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19-0790; Rev 0; 4/07
Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN
General Description
The MAX8647/MAX8648 drive up to six white LEDs or two sets of RGB LEDs with regulated constant current for display backlight and fun light applications. By utilizing an inverting charge pump and extremely lowdropout adaptive current regulators, these ICs achieve very high efficiency over the full 1-cell Li+ battery voltage range and even with large LED forward voltage mismatch. The 1MHz fixed-frequency switching allows for tiny external components. The regulation scheme is optimized to ensure low EMI and low input ripple. The MAX8647/MAX8648 include thermal shutdown, openand short-circuit protection. The MAX8647 features an I 2C serial port, while the MAX8648 features a three-wire serial-pulse logic interface. Both devices support independent on/off and dimming for main and subbacklights. The dimming ranges are pseudo-logarithmic from 24mA to 0.1mA and off in 32 steps. Both devices include a temperature derating function to safely allow bright 24mA full-scale output current setting while automatically reducing current to protect LEDs at high ambient temperatures above +60C. The MAX8647/MAX8648 are available in a 16-pin, 3mm x 3mm thin QFN package (0.8mm max height).
KIT ATION EVALU BLE AVAILA
Features
Six Adaptive Current Regulators Independent Voltage Supply for Each LED Individual LED Brightness Control (MAX8647) 24mA to 0.1mA Dimming Range I2C Interface (MAX8647) Serial-Pulse Dimming Logic (MAX8648) 2% Accuracy, 0.4% Matching (typ) Low 70A Quiescent Current Low 1A Shutdown Current Inrush Current Limit TA Derating Function Protects LEDs 16-Pin, 3mm x 3mm Thin QFN Package
MAX8647/MAX8648
Ordering Information
PART DIMMING PIN PACKAGE TOP MARK AFD AFE PKG CODE T1633-5 T1633-5
MAX8647ETE+ I2C interface 16 Thin QFN-EP* MAX8648ETE+ Serial-pulse 16 Thin QFN-EP* logic
Applications
White LED Backlighting, Single or Dual Display Wide-Gamut RGB LED Display Backlighting Camera Flash or RGB Indicators Cellular Phones and Smartphones PDAs, Digital Cameras, and Camcorders
Note: All devices are specified over the -40C to +85C extended temperature range. +Denotes a lead-free package. *EP = Exposed paddle.
Typical Operating Circuit
1F 1F
Pin Configuration
LED2 LED4 LED3 LED5
C1P INPUT 2.7V TO 5.5V 1F GND
C1N
C2P
C2N NEG
1F
TOP VIEW
IN EP WHITE OR RGB LED
12 LED1 13 SDA (ENC) 14 SCL (ENB) 15 VDD (ENA) 16
11
10
9 8 7 LED6 NEG C1N C2N
MAX8648
LED1 LED2
D1 D2 D3 D4 D5 D6
MAX8647ETE MAX8648ETE +
1 IN 2 GND 3 C1P 4 C2P
6 5
ENA SERIALPULSE INTERFACE ENB ENC
LED3 LED4 LED5 LED6
THIN QFN
( ) DESIGNATE PINS ON THE MAX8648
________________________________________________________________ Maxim Integrated Products
1
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Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN MAX8647/MAX8648
ABSOLUTE MAXIMUM RATINGS
VDD, IN, SCL, SDA, ENA, ENB, ENC to GND........-0.3V to +6.0V VDD, IN, SCL, SDA, ENA, ENB, ENC to NEG ........-0.3V to +6.0V NEG to GND .............................................................-6V to +0.3V C2N to GND .............................................................-6V to +0.3V C1P, C2P to GND .......................................-0.3V to (VIN + 0.3V) C2P to C1N ..................................................-0.3V to (VIN + 0.3V) LED_, C1N, C2N to NEG .............................-0.3V to (VIN + 0.3V) Continuous Power Dissipation (TA = +70C) 16-Pin Thin QFN 3mm x 3mm (derate 20.8mW/C above +70C).............................................................1667mW 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
(VVDD = VIN = 3.6V, VGND = 0V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER IN Operating Voltage VDD Operating Voltage Undervoltage-Lockout (UVLO) Threshold Undervoltage-Lockout Hysteresis IN Shutdown Supply Current (All Outputs Off) VDD Shutdown Supply Current VSCL = VSDA = VDD (MAX8647), VEN_ = 0V (MAX8648) TA = +25C TA = +85C Charge pump inactive, two LEDs enabled at 0.1mA setting IN Operating Supply Current Charge pump active, 1MHz switching, all LEDs enabled at 0.1mA setting Charge pump inactive, two LEDs enabled at 0.1mA setting, TA = +25C Charge pump active, 1MHz switching, all LEDs enabled at 0.1mA setting, TA = +85C TA = +25C TA = +85C VIN rising CONDITIONS MIN 2.7 1.7 2.35 2.45 100 0.4 0.4 0.1 0.1 70 1.6 0.1 0.1 +160 20 0.7 x VDD 0.3 x VDD 50 -1 0.01 0.1 +1 C C 1.0 A 100 1.0 2.5 TYP MAX 5.5 5.5 2.55 UNITS V V V mV A A A mA
VDD Operating Supply Current
Thermal-Shutdown Threshold Thermal-Shutdown Hysteresis I2C INTERFACE (MAX8647) Logic-Input High Voltage (SDA, SCL) Logic-Input Low Voltage (SDA, SCL) Filtered Pulse Width (tSP) Logic-Input Current (SDA, SCL) VDD = 1.7V to 5.5V, hysteresis = 0.2 x VDD (typ) VDD = 1.7V to 5.5V, hysteresis = 0.2 x VDD (typ) VIN = 2.7V to 5.5V, VDD = 1.7V to 5.5V (Note 2) VIL = 0V or VIH = 5.5V TA = +25C TA = +85C
V V ns A
2
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Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN
ELECTRICAL CHARACTERISTICS (continued)
(VVDD = VIN = 3.6V, VGND = 0V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER SDA Output Low Voltage I2C Clock Frequency Bus Free Time Between START and STOP (tBUF) Hold Time Repeated START Condition (tHD_STA) SCL Low Period (tLOW) SCL High Period (tHIGH) Setup Time Repeated START Condition (tSU_STA) SDA Hold Time (tHD_DAT) SDA Setup Time (tSU_DAT) Setup Time for STOP Condition (tSU_STO) Logic-Input High Voltage Logic-Input Low Voltage Logic-nput Current tSHDN (Figure 3) tLO (Figure 3) tHI (Figure 3) Initial tHI (Figure 3) CHARGE PUMP Switching Frequency Soft-Start Time Charge-Pump Regulation Voltage Open-Loop NEG Output Resistance NEG Discharge Resistance in Shutdown or When the Charge Pump is Inactive LED1-LED6 CURRENT REGULATOR Current Setting Range Through an I2C or serial-pulse interface VLED_ = 0.5V for charge-pump inactive, VLED_ = -0.9V, VNEG_ = -1.4V 24mA setting, TA = +25C 24mA setting, TA = -40C to derating function start temperature (Note 2) 1.6mA setting, TA = +25C 0.1 -2 -5 -15 5 1 24.0 +2 +5 +15 % mA (VIN - VNEG) (VNEG - 0.5 x VIN) / INEG All LEDs off, EN_ = GND 4.3 1 0.5 5.0 2.5 10 5 MHz ms V k First EN_ high pulse (Note 2) (Note 2) (Note 2) (Note 2) (Note 2) (Note 2) (Note 2) (Note 2) 1.3 0.6 1.3 0.6 0.6 0 100 0.6 0.1 0.2 0.2 0.1 -0.01 50 0.1 CONDITIONS ISDA = 3mA, for acknowledge (Note 2) MIN TYP 0.03 MAX 0.40 400 UNITS V kHz s s s s s s ns s
MAX8647/MAX8648
SERIAL-PULSE LOGIC (EN_) (MAX8648) VIN = 2.7V to 5.5V VIN = 2.7V to 5.5V VIL = 0V or VIH = 5.5V TA = +25C TA = +85C 1 1 120 -1 0.01 0.1 4 500 1.4 0.4 +1 V V A ms s s s
Time from EN_ held low to ILED_ = 0mA
Current Accuracy
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Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN MAX8647/MAX8648
ELECTRICAL CHARACTERISTICS (continued)
(VVDD = VIN = 3.6V, VGND = 0V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Derating-Function Start Temperature Derating-Function Slope LED_ RDSON LED_ Dropout LED_ Current Regulator Switchover Threshold (Inactive to Active) LED_ Current Regulator Switchover Hysteresis LED_ Leakage in Shutdown All LEDs off TA = +25C TA = +85C From derating-function start temperature Not utilizing the charge pump Utilizing the charge pump 24mA setting (Note 3) VLED_ falling Not utilizing the charge pump Utilizing the charge pump 125 CONDITIONS MIN TYP +60 -2.5 3 4 60 90 150 100 0.01 0.1 5 120 200 175 MAX UNITS C %/C mV mV mV A
Note 1: Limits are 100% production tested at TA = +25C. Specifications over the operating temperature range are guaranteed by design. Note 2: Guaranteed by design. Note 3: LED dropout voltage is defined as the LED_ to GND voltage at which current into LED_ drops 10% from the value at VLED_ = 0.5V.
Typical Operating Characteristics
(VIN = 3.6V, VEN_ = VIN, circuit of Figure 1, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. SUPPLY VOLTAGE (DRIVING SIX MATCHED LEDs)
MAX8647/48 toc01
EFFICIENCY vs. Li+ BATTERY VOLTAGE (DRIVING SIX MATCHED LEDs)
MAX8647/48 toc02
EFFICIENCY vs. SUPPLY VOLTAGE (DRIVING SIX LEDs)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 LEDs HAVE MISMATCHED VF 2.7 3.0 3.3 3.6 3.9 4.2 16mA/LED 1.6mA/LED
MAX8647/48 toc03
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 2.7 3.0 3.3 3.6 3.9 1.6mA/LED 20.8mA/LED 16mA/LED 6.4mA/LED
100 90 EFFICIENCY PLED/PBATT (%) 80 70 1.6mA/LED 60 50 40 16mA/LED 6.4mA/LED 20.8mA/LED
100
0 4.2 3.9 3.8 3.7 3.6 3.5 3.4 3.0 Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED)
4.2
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
4
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Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN
Typical Operating Characteristics (continued)
(VIN = 3.6V, VEN_ = VIN, circuit of Figure 1, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. SUPPLY VOLTAGE (DRIVING SIX LEDs)
MAX8647/48 toc04
MAX8647/MAX8648
EFFICIENCY vs. Li+ BATTERY VOLTAGE (DRIVING SIX LEDs)
16mA/LED 90 EFFICIENCY PLED/PBATT (%) 80 70 1.6mA/LED 60 50
MAX8647/48 toc05
EFFICIENCY vs. Li+ BATTERY VOLTAGE (DRIVING SIX LEDs)
MAX8647/48 toc06
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 2.7 LEDs HAVE MISMATCHED VF 6.4mA/LED 20.8mA/LED
100
100 90 EFFICIENCY PLED/PBATT (%) 80 6.4mA/LED 70 60 50 20.8mA/LED
40 3.0 3.3 3.6 3.9 4.2 INPUT VOLTAGE (V)
LEDs HAVE MISMATCHED VF 4.2 3.9 3.8 3.7 3.6 3.5 3.4 3.0
40
LEDs HAVE MISMATCHED VF 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)
INPUT CURRENT vs. INPUT VOLTAGE (DRIVING SIX LEDs)
MAX8647/48 toc07
INPUT CURRENT vs. Li+ BATTERY VOLTAGE (DRIVING SIX LEDs)
MAX8647/48 toc08
INPUT CURRENT vs. INPUT VOLTAGE (RGB MODULE)
RGB MODULE: LUMEX SML-LX3632SISUGSBC ILED = 20.8mA ILED = 16mA 90 80 INPUT CURRENT (mA) 70 60 50 40 30 20 10 0 ILED = 1.6mA ILED = 4.8mA
MAX8647/48 toc09 MAX8647/48 toc12
200 180 160 INPUT CURRENT (mA) 140 120 100 80 60 40 20 0 2.7 3.2 3.7 ILED = 1.6mA ILED = 16mA LEDs HAVE MISMATCHED VF ILED = 6.4mA ILED = 20.8mA
200 180 160 INPUT CURRENT (mA) 140 120 100 80 60 40 20 0
LEDs HAVE MISMATCHED VF
100
20.8mA/LED 16mA/LED
6.4mA/LED 1.6mA/LED 4.2 3.9 3.8 3.7 3.6 3.5 3.4 3.0
4.2
2.7
3.2
3.7
4.2
INPUT VOLTAGE (V)
Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED)
INPUT VOLTAGE (V)
INPUT CURRENT vs. Li+ BATTERY VOLTAGE (RGB MODULE)
MAX8647/48 toc10
INPUT RIPPLE VOLTAGE vs. SUPPLY VOLTAGE (DRIVING SIX WHITE LEDs)
14 12 10 8 6.4mA/LED 6 4 2 0 1.6mA/LED 2.7 3.2 3.7 4.2 LEDs HAVE MISMATCHED VF 20.8mA/LED 16mA/LED
MAX8647/48 toc11
LED CURRENT MATCHING vs. INPUT VOLTAGE (16mA/LED)
17.0 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 4.3 4.7 5.1 5.5
100 90 80 INPUT CURRENT (mA) 70 60 50 40 30 20 10 0
RGB MODULE: LUMEX SML-LX3632SISUGSBC 20.8mA/LED 16mA/LED
16 INPUT RIPPLE VOLTAGE (mVRMS)
6.4mA/LED 1.6mA/LED 4.2 3.9 3.8 3.7 3.6 3.5 3.4 3.0
Li+ BATTERY VOLTAGE (V, TIME-WEIGHTED)
SUPPLY VOLTAGE (V)
INPUT VOLTAGE (V)
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Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN MAX8647/MAX8648
Typical Operating Characteristics (continued)
(VIN = 3.6V, VEN_ = VIN, circuit of Figure 1, TA = +25C, unless otherwise noted.)
1x MODE OPERATING WAVEFORMS (VIN = 4V)
MAX8647/48 toc14 MAX8647/48 toc13
LED CURRENT vs. TEMPERATURE
30 25 LED CURRENT (mA) 20
1.5x MODE OPERATING WAVEFORMS (VIN = 3V)
MAX8647/48 toc15
VIN
AC-COUPLED VIN 100mV/div IIN
AC-COUPLED 100mV/div 100mA/div
15 10 5 0 -40 -15 10 35 60 85
IIN
100mA/div 0A 20mA/div 0A 20mA/div ILED ALL LEDs ON ILED = 24mA 400ns/div 0A
ILED
ALL LEDs ON ILED = 24mA 400ns/div
0A
TEMPERATURE (C)
STARTUP AND SHUTDOWN (MAX8648)
MAX8647/48 toc16
SINGLE-WIRE PULSE DIMMING (MAX8648)
MAX8647/48 toc17
ENA = ENB = ENC VEN_
2V/div
VEN_ OPERATING IN 1x MODE, ALL 6 LEDs OPERATING
5V/div
VIN
AC-COUPLED 20mV/div
IIN
200mA/div 0A
TOTAL ILED5 20mA/div
ILED5
2V/div 0A 1ms/div 10ms/div 0A
LINE-TRANSIENT RESPONSE (VIN = 4.3V TO 3.8V TO 4.3V)
MAX8647/48 toc18
LINE-TRANSIENT RESPONSE WITH MODE CHANGE (VIN = 3.8V TO 3.4V TO 3.8V)
MAX8647/48 toc19
4.3V VIN 3.8V VIN 3.8V 3.4V
IIN
200mA/div 0A 24mA 20mA/div
IIN
200mA/div 0mA
ILED6
ILED6
24mA 20mA/div
1ms/div
1ms/div
6
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Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN
Pin Description
PIN MAX8647 1 MAX8648 1 NAME FUNCTION Supply Voltage Input. The input voltage range is 2.7V to 5.5V. Bypass IN to GND with a 1F ceramic capacitor as close as possible to the IC. IN is high impedance during shutdown. Connect IN to the anodes of all the LEDs. Ground. Connect GND to system ground and the input bypass capacitor as close as possible to the IC. 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. An internal 10k resistor pulls C2N to GND during shutdown. Transfer Capacitor 1 Negative Connection. Connect a 1F ceramic capacitor from C1P to C1N. Charge-Pump Negative Output. Connect a 1F ceramic capacitor from NEG to GND. In shutdown, an internal 10k resistor pulls NEG to GND. Connect the exposed paddle to NEG directly under the IC. LED Current Regulators. Current flowing into LED_ is based on the internal registers. Connect LED_ to the cathodes of the external LEDs. LED_ is high impedance during shutdown. For the MAX8647, program any unused LED_ to off and LED_ can be shorted to ground or left unconnected. For the MAX8648, short any unused LED_ to IN prior to power-up to disable the corresponding current regulator. I2C Data Input. Data is read on the rising edge of SCL. I2C Clock Input. Data is read on the rising edge of SCL. Logic-Input Supply Voltage. Connect to the supply voltage driving SDA and SCL. Bypass VDD to GND with a 0.1F ceramic capacitor. Enable and Serial-Pulse Dimming Control. ENA controls LED1, LED2, and LED3. ENB controls LED4 and LED5. ENC controls LED6. Drive EN_ logic-high to turn on the IC and enable the corresponding LED_ at 24mA each. Drive an individual EN_ logic-low for greater than 4ms to turn off the corresponding-current regulators or drive all three EN_ low to place the IC in shutdown. See the Serial-Pulse Dimming Control (MAX8648) section. Exposed Paddle. Connect to NEG.
MAX8647/MAX8648
IN
2 3 4 5 6
2 3 4 5 6
GND C1P C2P C2N C1N
7
7
NEG
8-13
8-13
LED6-LED1
14 15 16
-- -- --
SDA SCL VDD
--
14, 15, 16
ENC, ENB, ENA
--
--
EP
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Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN MAX8647/MAX8648
Detailed Description
The MAX8647/MAX8648 have an inverting charge pump and six current regulators capable of 24mA each to drive six white LEDs or two sets of RGB LEDs. The current regulators are matched to within 0.4% (typ) providing uniform white LED brightness for LCD backlight applications. To maximize efficiency, the current regulators operate with as little as 0.15V voltage drop. Individual white LED current regulators conduct current to GND or NEG to extend usable battery life. In the case of mismatched forward voltage of white LEDs, only the white LEDs requiring higher voltage are switched to pull current to NEG instead of GND, further raising efficiency and reducing battery current drain. used. Figure 2 shows a timing diagram for the I2C protocol. The MAX8647 is a slave-only device, relying upon a master to generate a clock signal. The master (typically a microprocessor) initiates data transfer on the bus and generates SCL to permit data transfer. A master device communicates with the MAX8647 by transmitting the proper 8-bit address (0x9A) followed by the 8-bit control byte. Each 8-bit control byte consists of a 3-bit command code and 5 bits of data (Table 1). Each transmit sequence is framed by a START (A) condition and a STOP (L) condition (Figure 2). Each word transmitted over the bus is 8 bits long and is always followed by an ACKNOWLEDGE CLOCK PULSE (K). The power-on default settings for D4 to D0 are all 0, which indicates that all LED_ are off.
Current-Regulator Switchover
When V IN is higher than the forward voltage of the white LED plus the 0.15V headroom of the current regulator, the LED current returns through GND. If this condition is satisfied for all six white LEDs, the charge pump remains inactive. When the input voltage drops so that the current-regulator headroom cannot be maintained for any of the individual white LEDs, the inverting charge pump activates and generates a voltage on the NEG pin that is no greater than 5V below VIN. Each current regulator contains circuitry that detects when it is in dropout and switches that current-regulator return path from GND to NEG. Since this is done on an LEDby-LED basis, the LED current is switched for only the individual LED requiring higher voltage, thus minimizing power consumption.
Serial-Pulse Dimming Control (MAX8648)
When the LEDs are enabled by driving EN_ high, the MAX8648 ramps LED current to 24mA. Dim the LEDs by pulsing EN_ low (1s to 500s pulse width). Each pulse reduces the LED current based on the LED dimming table, Table 3. After the current reaches 0.1mA, the next pulse restores the current to 24mA. Figure 3 shows a timing diagram for EN_. ENA controls LED1, LED2, and LED3. ENB controls LED4 and LED5. ENC controls LED6. If dimming control is not required, EN_ work as simple 100% brightness or off controls. Drive EN_ high to enable the LEDs, or drive EN_ low to disable. The IC is shutdown when all three EN_ are low for 4ms or longer.
Low LED Current Levels
The MAX8647/MAX8648 internally generate a PWM signal to obtain higher resolution at lower currents. See Single-Wire Pulse Dimming in the Typical Operating Characteristics section. As the ILED setting is below 6.4mA, the IC adjusts not only ILED 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 flicking effect to human eyes. Table 1 shows the current level and the corresponding duty cycle.
Table 1. Internal PWM Duty Cycle vs. LED Set Current
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/16) 16 14 12 10 16 14 12 10 16 14 ILED (mA) 1.2 1.0 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 DUTY CYCLE (n/16) 12 10 8 7 6 5 4 3 2 1
I2C Interface (MAX8647)
An I 2 C 2-wire serial interface is provided on the MAX8647 to control the LEDs. The serial interface consists of a serial-data line (SDA) and a serial-clock line (SCL). Standard I 2 C write-byte commands are
8
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Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN MAX8647/MAX8648
C3 1F C2 1F
VIN 2.7V TO 5.5V C1 1F
C1P IN
C1N C2P INVERTING CHARGE PUMP
C2N NEG
TP7
GND SEL MIN 1MHz OSCILATOR
EP
C4 1F
CURRENT REGULATOR LED1 VDD (ENA) SCL (ENB) SDA (ENC) I2C OR SERIAL PULSE INTERFACE AND CONTROL CURRENT SOURCE CONTROL BIAS
VIN
CURRENT REGULATOR THERMAL SHUTDOWN CURRENT REGULATOR
LED2
LED3
CURRENT REGULATOR
LED4
MAX8647 MAX8648
CURRENT REGULATOR LED5
( ) ARE FOR THE MAX8648
CURRENT REGULATOR
LED6
Figure 1. Block Diagram and Application Circuit
Shutdown Mode
The MAX8647 is shutdown when all LEDs are turned off through the I2C port. In shutdown, the I2C port is still active and ready to receive a command.
The MAX8648 is shutdown when all three EN_ are held low for 4ms or longer. In shutdown, NEG is pulled to GND with a 10k internal resistor.
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Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN MAX8647/MAX8648
Table 2. I2C Control Data Byte--Device Address 0x9A
SDA CONTROL BYTE FUNCTION Not used LED1 current LED2 current LED3 current LED4 current LED5 current LED6 current Not used COMMAND C2 0 0 0 0 1 1 1 1 C1 0 0 1 1 0 0 1 1 C0 0 1 0 1 0 1 0 1 D4 -- D3 -- DATA D2 -- D1 -- D0 --
24.0mA to 0.1mA and off in 32 steps 24.0mA to 0.1mA and off in 32 steps 24.0mA to 0.1mA and off in 32 steps 24.0mA to 0.1mA and off in 32 steps 24.0mA to 0.1mA and off in 32 steps 24.0mA to 0.1mA and off in 32 steps -- -- -- -- --
Note: C2 is MSB and D0 is LSB. The power-on default settings for D4 to D0 are all 0, which indicates that all LED_ are off.
Table 3. MAX8647 I2C Data vs. LED Currents
D4 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 D3 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 D2 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 D1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 D0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 mA 24 22.4 20.8 19.2 17.6 16 14.4 12.8 11.2 9.6 8 6.4 5.6 4.8 4 3.2 D4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D3 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 D2 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 D1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 D0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 mA 2.8 2.4 2 1.6 1.4 1.2 1 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 OFF
Temperature Derating Function
The MAX8647/MAX8648 contain a derating function that automatically limits the LED current at high temperatures to help protect the LEDs from damage. The derating function enables the safe usage of higher LED current at room temperature, thus reducing the number of LEDs required to backlight the display. The derating circuit lowers the LED current at approximately 2.5%/C once the IC is above +60C. The typical derating function characteristic is shown in the Typical Operating Characteristics.
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Power-Up LED Detection and Fault Protection
The MAX8648 contains special circuitry to detect shortcircuit conditions at power-up and disable the corresponding current regulator to avoid wasting battery current. Connect any unused LED_ to IN to disable the corresponding current regulator. If an LED fails short circuit, the current regulator continues the current regulated operation until power to the IC is cycled and the short circuit is detected. An open-circuit LED failure drives the voltage on the corresponding LED_ output
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Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN MAX8647/MAX8648
A tLOW B tHIGH C D E F G H I J K L M
SCL
SDA
tSU_STA
tHD_STA
tSU_DAT
tHD_DAT F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO SLAVE (OP/SUS BIT) H = LSB OF DATA CLOCKED INTO SLAVE I = SLAVE PULLS SMBDATA LINE LOW
tSU_STO J = ACKNOWLEDGE CLOCKED INTO MASTER K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION, DATA EXECUTED BY SLAVE M = NEW START CONDITION
tBUF
A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE E = SLAVE PULLS SMBDATA LINE LOW
Figure 2. Definition of Timing for I2C Bus
Table 4. MAX8648 Pulse Dimming Step vs. LED Currents
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 MAX8648 DIMMING STEPS Startup or EN_ high 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 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 24.0 MAX8648 DIMMING STEPS 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
below the switch over threshold enabling the inverting charge pump. For the MAX8647, program any unused LED_ to off using the I2C interface. Unused LED_ can be connected to IN or left unconnected.
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. Adding a lowpass filter to the input of the MAX8647/MAX8648 further reduces input ripple. Alternatively, increasing CIN to 2.2F (or 4.7F) cuts input ripple in half (or in fourth) with only a small increase in footprint.
11
Thermal Shutdown
The MAX8647/MAX8648 includes a thermal-limit circuit that shuts down the IC above about +160C. The IC turns on after it cools by approximately 20C.
______________________________________________________________________________________
Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN MAX8647/MAX8648
0 EN_ INITIAL tHI > 120s 24mA ILED_ 0mA tLO 1s TO 500s 17.6 16.0 0.6 0.5 0.4 0.3 0.2 tHI > 1s 24mA 22.4 tSHDN 4ms 1 2 3 4 5 26 27 28 29 30 31
22.4
20.8
19.2
0.1mA
0mA
Figure 3. EN_ Timing Diagram
Capacitor 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).
Driving LEDs with Multiple Supplies
It is not necessary for the LED anodes to connect to IN. Figure 7 shows an example using separate supplies to power the LED_ groups of the MAX8648. In this example, the voltage source (V1) provides power for RGB LEDs (LED1, LED2, and LED3). V2 provides power for backlight LEDs (LED4 and LED5), and V3 provides power for a red charge indicator (LED6).
PCB Layout and Routing
The MAX8647/MAX8648 have a high-frequency, switched-capacitor voltage inverter. For best circuit performance, use a solid copper plane and place C1-C4 as close as possible to the MAX8647/MAX8648. Figure 4 shows the MAX8648 evaluation kit example layout.
Figure 4. MAX8648 Evaluation Kit Layout for C1-C4
Chip Information
PROCESS: BiCMOS
12
______________________________________________________________________________________
Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN MAX8647/MAX8648
1F 1F
1F
1F
C1P INPUT 2.7V TO 5.5V 1F GND
C1N
C2P
C2N NEG
C1P
1F
C1N
C2P
C2N NEG
1F
INPUT 2.7V TO 5.5V 1F
IN EP WHITE OR RGB LED
IN EP GND WHITE OR RGB LED
MAX8647
I2C PORT ON/OFF AND BRIGHTNESS SDA SCL
LED1 LED2 LED3 LED4
D1 D2 D3 D4 D5 D6
MAX8648
LED1 LED2
D1 D2 D3 D4 D5 D6
ENA SERIALPULSE INTERFACE ENB ENC
LED3 LED4 LED5 LED6
VLOGIC 1.7V TO 5.5V 0.1F
VDD
LED5 LED6
Figure 5. MAX8647 Typical Application Circuit
Figure 6. MAX8648 Typical Application Circuit
1F
1F
C1P INPUT 2.7V TO 5.5V 1F GND
C1N
C2P
C2N NEG
1F
IN EP WHITE OR RGB LED V1 V2 V3
MAX8648
LED1 LED2
D1 RGB BACKLIGHT D2 D3 D4 D5 D6 RED CHARGE INDICATOR
ENA SERIALPULSE INTERFACE ENB ENC
LED3 LED4 LED5 LED6
Figure 7. Driving LEDs with Multiple Supplies
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13
Ultra-Efficient Charge Pumps for Six White/RGB LEDs in 3mm x 3mm Thin QFN MAX8647/MAX8648
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 Charge Pumps for Six White/RGB LEDs 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.)
MAX8647/MAX8648
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 0.55 12 3 3 0.02 0.20 REF 0.25 0.05 0 0.80 0.30 3.10 3.10 0.65
16L 3x3 MIN. NOM. MAX. 0.70 0.20 2.90 2.90 0.30 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.
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
SPRINGER
is a registered trademark of Maxim Integrated Products, Inc.

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