- -- -- -- Full-scale current set by SETI
Applications Information
Inductor Selection
The MAX1984/MAX1985/MAX1986's 1MHz switching frequency allows the use of low-profile surface-mount inductors. The MAX1984 works well with a 10H inductor, the MAX1985 works well with a 15H inductor, and the MAX1986 works well with a 22H inductor. The inductor saturation current rating should be higher than the N-channel switch current limit. For high efficiency, choose an inductor made of high-frequency core material to reduce core losses. Using a shielded inductor reduces radiated EMI.
Table 4. 2-Bit Parallel Control Truth Table
BITA 0 0 1 1 BITB BITC 0 1 0 1 0 0 0 0 BRIGHTNESS (%) 0 33.3 66.7 100 COMMENTS Shutdown Minimum current -- Full-scale current set by SETI
Output Capacitor Selection
The output capacitor affects the circuit's stability and output-voltage ripple. The MAX1984 works well with a 4.7F ceramic output capacitor, the MAX1985 works well with a 3.3F ceramic output capacitor, and the MAX1986 works well with a 2.2F ceramic output capacitor. Always use capacitors with working voltage ratings higher than the output OVP rising threshold (5.5V max).
Table 5. SEL Control Truth Table
SEL Low (VSEL < 0.4V) Mid (SEL unconnected or 0.5V < VSEL < 1.8V) High (VSEL > 2.05V) MAX1984 LED1 to LED5 ON LED6 to LED8 ON MAX1985 LED1 to LED4 ON LED5 to LED6 ON All LEDs ON MAX1986 LED1 to LED3 ON LED4 ON
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Ultra-High-Efficiency White LED Drivers
Input Capacitor Selection
The input capacitor reduces the current peaks drawn from the input supply and reduces noise injection into all devices running from that supply. The input voltage source impedance determines the required size of the input capacitor. The standard application circuits (Figures 1, 6, and 7) use an input capacitor equal to the output capacitor to accommodate the high impedance seen in a typical lab environment. Actual applications usually have much lower source impedance since the step-up regulator typically runs directly from a lowimpedance battery. Often, the input capacitor can be reduced by 50% or more of the output capacitor value. To prevent noise from coupling into the device, connect an additional 0.1F ceramic capacitor from the IN pin to the GND pin. Place that capacitor within 5mm of the pins.
PC Board Layout and Grounding
Careful PC board layout is very important for proper operation. Use the following guidelines for good PC board layout: 1) Minimize the area of high-current loops by placing the input capacitors, inductor, and output capacitors less than 0.2in (5mm) from the LX and GND pins. Connect these components with wide traces. Avoid using vias in the high-current paths. If vias are unavoidable, use many vias in parallel to reduce resistance and inductance. 2) Create islands for the analog ground and power ground. The analog ground island includes the exposed backside pad of the device, the REF bypass capacitor ground, and the SETI resistor ground. The power ground island includes the GND pin, the common ground for the current regulators (LDG), and the step-up regulator's input/output capacitor grounds. The analog ground and power ground islands are connected together at only one location using a short trace between the GND pin and the exposed backside pad underneath the device. 3) Maximize the width of the power ground traces to improve efficiency, and reduce output-voltage ripple and noise spikes. 4) Place the IN pin and REF pin bypass capacitors within 5mm to the device. 5) Minimize the size of LX node while keeping it wide and short to reduce radiated EMI. Refer to the MAX1985 evaluation kit for an example of proper board layout.
MAX1984/MAX1985/MAX1986
Setting the Maximum LED Current
The full-scale current through each LED can be set using SETI. When SETI is connected to IN, the full-scale LED current is set to the default value of 18mA. When SETI is connected to GND, the LED current is set to 0.5mA LED test mode. If SETI is connected with a resistor to GND, the full-scale LED current can be adjusted from 14mA to 25mA: ILED(FS) = 12mA + K x 0.75 x VREF RSETI
where K = 3851, and VREF is the internal reference voltage.
Chip Information
TRANSISTOR COUNT: 3016
______________________________________________________________________________________
15
Ultra-High-Efficiency White LED Drivers MAX1984/MAX1985/MAX1986
VIN 2.7V TO 5.5V C1 2 x 2.2F C2 0.1F L1 15H 3 GND 14 C3 0.22F VIN 13 REF 2 LX 18 IN OUT 1 3 GND D1 10 LD2 16 6 D2 C3 0.22F REF OUT 1 VIN 2.7V TO 5.5V C1 2 x 2.2F C2 0.1F L1 22H
2 LX
14 IN
SETI
MAX1985
LD1
5
BITA
LD3
7
D3 VIN 9 SETI
MAX1986
LD1
4
D1
LD2
5
D2
15 BRIGHTNESS CONTROL
BITB
LD4
9
D4 12 BITA LD3 7 D3
17
BITC
LD5
10
D5 11 BITB LD4 8 D4 C4 2 x 2.2F
19
MODE
LD6
11
D6 C4 2 x 2.2F
BRIGHTNESS CONTROL
13
BITC
LDG
6
LED SELECT
20
SEL
N.C.
4
15 8 LDG N.C. 12
MODE
SEL
16
LED SELECT
Figure 6. Standard Application Circuit of the MAX1985
Figure 7. Standard Application Circuit of the MAX1986
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Ultra-High-Efficiency White LED Drivers
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.)
24L QFN THIN.EPS
MAX1984/MAX1985/MAX1986
PACKAGE OUTLINE 12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
A
PACKAGE OUTLINE 12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
A
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 ____________________ 17 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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