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4 White LED Backlight Driver ADM8843
FEATURES
Drives 4 LEDs from a 2.6 V to 5.5 V (Li-Ion) input supply 1x/1.5x/2x fractional charge pump to maximize power efficiency 0.3% typical LED current matching Up to 88% power efficiency over Li-Ion range Powers main and sub display LEDs with individual shutdown Package footprint only 9 mm2 (3 mm x 3 mm) Package height only 0.9 mm Low power shutdown mode Shutdown function Soft-start limiting in-rush current
GENERAL DESCRIPTION
The ADM8843 uses charge pump technology to provide the power to drive up to four LEDs. The LEDs are used for backlighting a color LCD display, having regulated constant current for uniform brightness intensity. The main display can use up to three LEDs, and the sub display uses one LED. The CTRL1 and CTRL2 digital input control pins control the shutdown operation and the brightness of the main and sub displays. To maximize power efficiency, the charge pump can operate in either 1x, 1.5x, or 2x mode. The charge pump automatically switches between 1x/1.5x/2x modes, based on the input voltage, to maintain sufficient drive for the LED anodes at the highest power efficiency. Improved brightness matching of the LEDs is achieved by a feedback pin that senses individual LED current with a typical matching accuracy of 0.3%.
APPLICATIONS
Cellular phones with main and sub displays White LED backlighting Camera flash/strobes and movie light applications Micro TFT color displays DSC PDAs
FUNCTIONAL BLOCK DIAGRAM
C1 1F C2 1F
VCC C4 4.7F
ADM8843
CHARGE PUMP 1x/1.5x/2x MODE
VOUT C3 2.2F
MAIN
SUB
OSC CTRL1 CTRL2 CONTROL LOGIC
VREF FB1 FB2 FB3 FB4
CURRENT CONTROL 1
CURRENT CONTROL 2
CURRENT CONTROL 3
ISET RSET
LED CURRENT CONTROL CIRCUIT
GND
Figure 1. Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 (c) 2004 Analog Devices, Inc. All rights reserved.
05050-001
CURRENT CONTROLLED SINKS
CURRENT CONTROL 4
ADM8843 TABLE OF CONTENTS
Specifications......................................................................................3 Absolute Maximum Ratings.............................................................4 Thermal Characteristics .............................................................. 4 ESD Caution.................................................................................. 4 Pin Configuration and Function Descriptions..............................5 Typical Performance Characteristics ..............................................6 Theory of Operation .........................................................................9 Automatic Gain Control............................................................ 10 Brightness Control with a Digital PWM Signal ..................... 10 LED Brightness Control Using a PWM Signal Applied to VPWM ............................................................................................. 12 LED Brightness Control Using a DC Voltage Applied to VBRIGHT .......................................................................................... 12 Applications......................................................................................13 Layout Considerations and Noise ............................................ 13 White LED Shorting .................................................................. 13 Driving Four LEDs in the Main Display Only ....................... 13 Driving Fewer than Four LEDs ................................................ 13 Using Smaller Capacitor Values ............................................... 14 Power Efficiency......................................................................... 15 Outline Dimensions ........................................................................16 Ordering Guide .......................................................................... 16
REVISION HISTORY
10/04--Revision 0: Initial Version
Rev. 0 | Page 2 of 16
ADM8843 SPECIFICATIONS
VCC = 2.6 V to 5.5 V; TA = -40C to +85C, unless otherwise noted; C1, C2 = 1.0 F; C3 = 2.2 F; C4 = 4.7 F
Table 1.
PARAMETER INPUT VOLTAGE, VCC SUPPLY CURRENT, ICC SHUTDOWN CURRENT CHARGE PUMP FREQUENCY CHARGE PUMP MODE THRESHOLDS 1.5x to 2x 2x to 1.5x Hysteresis 1x to 1.5x 1.5x to 1x Hysteresis ISET PIN LED : LED Matching ISET Pin Voltage ILED to ISET Ratio ILED to ISET Ratio Accuracy MIN COMPLIANCE ON FBx PIN CHARGE PUMP OUTPUT RESISTANCE Min 2.6 Typ 2.6 Max 5.5 5 5 1.5 3.33 3.36 40 4.77 4.81 40 0.3 1.18 120 5% 0.15 1.2 3.5 8.0 0.1 0.7 VCC 0.3 VCC 1 88 30 20 200 Unit V mA A MHz V V mV V V mV % V ILED = 20 mA, VFB = 0.4 V Test Conditions All four LEDs disabled, VCC = 3.3 V, RSET = 7.08 k, CTRL1 = 1, CRTL2 = 1
LED CURRENT PWM DIGITAL INPUTS Input High Input Low Input Leakage Current CHARGE PUMP POWER EFFICIENCY VOUT RIPPLE ______________________
1
V mA kHz V V A % mV
ISET = 15 mA 1x mode 1.5x mode 2x mode Note 1
CTRL1 = 1, CRTL2 = 1, VCC = 3.4V, VFB = 0.2 V, IFB = 20 mA VCC = 3.6 V, ILED = 20 mA, all four LEDs enabled
Guaranteed by design. Not 100% production tested.
Rev. 0 | Page 3 of 16
ADM8843 ABSOLUTE MAXIMUM RATINGS
TA = 25C, unless otherwise noted. Table 2.
Parameter Supply Voltage VCC ISET CTRL1, CTRL2 VOUT Shorted1 Feedback Pins FB1 to FB4 Operating Temperature Range VOUT2 Storage Temperature Range Power Dissipation ESD Class ___________________________
1 2
Rating -0.3 V to +6.0 V -0.3 V to +2.0 V -0.3 V to +6.0 V Indefinite -0.3 V to +6.0 V -40C to +85C 180 mA -65C to +125C 2 mW 1
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
THERMAL CHARACTERISTICS
16-Lead LFCSP Package: JA = 50C/W
Short through LED. Based on long-term current density limitations.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
Rev. 0 | Page 4 of 16
ADM8843 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
16 C1+ 15 VCC 13 CTRL1 14 C1-
VOUT 1 C2+ 2 ISET 3 GND 4
PIN 1 INDICATOR
12 CTRL2 11 C2- 10 GND 9 GND
ADM8843
TOP VIEW (Not to Scale)
FB1 5
FB2 6
FB3 7
FB4 8
Figure 2. Pin Configuration
Table 3. Pin Function Descriptions
Pin No. 1 2 3 4, 9, 10 5-8 Mnemonic VOUT C2+ ISET GND FB1-FB4 Description Charge Pump Output. A 2.2 F capacitor to ground is required on this pin. Connect VOUT to the anodes of all the LEDs. Flying Capacitor 2 Positive Connection. Bias Current Set Input. The current flowing through the RSET resistor, ISET, is gained up by 120 to give the ILED current. Connect a resistor RSET to GND to set the bias current as VSET/RSET. Note that VSET = 1.18 V. Device Ground Pins. LED1-LED4 Cathode Connection and Charge Pump Feedback. The current flowing in these LEDs is 120 times the current flowing through RSET, ISET. When using fewer than four LEDs, this pin can be left unconnected or connected to GND. Flying Capacitor 2 Negative Connection. Digital Input. 3 V CMOS Logic. Used with CTRL1 to control the shutdown operation of the main and sub LEDs. Digital Input. 3 V CMOS Logic. Used with CTRL2 to control the shutdown operation of the main and sub LEDs. Flying Capacitor 1 Negative Connection. Positive Supply Voltage Input. Connect this pin to a 2.6 V to 5.5 V supply with a 4.7 F decoupling capacitor. Flying Capacitor 1 Positive Connection. Expose Paddle. Connect the exposed paddle to GND.
11 12 13 14 15 16 -
C2- CTRL2 CTRL1 C1- VCC C1+ EP
Rev. 0 | Page 5 of 16
05050-003
ADM8843 TYPICAL PERFORMANCE CHARACTERISTICS
35 20.35 20.30 -40C 20.25 20.20 +25C 20.15 +85C 20.10 20.05
05050-004
30
LED CURRENT (mA)
25
20
15
10
6.75
10.75 8.75 RSET (k)
12.75
14.75
3.1
4.1 3.6 4.6 SUPPLY VOLTAGE (k)
5.1
5.6
Figure 3. ILED (mA) vs. RSET
20.24 20.22
Figure 6. ILED (mA) vs. Temperature (C), Four LEDs Enabled
35
30
20.20
LED CURRENT (mA)
LED CURRENT (mA)
20.18 20.16 20.14 20.12 20.10 20.08 -40
05050-005
25
20
15
10
0
40 TEMPERATURE (C)
80
3.0
3.4
3.8 4.2 4.6 SUPPLY VOLTAGE (V)
5.0
5.4
Figure 4. ILED (mA) Variation over Temperature (C), VCC = 3.6 V
Figure 7. ILED (mA) vs. Supply Voltage (V)
95
20
90
16
LED CURRENT (mA)
85
12
EFFICIENCY (%)
80 75 70
8
4
65
05050-006
0 0 20 40 60 DUTY CYCLE (%) 80 100
0
10
20
30
40 50 60 DUTY CYCLE (%)
70
80
90
100
Figure 5. ILED (mA) vs. PWM Dimming (Varying Duty Cycle), Four LEDs Enabled, Frequency = 1 kHz
Figure 8. LED Efficiency vs. Varying Duty Cycle of 1 kHz PWM Signal, Four LEDs Enabled, 20 mA/LED
Rev. 0 | Page 6 of 16
05050-009
60
05050-008
5 2.6
05050-007
5 4.75
LED CURRENT (mA)
20.00 2.6
ADM8843
180 -40C 160
CTRL1/2
+25C +85C
1
SUPPLY CURRENT (mA)
140
120
CURRENT
2
100
80
VOUT
5050-013
05050-010
60 2.6
3
3.0
3.4
3.8 4.2 4.6 SUPPLY VOLTAGE (V)
5.0
5.4
CH1 2.00V CH3 1.00V
B
W
CH2 160mA
B
W
M 10.0s CH2
-2.44mV
Figure 9. Supply Current vs. Supply Voltage over Temperature, Four LEDs Enabled @ 20 mA/LED
Figure 12. Soft Start Showing the Initial In-Rush Current and VOUT Variation, Four LEDs @ 20 mA/LED, VCC = 3.6 V
VCC
2
VCC
1
VOUT
1
VOUT
05050-011
2
05050-014
CH1 20.0mV
B
W
CH2 20.0mV
B
W
M 10.0s CH1
-12.8mV
CH1 20.0mV
B
W
CH2 20.0mV
B
W
M 400ns
CH2
2.4mV
Figure 10. 1.5x Mode Operating Waveforms
Figure 13. 2x Mode Operating Waveforms
90 85 80
POWER EFFICIENCY
VF = 3.6V VF = 4.0V VF = 4.3V
75 70 65 60 55 50 VF = 3.8V VF = 3.2V
VCC
1
VOUT
2
5050-012
45
5050-015
CH1 20.0mV
B
W
CH2 20.0mV
B
W
M 400ns CH2
2.4mV
40 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 VCC
Figure 11. 1x Mode Operating Waveforms
Figure 14. Power Efficiency vs. Supply Voltage over Li-Ion Range, Four LEDs @ 20 mA/LED
Rev. 0 | Page 7 of 16
ADM8843
90 85 80
POWER EFFICIENCY
VF = 3.8V VF = 4.0V VF = 4.3V
1
CTRL1/2
C2 FALL : 44.0ms @: -44.4ms 200s LOW SIGNAL AMPLITUDE
75 70 65 60 55 VF = 3.6V 50 45
VOUT
05050-016
40 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 VCC
CH1 2.00V
CH2 2.00mV
M 10.0ms CH2
4.36mV
Figure 16. TPC Delay Figure 15. Power Efficiency vs. Supply Voltage over Li-Ion Range, Four LEDs @ 15 mA/LED
Rev. 0 | Page 8 of 16
05050-017
VF = 3.2V
2
ADM8843 THEORY OF OPERATION
The ADM8843 charge pump driver for LCD white LED backlights implements a multiple-gain charge pump (1x, 1.5x, 2x) to maintain the correct voltage on the anodes of the LEDs over a 2.6 V to 5.5 V (Li-Ion) input supply voltage. The charge pump automatically switches between 1x/1.5x/2x modes, based on the input voltage, to maintain sufficient drive for the LED anodes, with VCC input voltages as low as 2.6 V. It also includes regulation of the charge pump output voltage for supply voltages up to 5.5 V. The ADM8843's four LEDs are arranged into two groups, main and sub. The main display can have up to three LEDs (FB1 to FB3), and the sub display has one LED (FB4) (see Figure 18). The CTRL1 and CTRL2 digital input control pins control the shutdown operation and the brightness of the main and sub displays (see Table 4). Table 4. Shutdown Truth Table
CTRL1 0 0 1 1 CTRL2 0 1 0 1 LED Shutdown Operation Sub Display Off / Main Display Off Sub Display Off / Main Display On Sub Display On / Main Display Off Sub Display On / Main Display On
An external resistor, RSET, is connected between the ISET pin and GND. This resistor sets up a reference current, ISET, which is internally gained up by 120 within the ADM8843 to produce ILED currents of up to 20 mA/LED (ILED = ISET x 120 and ISET = 1.18 V/RSET). The ADM8843 uses four individual current sinks to individually sense each LED current with a typical matching performance of 0.3%. This current matching performance ensures uniform brightness across a color display. The ADM8843 lets the user control the brightness of the white LEDs with a digital PWM signal applied to CTRL1 and/or CTRL2. The duty cycle of the applied PWM signal determines the brightness of the main and/or sub display backlight white LEDs. The ADM8843 also allows the brightness of the white LEDs to be controlled using a dc voltage (see Figure 17). Softstart circuitry limits the in-rush current flow at power-up. The ADM8843 is fabricated using CMOS technology for minimal power consumption, and is packaged in a 16-lead lead frame chip scale package.
ADM8843
ISET VBRIGHT 0V-2.5V R = 15k RSET = 13.4k
05050-022
Figure 17. PWM Brightness Control Using a DC Voltage Applied to VBRIGHT
C1 1F
C2 1F
VCC C4 4.7F
ADM8843
CHARGE PUMP 1x/1.5x/2x MODE
VOUT C3 2.2F
MAIN
SUB
OSC CTRL1 CTRL2 CONTROL LOGIC
VREF FB1 FB2 FB3 FB4
CURRENT CONTROL 1
CURRENT CONTROL 2
CURRENT CONTROL 3
ISET RSET
LED CURRENT CONTROL CIRCUIT
GND
Figure 18. Functional Block Diagram
Rev. 0 | Page 9 of 16
05050-001
CURRENT CONTROLLED SINKS
CURRENT CONTROL 4
ADM8843
AUTOMATIC GAIN CONTROL
The automatic gain control block controls the operation of the charge pump by selecting the appropriate gain for the charge pump. Doing so maintains sufficient drive for the LED anodes at the highest power efficiency over a 2.6 V to 5.5 V input supply range. The charge pump switching thresholds are described in Table 5. Table 5. Charge Pump Switching Thresholds
Gain 1.5x to 2x 2x to 1.5x 1x to 1.5x 1.5x to 1x Threshold 3.33 V 3.36 V 4.77 V 4.81 V
By applying a digital PWM signal to the digital input control pins, CTRL1 and/or CTRL2 adjust the brightness of the sub and/or main displays. The ADM8843's four white LEDs are organized into two groups, main display (FB1 to FB3) and sub display (FB4); refer to the Theory of Operation section. The ADM8843's main and sub display brightness can be controlled together or separately. It does this by applying a digital PWM signal to both the CTRL1 and CTRL2 pins. The duty cycle of the applied digital PWM signal determines the brightness of the main and sub displays together. Varying the duty cycle of the applied PWM signal varies the brightness of the main and sub displays from 0% to 100%. By holding CTRL1 low and applying a digital PWM signal to CTRL2, the sub display is turned off and the main display is turned on. Then the brightness of the main display is determined by the duty cycle of the applied digital PWM signal. By applying a digital PWM signal to CTRL1 and holding CTRL2 low, the sub display is turned on and the main display is turned off. Then the brightness of the sub display is determined by the duty cycle of the applied digital PWM signal. By applying a digital PWM signal to CTRL1 and holding CTRL2 high, the sub display is turned on and the main display is turned on. Then the brightness of the sub display is determined by the duty cycle of the applied digital PWM signal. The brightness of the main display is set to the maximum (maximum is set by RSET). By holding CTRL1 high and applying a digital PWM signal to CTRL2, the sub display is turned on and the main display is turned on. Then the brightness of the main display is determined by the duty cycle of the applied digital PWM signal. The brightness of the sub display is set to the maximum (maximum is set by RSET). When CTRL1 and CTRL2 are low, the LED current control sinks shutdown. Shutdown of the charge pump is delayed by 15 ms. This timeout period, tCP, allows the ADM8843 to determine if a digital PWM signal is present on CTRL1 and CTRL2, or if the user has selected a full chip shutdown (see Figure 20). If digital PWM brightness control of the LEDs is not required, a constant Logic Level 1 (VCC) or 0 (GND) must be applied. The four white LED in the ADM8843 are arranged into two groups, sub and main. It is possible to configure the four LEDs as in Table 6. Refer also to Figure 20.
05050-018
BRIGHTNESS CONTROL WITH A DIGITAL PWM SIGNAL
PWM brightness control provides the widest brightness control method by pulsing the white LEDs on and off using the digital input control pins, CTRL1 and/or CTRL2. PWM brightness control also removes any chromaticity shifts associated with changing the white LED current, because the LEDs operate at either zero current or full current (set by RSET). The digital PWM signal applied with a frequency of 100 Hz to 200 kHz turns the current control sinks on and off using CTRL1 and/or CTRL2. The average current through the LEDs changes with the PWM signal duty cycle. If the PWM frequency is much less than 100 Hz, flicker could be seen in the LEDs. For the ADM8843, zero duty cycle turns off the LEDs, and a 50% duty cycle results in an average LED current ILED being half the programmed LED current. For example, if RSET is set to program 20 mA/LED, a 50% duty cycle results in an average ILED of 10 mA/LED, ILED being half the programmed LED current.
C1 1F 3.4V I IN VCC C2 1F
VOUT
ADM8845
PWM INPUT OR HIGH/LOW PWM INPUT OR HIGH/LOW CTRL1 FB1 FB2 FB3 FB4
C3 2.2F
CTRL2
ISET RSET
Figure 19. Digital PWM Brightness Control Application Diagram
Rev. 0 | Page 10 of 16
ADM8843
Table 6. Digital Inputs Truth Table
CTRL1 0 0 1 1 0 PWM 1 PWM PWM CTRL2 0 1 0 1 PWM 0 PWM 1 PWM LED Operation Sub Display Off / Main Display Off (Full Shutdown)1, 2 Sub Display Off / Main Display On1, 3 Sub Display On / Main Display Off1, 2 Sub Display On / Main Display On (Full On) 1, 3 Sub Display Off/ Digital PWM Brightness Control on Main Display4, 5 Digital PWM Brightness Control on Sub Display / Main Display Off2, 4 Sub Display On/ Digital PWM Brightness Control on Main Display1, 5 Digital PWM Brightness Control on Sub Display / Main Display On5 Digital PWM Brightness Control on Sub and Main Display
5
1 2 3
Sub display on means the display is on with the maximum brightness set by the RSET resistor. CTRL1 = 1 means a constant logic level (VCC) is applied to CTRL1. Main display off means the main display only is off. CTRL2 = 0 means a constant logic level (GND) is applied to CTRL2. Main display on means the display is on with the maximum brightness set by the RSET resistor. CTRL2 = 1 means a constant logic level (VCC) is applied to CTRL2. 4 Sub display off means the sub display LEDs only is off. CTRL1 = 0 means a constant logic level (GND) is applied to CTRL1. 5 PWM means a digital PWM signal is applied to the CTRL1 and/or the CTRL2 pin with a frequency from 100 Hz to 200 kHz.
LED CONFIG.
FULL ON
SUB AND MAIN 50% DUTY CYCLE
MAIN AND SUB OFF
MAIN 80% DUTY CYCLE, SUB OFF
tCP
CTRL1
CTRL2
VOUT ILED (SUB) ILED (MAIN) 100% SUB DISPLAY BRIGHTNESS 50% SHDN 80%
100% MAIN DISPLAY BRIGHTNESS 50%
SHDN
05050-020
37ms > tCP > 15ms
Figure 20. Application Timing
Rev. 0 | Page 11 of 16
ADM8843
LED BRIGHTNESS CONTROL USING A PWM SIGNAL APPLIED TO VPWM
Adding two external resistors and a capacitor, as shown in Figure 21, can also be used for PWM brightness control. This PWM brightness control method can be used instead of CTRL1 and/or CTRL2 digital PWM brightness control. With this configuration, CTRL1 and CTRL2 digital logic pins can control shutdown of the white LEDs, while VPWM can control the brightness of all the white LEDs. This is done by applying a high frequency PWM signal (amplitude 0 V to 2.5 V) to drive an R-C-R filter on the ISET pin of the ADM8843. A 0% PWM duty cycle corresponds to 20 mA/LED, while a 100% PWM duty cycle corresponds to a 0 mA/LED. At PWM frequencies above 5 kHz, C5 may be reduced (see Figure 21). The amplitude of the PWM signal must be 0 V and 2.5 V only in order to have 20 mA flowing in each LED.
I LED (1 - Duty Cycle) I _ Voltage = SET x 120 x RSET x 2R 100 RSET + 2R
LED BRIGHTNESS CONTROL USING A DC VOLTAGE APPLIED TO VBRIGHT
By adding one resistor, as shown in Figure 17, this configuration can also be used for brightness control of the white LEDs by using a dc voltage applied to the VBRIGHT node. Figure 22 shows an application example of LED brightness control using a dc voltage with a amplitude of 0 V to 2.5 V applied to VBRIGHT. The equation for ILED is ISET = [(1/RSET + 1/R)(VSET)] - [(1/R)(VBRIGHT)] ILED = 120 x ISET where: R = 15 k VSET = voltage at ISET pin (1.18 V)
2.5V VBRIGHT 1.6V 0.8V 0V
20mA 13.6mA 100% = ILED = 0mA 0% = ILED = 20mA
05050-023
ADM8843
ISET
ILED 0mA
7.2mA
C5 = 1F
RSET = 13.4k
Figure 21. PWM Brightness Control Using Filter -PWM Signal
05050-021
VPWM 0V-2.5V
R = 7.5k R = 7.5k
Figure 22. PWM Brightness Control Application Diagram Using a DC Voltage Applied to VBRIGHT
Rev. 0 | Page 12 of 16
ADM8843 APPLICATIONS
LAYOUT CONSIDERATIONS AND NOISE
Because of the ADM8843's switching behavior, PCB trace layout is an important consideration. To ensure optimum performance, a ground plane should be used, and all capacitors (C1, C2, C3, C4) must be located with minimal track lengths to the pins of the ADM8843.
DRIVING FOUR LEDS IN THE MAIN DISPLAY ONLY
The ADM8843 can be operated with four LEDs in the main display only (see Figure 23). With this configuration, CTRL1 and CTRL2 are used together to control the main display shutdown operation and brightness control.
DRIVING FEWER THAN FOUR LEDS
The ADM8843 can be operated with fewer than four LEDs in parallel by simply leaving the unused FBx pins floating or by connecting them to GND. For example, Figure 24 shows three LEDs being powered by the ADM8843.
WHITE LED SHORTING
If an LED is shorted, the ADM8843 continues to drive the remaining LEDs with ILED per LED (ILED = ISET x 120 mA). This is because the ADM8843 uses four internal currents sinks to produce the LED current. If an LED is shorted, the ADM8843 continues to sink (ISET x 120
LCD
MAIN DISPLAY
VCC 2.6V-5.5V VOUT
VCC 2.6V-5.5V VOUT
ADM8843
CTRL1 CTRL2 FB1 FB2 FB3 FB4 ISET RSET GND
05050-024
ADM8843
CTRL1 CTRL2 FB1 FB2 FB3 FB4 ISET RSET GND
05050-025
Figure 23. Driving Four White LEDs
MAIN DISPLAY
Figure 24. Driving Three White LEDs
SUB DISPLAY
VCC 2.6V-5.5V VOUT
ADM8843
CTRL1 CTRL2 FB1 FB2 FB3 FB4 GND
05050-002
ISET RSET
Figure 25. Typical Application Diagram
Rev. 0 | Page 13 of 16
ADM8843
USING SMALLER CAPACITOR VALUES
The ADM8843 can be operated with the smaller capacitor values described here to reduce capacitor footprint sizes. Option 1 Input and output ripple plots for 1x and 1.5x mode operation are shown with C1,C2 = 0.22 F; C3 = 0.47 F and C4 = 1 F. Option 2 Input and output ripple plots for 1x and 1.5x mode operation are shown with C1,C2 = 0.22 F; C3 = 0.47 F and C4 = 4.7 F.
VCC
2
VCC
2
VOUT
3
05050-026
VOUT
3
05050-028
CH2 10.0mV CH3 10.0mV
B W
B
W
M 400ns CH3
-33mV
CH2 10.0mV CH3 10.0mV
B W
B
W
M 1.00s CH3
-33mV
Figure 26. 1x Mode Operation with Four LEDs with 20 mA/LED at VCC = 5.0 V, with a 1 F VCC Decoupling Capacitor
Figure 28. 1x Mode Operation with Four LEDs with 20 mA/LED at VCC = 5.0 V, with a 4.7 F VCC Decoupling Capacitor
VCC
2
VCC
2
VOUT
3
05050-027
VOUT
3
CH2 20.0mV CH3 50.0mV
B W
B
W
M 400ns CH3
-33mV
CH3 50.0mV
B W
CH2 20.0mV
B
W
M 400ns CH3
-33mV
Figure 27. 1.5x Mode Operation with Four LEDs with 20 mA/LED at VCC = 3.6 V, with a 1 F VCC Decoupling Capacitor
Figure 29. 1.5x Mode Operation with Four LEDs with 20 mA/LED at VCC = 3.6 V, with a 4.7 F VCC Decoupling Capacitor
Rev. 0 | Page 14 of 16
05050-029
ADM8843
POWER EFFICIENCY
The ADM8843 power efficiency () equations are as follows: = POUT/PIN PIN = ((VCC x ILOAD x Gain) + (IQ x VCC)) POUT = 4 x (VF x ILED) where: IQ is the quiescent current of the ADM8843, 2.6 mA. VF is the LED forward voltage. Gain is the charge pump mode (1x, 1.5x, 2x). Example 1 The ADM8843 driving four white LED with 20 mA/LED at VCC = 3.4 V (1.5x mode), LED VF = 4.5 V. PIN = ((VCC x ILOAD x Gain) + (VCC x IQ)) PIN = ((3.4 x 80 mA x 1.5) + (3.4 x 2.6 mA)) PIN = ((0.408) + (0.00884)) PIN = 0.41684 POUT = 4(VF x ILED) POUT = 4(4.5 V x 20 mA) POUT = 0.36 = POUT/PIN = 0.36/0.41684 = 87 %
VCC = 3.4V IIN VCC VOUT
Example 2 The ADM8843 driving four white LED with 20 mA/LED at VCC = 3.4 (1.5x mode), LED VF = 3.6 V. PIN = ((VCC x ILOAD x Gain) + (VCC x IQ)) PIN = ((3.4 x 80 mA x 1.5) + (3.4 x 2.6 mA)) PIN = ((0.408) + (0.00884)) PIN = 0.41684 POUT = 4(VF x ILED) POUT = 4(3.6 V x 20 mA) POUT = 0.288 = POUT/PIN = 0.288/0.41684 = 70 %
ILOAD
ADM8843
CTRL1 CTRL2 FB1 FB2 FB3 FB4 GND
05050-019
RSET 7.32k
ISET
Figure 30. Charge Pump Power Efficiency Diagram, Example 1
Rev. 0 | Page 15 of 16
ADM8843 OUTLINE DIMENSIONS
0.50 0.40 0.30 PIN 1 INDICATOR
16 1
3.00 BSC SQ 0.45 PIN 1 INDICATOR TOP VIEW 2.75 BSC SQ 0.50 BSC 12 MAX 1.00 0.85 0.80 SEATING PLANE 0.30 0.23 0.18 0.80 MAX 0.65 TYP 0.05 MAX 0.02 NOM 0.20 REF
0.60 MAX
13 12
1.65 1.50 SQ* 1.35
EXPOSED PAD
9 (BOTTOM VIEW) 4 8 5
0.25 MIN
1.50 REF
*COMPLIANT TO JEDEC STANDARDS MO-220-VEED-2 EXCEPT FOR EXPOSED PAD DIMENSION
Figure 31. 16-Lead Lead Frame Chip Scale Package [LFCSP] 3 mm x 3 mm Body (CP-16-3) Dimensions shown in millimeters
ORDERING GUIDE
Model ADM8843ACPZ-REEL71 Temperature Range -40C to + 85C Package Description 16-Lead Lead Frame Chip Scale Package Package Option CP-16-3 Branding M2U
1
Z = Pb-free part.
(c) 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05050-0-10/04(0)
Rev. 0 | Page 16 of 16
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