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19-0847; Rev 0; 11/07
KIT ATION EVALU E AILABL AV
Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN
General Description
The MAX8822 drives up to four white light-emitting diodes (LEDs) with regulated constant current for display backlighting in cell phones, digital cameras, PDAs, and other handheld devices. By utilizing a proprietary negative 0.5x inverting charge pump and innovative independent low-dropout (LDO) adaptive current regulators, very high efficiency is achieved over the full 1-cell Li+ battery voltage range, even with large LED VF mismatch. The 1MHz fixed-frequency switching allows for tiny external components. The regulation scheme is optimized to ensure low EMI and low input ripple. Two 200mA, low-noise, high power-supply-rejection-ratio (PSRR) LDOs with programmable output voltages are included on-chip to provide power to camera modules or other devices. The MAX8822 features a single-wire, serial-pulse controllogic interface that programs LED current and the output voltages of the LDOs. The LED dimming range is pseudo-logarithmic from 24mA to 0.1mA in 31 steps. LDO output voltages are programmable in 16 different combinations to meet various camera module requirements. The MAX8822 includes soft-start, thermal shutdown, open- and short-circuit protection.
Features
High-Efficiency Charge Pump for Up to Four White LEDs Independent Adaptive Voltage Supply for Each LED 24mA to 0.1mA Dimming Range 1% (typ) Current Accuracy and 0.3% Current Matching Low 65A (typ) Quiescent Current Dual 200mA Low-Noise, High PSRR LDOs 16 Different Output Voltage Combinations Up to 3.3V High 60dB PSRR at 10kHz Flexible Single-Wire Control for Dimming and LDO Output Voltage Low 0.5A (typ) Shutdown Mode Soft-Start Limits Inrush Current Thermal Shutdown and Open- and Short-Circuit Protection Tiny 16-Pin, 3mm x 3mm Thin QFN Package (0.8mm max Height) with Exposed Paddle
MAX8822
Applications
White LED Backlighting Cell Phones and Smartphones
PART MAX8822ETE+
Ordering Information
PIN-PACKAGE 16 Thin QFN-EP* (3mm x 3mm) TOP MARK AFW PKG CODE T1633-5
Typical Operating Circuit
INPUT 2.7V TO 5.5V 1F 1F
Note: The device is specified over the -40C to +85C extended temperature range. +Denotes a lead-free package. *EP = Exposed paddle.
C2N
C1P
C1N
C2P
Pin Configuration
LDO1 LED2 10 LED1 LED3 9 8 7 LED4 NEG C1N C2N 6 5 1 IN 2 GND 3 C1P 4 C2P
LED1 IN 4.7F GND LED2
TOP VIEW
12 LDO2 13
UP TO 24mA/LED
11
MAX8822
LED3 LED4
ENLED 14
SERIALPULSE CONTROL INTERFACE ENLED NEG 2.2F ENLDO REF 0.1F LDO2 EP 1F VLDO1 VLDO2 1F
ENLDO 15 REF 16
MAX8822
LDO1
+
THIN QFN (3mm x 3mm)
________________________________________________________________ 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.
Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN MAX8822
ABSOLUTE MAXIMUM RATINGS
IN, C1N, C2N, REF, ENLED, ENLDO, LDO1, LDO2 to GND...............................................................-0.3V to +6.0V IN, REF, ENLED, ENLDO, LDO1, LDO2 to NEG ...............................................................-0.3V to +6.0V LED_, C1N, C2N to NEG .............................-0.3V to (VIN + 0.3V) C1P, C2P to GND ........................................-0.3V to (VIN + 0.3V) NEG to GND ..........................................................-6.0V to +0.3V NEG, LDO1, LDO2 Short-Circuit Current to GND ......Continuous Continuous Power Dissipation (TA = +70C) 16-Pin Thin QFN 3mm x 3mm (derate 14.7mW/C above +70C) .............................1177mW 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
(VIN = 3.6V, VGND = 0V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER IN Operating Voltage Undervoltage Lockout (UVLO) Threshold UVLO Hysteresis Shutdown Supply Current ENLED = ENLDO = GND TA = +25C TA = +85C VIN rising CONDITIONS MIN 2.7 2.25 2.45 100 0.5 0.5 65 1.4 160 20 VIN = 2.7V to 5.5V VIN = 2.7V to 5.5V VIL = 0V or VIH = 5.5V TA = +25C TA = +85C 2.5 0.5 0.5 100 2.5 1 0.5 (VIN - VNEG) (VNEG - 0.5 x VIN) / INEG All LEDs off, EN_ = GND 5 2.8 10 5.0 500 500 0.01 0.1 1.4 0.4 1 100 5 TYP MAX 5.5 2.65 UNITS V V mV A A mA C C V V A ms s s s ms MHz ms V k
IN Operating Supply Current
Charge pump inactive, ILED1 = ILED2 = ILED3 = ILED4 = 0.1mA Charge pump active, VIN = 2.7V, 1MHz switching, ILED1 = ILED2 = ILED3 = ILED4 = 0.1mA
Thermal-Shutdown Threshold Thermal-Shutdown Hysteresis SERIAL-PULSE CONTROL Logic Input-High Voltage (VIH) Logic Input-Low Voltage (VIL) Logic Input Current tSHDN tLO tHI tINIT tHOLD CHARGE PUMP Switching Frequency Soft-Start Time Charge-Pump Regulation Voltage Open-Loop NEG Output Resistance NEG Shutdown Discharge Resistance
See Figures 1 and 2 (Note 2) See Figures 1 and 2 See Figures 1 and 2 First high pulse from shutdown (Figures 1 and 2) Pulse width to latch EN_ count (Figures 1 and 2) (Note 3)
2
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Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 3.6V, VGND = 0V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER CURRENT REGULATOR (LED1-LED4) Programmable Current Range ILED_ = 24mA, TA = +25C Current Accuracy ILED_ = 24mA, TA = -40C to +85C ILED_ = 0.1mA, TA = +25C LED_ Dropout Voltage LED_ Current Regulator Switchover Threshold (Inactive to Active) LED_ Current Regulator Switchover Hysteresis LED_ Shutdown Leakage Current LDO_ Output Current Current Limit LDO1 Dropout Voltage LDO2 Dropout Voltage Line Regulation Load Regulation Power-Supply Rejection VOUT/VIN Output Noise Voltage (RMS) All LEDs off, ENLED = GND (Note 5) VLDO = 0V ILDO1 = 200mA, VLDO1 = 2.8V (Notes 5 and 6) ILDO2 = 200mA, VLDO2 = 2.8V (Notes 5 and 6) 3.4V VIN < 5.5V, ILDO = 100mA 50A < ILDO < 200mA 10Hz to 10kHz, CLDO = 1F, ILDO = 30mA 100Hz to 100kHz, CLDO = 1F, ILDO = 30mA ENLDO count = 5 LDO1 Output Voltage ILDO1 = 100mA (Note 7) ENLDO count = 6, 13 ENLDO count = 1, 3, 7, 9, 14 ENLDO count = 2, 4, 8, 15 ENLDO count = 1, 2 LDO2 Output Voltage ILDO2 = 100mA (Note 7) ENLDO count = 3, 4, 10 ENLDO count = 5, 6, 7, 8, 11 ENLDO count = 9, 12 Ground Current Shutdown Output Impedance ILDO = 500A ENLDO = GND 1.746 2.716 TA = +25C TA = +85C 200 220 150 300 1 0.1 60 45 1.2 1.8 2.800 3.3 1.2 1.5 1.800 2.8 50 1 A k 1.854 V 2.884 V 750 250 550 ILED_ = 24mA (Note 4) Charge pump inactive Charge pump active 125 0.1 -2 -3 5 60 80 150 120 250 175 mV 1 24.0 +2 +3 % mA CONDITIONS MIN TYP MAX UNITS
MAX8822
VLED_ falling
mV
100 0.01 0.1 5
mV A
mA mA mV mV mV/V mV/mA dB VRMS
Note 1: Note 2: Note 3: Note 4: Note 5: Note 6:
Limits are 100% production tested at TA = +25C. Specifications over the operating temperature range are guaranteed by design. Hold EN_ low for at least 2.5ms to guarantee shutdown. Hold EN_ high for at least 2.5ms to latch EN count. LED dropout voltage is defined as the LED_ to GND voltage when current into LED_ drops 10% from the value at VLED = 0.5V. Guaranteed by design, not production tested. LDO dropout voltage is defined as VIN - VOUT when VOUT has dropped 100mV below the initial value of VOUT when VIN = VOUT + 0.8V. Note 7: LDO output voltage corresponds to the LDO output voltage programmed by pulsing ENLDO low by the given count and then holding ENLDO high for greater than tHOLD to set the voltage value. See Figure 2. _______________________________________________________________________________________ 3
Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN MAX8822
Typical Operating Characteristics
(VIN = 3.6V, VEN_ = VIN, Circuit of Typical Operating Circuit, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. SUPPLY VOLTAGE (4 MATCHED WLEDs)
MAX8822 toc01
EFFICIENCY vs. SUPPLY VOLTAGE (4 MISMATCHED WLEDs)
MAX8822 toc02
EFFICIENCY vs. SUPPLY VOLTAGE (4 MISMATCHED WLEDs)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 6.4mA/LED 20.8mA/LED
MAX8822 toc03
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 2.7 3.0 3.3 3.6 VIN FALLING 3.9 6.4mA/LED 1.6mA/LED 20.8mA/LED 14.4mA/LED
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VIN FALLING 2.7 3.0 3.3 3.6 3.9 1.6mA/LED 14.4mA/LED
100
10 0 2.7 3.0 3.3 3.6
VIN FALLING 3.9 4.2
4.2
4.2
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
EFFICIENCY vs. Li+ BATTERY VOLTAGE (4 MATCHED WLEDs)
MAX8822 toc04
EFFICIENCY vs. Li+ BATTERY VOLTAGE (4 MISMATCHED WLEDs)
MAX8822 toc05
EFFICIENCY vs. Li+ BATTERY VOLTAGE (4 MISMATCHED WLEDs)
MAX8822 toc06
100 20mA/LED 90 EFFICIENCY (%) 80 70 6.4mA/LED 60 50 40 4.2 3.9 3.8 3.7 3.6 14.4mA/LED
100 90 EFFICIENCY (%) 80 70 1.6mA/LED 60 50 40 14.4mA/LED
100 90 EFFICIENCY (%) 80 20.8mA/LED 70 60 50 40 6.4mA/LED
1.6mA/LED
3.5 3.4 3.0
4.2 3.9
3.8
3.7
3.6
3.5 3.4 3.0
4.2 3.9
3.8
3.7
3.6
3.5 3.4 3.0
Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED)
Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED)
Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED)
SUPPLY CURRENT vs. SUPPLY VOLTAGE (4 WLEDs)
MAX8822 toc07
SUPPLY CURRENT vs. SUPPLY VOLTAGE (RGB MODULE)
RGB MODULE: LUMEX SML-LX3632SISUGSBC, VIN FALLING 20.8mA/LED
MAX8822 toc08
INPUT VOLTAGE RIPPLE vs. SUPPLY VOLTAGE (4 WLEDs)
2.8 INPUT VOLTAGE RIPPLE (mVRMS) 2.4 2.0 1.6 1.2 0.8 0.4 0 6.4mA/LED 2.7 3.0 3.3 3.6 3.9 4.2 14.4mA/LED 20.8mA/LED VIN FALLING, MISMATCHED LEDs
MAX8822 toc09
140 120 SUPPLY CURRENT (mA) 100
VIN FALLING MISMATCHED LEDs
100
80 SUPPLY CURRENT (mA)
20.8mA/LED 80 60 40 20 0 2.7 3.0 3.3 3.6 3.9 4.2 SUPPLY VOLTAGE (V) 14.4mA/LED
60
14.4mA/LED
40 6.4mA/LED 20 1.6mA/LED 0 2.7 3.0 3.3 3.6 3.9 4.2 SUPPLY VOLTAGE (V)
6.4mA/LED 1.6mA/LED
SUPPLY VOLTAGE (V)
4
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Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN
Typical Operating Characteristics (continued)
(VIN = 3.6V, VEN_ = VIN, Circuit of Typical Operating Circuit, TA = +25C, unless otherwise noted.)
LED CURRENT MATCHING vs. SUPPLY VOLTAGE
16.8 16.6 LED CURRENT (mA) 16.4 16.2 16.0 15.8 15.6 15.4 15.2 15.0 2.7 3.1 3.5 3.9 16mA/LED, VIN FALLING 4.3 4.7 5.1 5.5 4 LEDs, 24mA/LED, VIN = 3.8V 400ns/div ILED1 24mA (AC-COUPLED) 10mA/div IIN 100mA (AC-COUPLED) 10mA/div
MAX8822 toc10
MAX8822
TYPICAL OPERATING WAVEFORMS (CHARGE PUMP INACTIVE)
MAX8822 toc11
17.0
VIN
10mV/div (AC-COUPLED)
SUPPLY VOLTAGE (V)
TYPICAL OPERATING WAVEFORMS (CHARGE PUMP ACTIVE)
MAX8822 toc12
STARTUP AND SHUTDOWN
MAX8822 toc13
VENLED VIN 10mV/div (AC-COUPLED) VIN
5V/div 0V 24mV/div (AC-COUPLED)
IIN
100mA (AC-COUPLED) 10mA/div IIN 100mA/div 0A ILED_TOTAL 1ms/div ILED_ = 24mA 100mA/div 0A 24mA (AC-COUPLED) 10mA/div 4 LEDs, 24mA/LED, VIN = 3.2V 400ns/div
ILED1
SERIAL-PULSE CONTROL DIMMING RESPONSE
MAX8822 toc14
SERIAL-PULSE CONTROL LDO VOLTAGE PROGRAMMING
MAX8822 toc15
VENLED 24mA
5V/div 7 PULSES 0V VENLDO 14.4mA 10mA/div
0
5V/div 8 PULSES 1.8V 1V/div
ILED1
0A
ILDO2
0V 3.3V
IIN 4 LEDs 1ms/div
50mA/div 0A
2V/div ILDO1 ILDO1 = ILDO2 = 100mA 400s/div 0V
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5
Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN MAX8822
Typical Operating Characteristics (continued)
(VIN = 3.6V, VEN_ = VIN, Circuit of Typical Operating Circuit, TA = +25C, unless otherwise noted.)
LINE-TRANSIENT RESPONSE (NO MODE CHANGE)
MAX8822 toc16
LINE-TRANSIENT RESPONSE (MODE CHANGE)
MAX8822 toc17
VIN 3.7V IIN
4.2V 500mV/div (AC-COUPLED) 100mA/div 0mA
VIN 3.4V
3.8V 500mV/div (AC-COUPLED) 100mA/div 0mA
IIN
ILED_TOTAL
100mA/div 0mA ILED_ = 24mA 1ms/div
ILED_TOTAL ILED_ = 24mA 1ms/div
100mA/div 0mA
LDO1 LOAD TRANSIENT
MAX8822 toc18
LDO2 LOAD TRANSIENT
MAX8822 toc19
VLDO1
20mV/div (AC-COUPLED)
VLDO2
20mV/div (AC-COUPLED)
150mA 50mA/div ILDO1 VLDO1 = 2.8V 20s/div 20s/div 10mA ILDO2 VLDO2 = 1.8V
150mA 50mA/div 10mA
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
MAX8822 toc20
LDO OUTPUT NOISE
MAX8822 toc21
80 70 60 PSRR (dB) 50 40 30 20 10 0 0.01 0.1 1 10 100 IOUT = 10mA COUT = 1F
50V/div
VLDO = 2.8V, ILDO = 28mA 1000 400s/div FREQUENCY (kHz)
6
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Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN
Pin Description
PIN 1 2 3 4 5 6 7 NAME IN GND C1P C2P C2N C1N NEG FUNCTION Supply Voltage Input. Bypass IN to GND with a 4.7F ceramic capacitor placed as close as possible to the IC. The input voltage range is 2.7V to 5.5V. Ground. Connect to system ground. GND is used for charge-pump switching currents. Transfer Capacitor 1 Positive Connection. Connect a 1F ceramic capacitor from C1P to C1N. Transfer Capacitor 2 Positive Connection. Connect a 1F ceramic capacitor from C2P to C2N. Transfer Capacitor 2 Negative Connection. Connect a 1F ceramic capacitor from C2P to C2N. Transfer Capacitor 1 Negative Connection. Connect a 1F ceramic capacitor from C1P to C1N. Charge-Pump Output. Bypass NEG to GND with a 2.2F ceramic capacitor placed as close as possible to the IC. LED Current Regulators. Connect LED_ to the cathodes of the external LEDs. LED_ is high impedance in shutdown. Connect any unused LED_ to IN to disable the corresponding current regulator. LED_ current is programmed by pulsing ENLED as described in the LED Dimming Control section. LDO1 Output. Bypass LDO1 to GND with a 1F ceramic capacitor placed as close as possible to the IC. The LDO1 and LDO2 output voltage combination is selected by pulsing ENLDO low. See the LDO1/LDO2 Output Voltage Control section. LDO2 Output. Bypass LDO2 to GND with a 1F ceramic capacitor placed as close as possible to the IC. The LDO1 and LDO2 output voltage combination is selected by pulsing ENLDO low. See the LDO1/LDO2 Output Voltage Control section. WLED Enable and Dimming Control Input. Pulse ENLED low to program LED_ current. Hold ENLED low for at least 2.5ms to place the LED drivers in shutdown. See the LED Dimming Control section. LDO Enable and Voltage Control Input. Pulse ENLDO low to program the output voltage of both LDO1 and LDO2 to one of sixteen different combinations. Hold ENLDO low for at least 2.5ms to place the LDOs in shutdown. See the LDO1/LDO2 Output Voltage Control section. Reference. Bypass REF to GND with a 0.1F ceramic capacitor placed as close as possible to the IC. VREF regulates to 1.2V (typ). Exposed Paddle. Connect EP to GND. For good thermal dissipation, solder the exposed paddle to the power ground plane.
MAX8822
8-11
LED4-LED1
12
LDO1
13
LDO2
14
ENLED
15
ENLDO
16 --
REF EP
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7
Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN MAX8822
1 ENLED tHOLD 2.5ms 22.4mA 20.8mA 19.2mA 19.2mA ILED_ 4.8mA SHDN 2 3 4 1 2 3 13 14 tINIT = 120s tHI = 500ns TO 500s tLO = 500ns TO 500s tINIT INTERNAL CURRENT SHDN SETTING tHI tLO tHOLD 2.5ms 24.0mA 22.4mA 20.8mA 5.6mA 4.8mA tSHDN 2.5ms SHDN
24.0mA
SHDN
Figure 1. Timing Characteristics for LED Serial-Pulse Control Interface
0 ENLDO
1
2
3
1
2
3
12
13 tINIT = 120s tHI = 500ns TO 500s tLO = 500ns TO 500s
t INIT INTERNAL LDO1 SETTING INTERNAL LDO2 SETTING
tHOLD 2.5ms tHI tLO
tHOLD 2.5ms 2.8V 0V 1.8V
tSHDN 2.5ms SHDN
SHDN 0V
2.8V
3.3V
2.8V
2.8V
3.3V
SHDN 0V
1.2V
1.2V
1.5V 2.8V
1.2V
1.2V
1.5V
2.8V
0V
1.8V VLDO1 SHDN 1.5V SHDN 0V SHDN SHDN
VLDO2
Figure 2. Timing Characteristics for LDO Serial-Pulse Control Interface
Detailed Description
The MAX8822 drives up to four white LEDs (WLEDs) with regulated constant current for display backlighting in cell phones, cameras, PDAs, and other handheld devices. The IC also includes two low-noise, high-PSRR, 200mA LDOs for powering camera modules or other devices. Figure 3 depicts the MAX8822 block diagram. The MAX8822 IC utilizes a 0.5x inverting charge pump and extremely low-dropout current regulators to achieve high efficiency over the full 1-cell Li+ battery
voltage range. The charge pump remains inactive unless the LED current regulators require additional voltage to prevent them from entering dropout. To maximize efficiency, the current regulators operate with as little as 150mV voltage drop. Additionally, each LED current regulator is independently monitored and switched, ensuring the least possible power consumption to extend battery life (see the Adaptive Current Regulator Switchover section for details).
8
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Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN MAX8822
C3 1F C4 1F C5 2.2F
VIN IN INPUT 2.7V TO 5.5V C1 4.7F GND
C1P
C1N
C2P
C2N
NEG
NEG LDO1
0.5x INVERTING CHARGE PUMP LDO2
C6 1F C7 1F
REF C2 0.1F BANDGAP REF
LOW-DROPOUT LINEAR REGULATORS UVLO, THERMAL SHUTDOWN SEL MIN
ENLDO SERIALPULSE CONTROL INTERFACE ENLED
LDO VOLTAGE CONTROL
LED CURRENT CONTROL
NEG VIN
LED1 D1
INDEPENDENT, ADAPTIVE CURRENT REGULATORS
LED2
D2
LED3
D3
LED4
D4
MAX8822
EP
Figure 3. MAX8822 Functional Block Diagram and Application Circuit
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9
Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN MAX8822
MAX8822
LED CURRENT CONTROL NEG VIN LED CURRENT CONTROL
MAX8822
NEG VIN
ILED_ LED_
ILED_ LED_
CURRENT REGULATOR
VLED_ > SWITCHOVER THRESHOLD
CURRENT REGULATOR
VLED_ < SWITCHOVER THRESHOLD
Figure 4. Current Regulator Returning to GND
Figure 5. Current Regulator Returning to NEG
The LED current and LDO output voltages are programmed using a serial-pulse control interface. Pulse ENLED low (as discussed in the LED Dimming Control section) to decrease the LED current from 24mA to 0.1mA, or hold ENLED low for at least 2.5ms to place the LED current regulators in shutdown mode. LED dimming is controlled in 31 pseudo-logarithmic steps. Pulse ENLDO low (as discussed in the LDO1/LDO2 Output Voltage Control section) to choose LDO1 and LDO2 output voltages from one of 16 combinations including off. Drive both ENLED and ENLDO low for at least 2.5ms to place the IC in low-power (0.5A typ) shutdown mode. The MAX8822 includes soft-start, thermal shutdown, and open- and short-circuit protection.
LED Dimming Control
The MAX8822 uses a serial-pulse control interface to program the intensity of the LEDs. The dimming range is pseudo-logarithmic from 24mA to 0.1mA in 31 steps. All active LED current regulators are programmed to the same value, with a 1% (typ) current accuracy and 0.3% current matching between regulators. To program the LED current, pulse ENLED (500ns to 500s pulse width), as shown in Figure 1. An internal register accumulates the pulse count on the rising edge of the ENLED pulse. See Table 1 for the LED current values and the corresponding ENLED pulse count. Once the desired pulse count is met, hold ENLED high for at least 2.5ms (tHOLD) to internally latch the pulse-count value and enable the LED_ current at the programmed level. If ENLED is pulsed more than 31 times before latching, the pulse count restarts at 1 on the 32nd rising edge. To program a new LED current level, follow the previous sequence from the beginning. Drive ENLED low for greater than 2.5ms (typ) to place the LED current regulators in shutdown. When the MAX8822 starts up with ENLED high, the LEDs turn on at full brightness. If dimming control is not required, ENLED works as a simple on/off logic control. Drive ENLED high for at least 2.5ms to enable the LED current regulators, or drive ENLED low for at least 2.5ms for shutdown. The LED drivers operate at 100% brightness and off under these conditions.
Adaptive Current Regulator Switchover
When VIN is higher than the forward voltage of an LED plus the 150mV (typ) dropout voltage of the current regulator, the LED current returns through GND (Figure 4). If this condition is satisfied for all four WLEDs, the charge pump remains inactive. When VIN drops such that the current regulator voltage (VLED_) cannot be maintained above the dropout voltage for any of the individual LEDs, the charge pump activates and generates a voltage on NEG that is no greater than 5V (typ) below VIN. For any current regulator that is detected at the switchover threshold voltage of 150mV (typ, VIN falling), internal circuitry switches that current regulator's return path from GND to NEG to provide enough voltage across that regulator to overcome dropout (Figure 5). When VLED_ rises to 250mV (typ), the return of that current regulator is switched back from NEG to GND. Each current regulator is independently monitored to detect when switchover is required. Since the LED current is switched for only the individual LED current regulators requiring higher voltage, power consumption is minimized.
10
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Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN MAX8822
Table 1. ENLED Pulse Count and Programmed LED_ Current
ENLED PULSE COUNT* 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 PROGRAMMED LED_ CURRENT (mA) 24.0 22.4 20.8 19.2 17.6 16.0 14.4 12.8 11.2 9.6 8.0 6.4 5.6 4.8 4.0 3.2 ENLED PULSE COUNT* 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31** -- PROGRAMMED LED_ CURRENT (mA) 2.8 2.4 2.0 1.6 1.4 1.2 1.0 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 --
*Rising edge. **If ENLED is pulsed more than 31 times, the pulse count restarts at 1 on the 32nd rising edge.
Low LED Current Levels
The MAX8822 internally generates a PWM signal to obtain higher resolution at lower currents. As LED current is set below 6.4mA, the IC adjusts not only LED DC current, but the duty cycle is controlled by the PWM signal. The frequency of the PWM dimming signal is set at 1kHz with a minimum duty cycle of 1/16 to avoid the LED flickering effect to human eyes. Table 2 shows the current level and the corresponding duty cycle.
Table 2. Internal PWM Duty Cycle vs. LED Set Current
DUTY CYCLE (n/16th) 16 14 12 10 16 14 12 10 16 14 ILED (mA) 6.4 5.6 4.8 4.0 3.2 2.8 2.4 2.0 1.6 1.4 DUTY CYCLE (n/16th) 12 10 8 7 6 5 4 3 2 1 ILED (mA) 1.2 1.0 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
LDO1/LDO2 Output Voltage Control
Similar to the LED dimming control structure, the MAX8822 uses serial-pulse control to program the output voltages of LDO1 and LDO2 to one of sixteen different combinations. To program the LDO voltages, pulse ENLDO low (500ns to 500s pulse width), as shown in Figure 2. An internal register accumulates the pulse count on the rising edge of the ENLDO pulse. An initial pulse (tINIT) is required to enable the LDOs from shutdown. See Table 3 for LDO voltage combinations and the corresponding ENLDO pulse count. When the desired pulse count is met, hold ENLDO high for at least 2.5ms (tHOLD) to internally latch the pulse-count value and program the LDO output voltages at the desired level. If ENLDO is pulsed for more than 15 counts, LDO1 and LDO2 are off when the count is
latched (the count does not roll over). To program new LDO_ output voltages, follow the previous sequence from the beginning. Do not include the initial tINIT pulse when programming LDO voltages unless enabling the LDOs from shutdown (the OFF setting is not shutdown). Pulling ENLDO low for greater than 2.5ms places the LDOs in shutdown.
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Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN MAX8822
Table 3. ENLDO Pulse Count and LDO1 and LDO2 Output Voltage Selection
ENLDO PULSE COUNT* 0** 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15*** PROGRAMMED LDO1 VOLTAGE (V) 0 2.8 3.3 2.8 3.3 1.2 1.8 2.8 3.3 2.8 0 0 0 1.8 2.8 3.3 PROGRAMMED LDO2 VOLTAGE (V) 0 1.2 1.2 1.5 1.5 1.8 1.8 1.8 1.8 2.8 1.5 1.8 2.8 0 0 0
has cooled by 20C (typ) and resets the LEDs and LDOs in the default condition of I LED_ = 24mA and VLDO1 = VLDO2 = 0V.
Power-Up LED Short Detection and Open-Fault Protection
The MAX8822 contains special circuitry to detect an LED_ short-circuit condition at startup only, and disables that current regulator to avoid wasting battery power. If an LED fails short-circuit detection after startup, that current regulator continues current-regulated operation until IC power is cycled and the short circuit is detected during the subsequent startup. An open-circuit LED failure drives the voltage on the corresponding LED current-regulator output below the switchover threshold, enabling the charge pump.
Applications Information
Input Ripple
For LED drivers, input ripple is more important than output ripple. The amount of input ripple depends on the source supply's output impedance. Add a lowpass filter to the input of the MAX8822 to further reduce input ripple. Alternatively, increasing CIN reduces input ripple.
Using Fewer Than Four LEDs
The MAX8822 can operate with fewer than four LEDs. Disable the unused current regulator by connecting LED_ to IN. If an unused LED_ is not connected to IN, the MAX8822 operates as if an open LED has been detected. In this condition, the open-circuit LED_ drives the voltage on the corresponding output below the switchover threshold, enabling the charge pump.
*Rising edge. **Initial pulse is only required to enable LDOs from shutdown. ***If ENLDO is pulsed for more than 15 counts,VLDO1 and VLDO2 are 0V (not shutdown) when the count is latched (the count does not roll over).
Shutdown Mode
The MAX8822 features a shutdown mode to reduce power consumption. Hold ENLED low for at least 2.5ms to place the LEDs in shutdown. LED shutdown pulls NEG to GND through a 10k internal resistor. Hold ENLDO low for at least 2.5ms to place the LDOs in shutdown. LDO shutdown pulls LDO_ to GND through a 1k internal resistor. The MAX8822 consumes only 0.5A of supply current when both the LED current regulators and LDOs are in shutdown mode.
Component Selection
Ceramic capacitors are recommended due to their small size, low cost, and low ESR. Select ceramic capacitors that maintain their capacitance over temperature and DC bias. Capacitors with X5R or X7R temperature characteristics generally perform well. Recommended values are shown in the Typical Operating Circuit. Using a larger value input capacitor helps to reduce input ripple (see the Input Ripple section). The LDO output capacitor size affects LDO stability. A 1F ceramic capacitor is recommended to maintain stability for load currents up to 200mA.
LDO and LED Thermal Shutdown
The MAX8822 includes two thermal-limit circuits that protect the IC from temperatures exceeding +160C (typ). The first circuit monitors the internal LED_ regulator temperature and shuts down the entire IC when the temperature limit is violated. The second circuit monitors the internal LDO temperature and shuts down only the LDOs when the temperature limit is violated. The thermal-shutdown condition clears after temperature
12
PCB Layout and Routing
The MAX8822 is a high-frequency switched-capacitor voltage regulator. For best circuit performance, use a solid ground plane and place all capacitors as close as possible to the IC. Use large traces for the powersupply inputs to minimize losses due to parasitic trace
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Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN
resistance and to route heat away from the device. The exposed paddle lowers the thermal resistance of the package by providing a direct-heat conduction path from the die to the printed circuit board (PCB). Connect the exposed paddle to the GND plane directly under the IC, but do not rely on EP for ground functions. For good thermal dissipation, solder the exposed paddle to the power ground plane. Refer to the MAX8822 evaluation kit data sheet for an example PCB layout.
Chip Information
PROCESS: BiCMOS
MAX8822
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Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN MAX8822
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.)
12x16L QFN THIN.EPS
L
MARKING
E E/2
(ND - 1) X e
(NE - 1) X e
D2/2
D/2 D
AAAA
C L
e D2
k
b E2/2
0.10 M C A B
C L
L
E2
0.10 C
0.08 C A A2 A1 L
C L
C L
e
e
PACKAGE OUTLINE 8, 12, 16L THIN QFN, 3x3x0.8mm
21-0136
I
1 2
14
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Ultra-Efficient Negative Charge-Pump LED Driver with Dual LDOs in 3mm x 3mm Thin QFN
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.)
MAX8822
PKG REF. A b D E e L N ND NE A1 A2 k 0.25 0 0.35
8L 3x3 MIN. NOM. MAX. 0.70 0.25 2.90 2.90 0.75 0.30 3.00 3.00 0.55 8 2 2 0.02 0.20 REF 0.25 0.05 0 0.80 0.35 3.10 3.10 0.75
12L 3x3 MIN. NOM. MAX. 0.70 0.20 2.90 2.90 0.45 0.75 0.25 3.00 3.00 0.50 BSC. 0.55 12 3 3 0.02 0.20 REF 0.25 0.05 0 0.65 0.30 0.80 0.30 3.10 3.10
16L 3x3 MIN. NOM. MAX. 0.70 0.20 2.90 2.90 0.75 0.25 3.00 3.00 0.40 16 4 4 0.02 0.20 REF 0.05 0.80 0.30 3.10 3.10 0.50 PKG. CODES TQ833-1 T1233-1 T1233-3 T1233-4 T1633-2 T1633F-3 T1633FH-3 T1633-4 T1633-5
EXPOSED PAD VARIATIONS
D2 MIN. 0.25 0.95 0.95 0.95 0.95 0.65 0.65 0.95 0.95 NOM. 0.70 1.10 1.10 1.10 1.10 0.80 0.80 1.10 1.10 MAX. 1.25 1.25 1.25 1.25 1.25 0.95 0.95 1.25 1.25 MIN. 0.25 0.95 0.95 0.95 0.95 0.65 0.65 0.95 0.95 E2 NOM. 0.70 1.10 1.10 1.10 1.10 0.80 0.80 1.10 1.10 MAX. 1.25 1.25 1.25 1.25 1.25 0.95 0.95 1.25 1.25 PIN ID 0.35 x 45 0.35 x 45 0.35 x 45 0.35 x 45 0.35 x 45 0.225 x 45 0.225 x 45 0.35 x 45 0.35 x 45 JEDEC WEEC WEED-1 WEED-1 WEED-1 WEED-2 WEED-2 WEED-2 WEED-2 WEED-2
0.65 BSC.
0.50 BSC.
NOTES: 1. 2. 3. 4. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. N IS THE TOTAL NUMBER OF TERMINALS. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.20 mm AND 0.25 mm FROM TERMINAL TIP. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS . DRAWING CONFORMS TO JEDEC MO220 REVISION C. MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY. NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY. WARPAGE NOT TO EXCEED 0.10mm.
5. 6. 7. 8. 9. 10. 11. 12.
PACKAGE OUTLINE 8, 12, 16L THIN QFN, 3x3x0.8mm
21-0136
I
2 2
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 ____________________ 15
(c) 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
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