Four White LED Backlight Driver ADM8843 FEATURES GENERAL DESCRIPTION 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 0.55 mm Low power shutdown mode Shutdown function Soft start limiting in-rush current 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 that has 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 1x, 1.5x, or 2x mode. The charge pump automatically switches among 1x/1.5x/2x modes, based on the input voltage, to maintain sufficient drive for the LED anodes at the highest power efficiency. APPLICATIONS Cellular phones with main and sub displays White LED backlighting Camera flash/strobes and movie light applications Micro TFT color displays DSC PDAs 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%. FUNCTIONAL BLOCK DIAGRAM C1 1F VCC C2 1F ADM8843 VOUT CHARGE PUMP 1x/1.5x/2x MODE C4 4.7F C3 2.2F MAIN SUB OSC CTRL1 CTRL2 CONTROL LOGIC VREF CURRENT CONTROLLED SINKS GND 05050-001 CURRENT CONTROL 4 CURRENT CONTROL 3 RSET LED CURRENT CONTROL CIRCUIT CURRENT CONTROL 2 ISET CURRENT CONTROL 1 FB1 FB2 FB3 FB4 Figure 1. Rev. C 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: 781.461.3113 (c)2004-201 Analog Devices, Inc. All rights reserved. ADM8843 TABLE OF CONTENTS Features .............................................................................................. 1 Brightness Control with a Digital PWM Signal ..................... 10 Applications....................................................................................... 1 LED Brightness Control Using a PWM Signal Applied to VPWM .................................... 12 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 LED Brightness Control Using a DC Voltage Applied to VBRIGHT ................................... 12 Revision History ............................................................................... 2 Applications..................................................................................... 13 Specifications..................................................................................... 3 Layout Considerations and Noise ............................................ 13 Absolute Maximum Ratings............................................................ 4 White LED Shorting .................................................................. 13 Thermal Characteristics .............................................................. 4 Driving Four LEDs in the Main Display Only ....................... 13 ESD Caution.................................................................................. 4 Driving Fewer than Four LEDs ................................................ 13 Pin Configuration and Function Descriptions............................. 5 Using Smaller Capacitor Values ............................................... 14 Typical Performance Characteristics ............................................. 6 Power Efficiency......................................................................... 15 Theory of Operation ........................................................................ 9 Outline Dimensions ....................................................................... 16 Automatic Gain Control............................................................ 10 Ordering Guide .......................................................................... 16 REVISION HISTORY 1/11--Rev. B to Rev. C Changes to Figure 14........................................................................ 7 4/10--Rev. A to Rev. B Removed CP-16-12 Package .............................................Universal Change to Figure 2 ........................................................................... 5 Change to Figure 6 ........................................................................... 6 Changes to Figure 14........................................................................ 7 Changes to Figure 15........................................................................ 8 Updated Outline Dimensions ....................................................... 16 Changes to Ordering Guide .......................................................... 16 12/06--Rev. 0 to Rev. A Change to Thermal Characteristics Section ................................. 4 Changes to Outline Dimensions................................................... 16 Changes to Ordering Guide .......................................................... 16 10/04--Revision 0: Initial Version Rev. C | 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 Min 2.6 1 Max 5.5 5 Unit V mA 5 1.5 A MHz 3.33 3.36 40 4.77 4.81 40 V V mV V V mV 0.3 1.18 120 5% 0.15 1.2 3.5 8.0 % V ILED = 20 mA, VFB = 0.4 V V mA kHz ISET = 15 mA 1x mode 1.5x mode 2x mode 2.6 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 LED CURRENT PWM 1 DIGITAL INPUTS Input High Input Low Input Leakage Current CHARGE PUMP POWER EFFICIENCY VOUT RIPPLE Typ 20 200 0.1 0.7 VCC V 0.3 VCC 1 88 30 V A % mV Guaranteed by design. Not 100% production tested. Rev. C | Page 3 of 16 Test Conditions All four LEDs disabled, VCC = 3.3 V, RSET = 7.08 k, CTRL1 = 1, CRTL2 = 1 CTRL1 = 1, CRTL2 = 1, VCC = 3.4 V, VFB = 0.2 V, IFB = 20 mA VCC = 3.6 V, ILED = 20 mA, all four LEDs enabled 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 Short through LED. Based on long-term current density limitations. 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 (CP-16-3) package: JA =50C/W ESD CAUTION Rev. C | Page 4 of 16 ADM8843 FB4 8 9 GND NOTES 1. CONNECT THE EXPOSED PADDLE TO GND. 05050-003 14 C1- 10 GND FB3 7 11 C2- TOP VIEW (Not to Scale) FB1 5 GND 4 12 CTRL2 ADM8843 FB2 6 ISET 3 13 CTRL1 16 C1+ PIN 1 INDICATOR VOUT 1 C2+ 2 15 VCC PIN CONFIGURATION AND FUNCTION DESCRIPTIONS Figure 2. Pin Configuration Table 3. Pin Function Descriptions Pin No. 1 2 3 Mnemonic VOUT C2+ ISET 4, 9, 10 5 to 8 GND FB1 to FB4 11 12 13 14 15 16 - C2- CTRL2 CTRL1 C1- VCC C1+ EP 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 provide 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 to 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. Rev. C | Page 5 of 16 ADM8843 TYPICAL PERFORMANCE CHARACTERISTICS 20.35 35 20.30 30 LED CURRENT (mA) 25 20 15 10 +25C 20.15 +85C 20.10 10.75 8.75 RSET (k) 6.75 12.75 14.75 05050-004 20.05 5 4.75 20.00 2.6 4.1 3.6 4.6 SUPPLY VOLTAGE (V) 3.1 5.1 5.6 Figure 6. ILED (mA) vs. Temperature (C), Four LEDs Enabled Figure 3. ILED (mA) vs. RSET 35 20.24 20.22 30 LED CURRENT (mA) 20.20 LED CURRENT (mA) 20.20 05050-007 LED CURRENT (mA) -40C 20.25 20.18 20.16 20.14 25 20 15 20.12 10 0 40 TEMPERATURE (C) 80 5 2.6 05050-005 20.08 -40 3.0 3.4 3.8 4.2 4.6 SUPPLY VOLTAGE (V) 5.0 5.4 05050-008 20.10 Figure 7. ILED (mA) vs. Supply Voltage (V) Figure 4. ILED (mA) Variation over Temperature (C), VCC = 3.6 V 95 20 90 85 EFFICIENCY (%) 12 8 80 75 70 4 60 0 0 20 40 60 DUTY CYCLE (%) 80 100 0 10 20 30 40 50 60 DUTY CYCLE (%) 70 80 90 100 05050-009 65 05050-006 LED CURRENT (mA) 16 Figure 8. LED Efficiency vs. Varying Duty Cycle of 1 kHz PWM Signal, Four LEDs Enabled, 20 mA/LED Figure 5. ILED (mA) vs. PWM Dimming (Varying Duty Cycle), Four LEDs Enabled, Frequency = 1 kHz Rev. C | Page 6 of 16 ADM8843 180 -40C CTRL1/2 SUPPLY CURRENT (mA) 160 +25C +85C 1 140 CURRENT 120 2 100 VOUT 5050-013 80 3.0 3.4 3.8 4.2 4.6 SUPPLY VOLTAGE (V) 5.0 5.4 05050-010 3 60 2.6 VOUT 1 CH2 160mA W B W M 10.0s CH2 -2.44mV VCC 1 VOUT 2 CH1 20.0mV B W CH2 20.0mV B W M 10.0s CH1 05050-014 05050-011 2 B Figure 12. Soft Start Showing the Initial In-Rush Current and VOUT Variation, Four LEDs @ 20 mA/LED, VCC = 3.6 V Figure 9. Supply Current vs. Supply Voltage over Temperature, Four LEDs Enabled @ 20 mA/LED VCC CH1 2.00V CH3 1.00V CH1 20.0mV -12.8mV B W CH2 20.0mV B W M 400ns CH2 2.4mV Figure 13. 2x Mode Operating Waveforms Figure 10. 1.5x Mode Operating Waveforms 90 VF = 3.8V 85 VF = 4.0V 1 70 65 60 55 50 2 VF = 3.6V VF = 3.2V 45 5050-012 VOUT VF = 4.3V 75 CH1 20.0mV B W CH2 20.0mV B W M 400ns CH2 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 (V) 2.4mV Figure 14. Power Efficiency vs. Supply Voltage over Li-Ion Range, Four LEDs @ 20 mA/LED Figure 11. 1x Mode Operating Waveforms Rev. C | Page 7 of 16 5050-015 VCC POWER EFFICIENCY (%) 80 ADM8843 85 VF = 3.8V 80 VF = 4.0V 75 VF = 4.3V C2 FALL : 44.0ms @: -44.4ms 200s LOW SIGNAL AMPLITUDE CTRL1/2 70 1 65 60 VOUT 55 VF = 3.6V 50 VF = 3.2V 45 VCC (V) Figure 15. Power Efficiency vs. Supply Voltage over Li-Ion Range, Four LEDs @ 15 mA/LED 05050-017 2 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 05050-016 POWER EFFICIENCY (%) 90 CH1 2.00V CH2 2.00mV M 10.0ms CH2 Figure 16. TPC Delay Rev. C | Page 8 of 16 4.36mV 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 among 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). 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 separate current sinks to sense each LED current individually 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). Soft start 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. Table 4. Shutdown Truth Table 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 ADM8843 ISET R = 15k RSET = 13.4k 05050-022 VBRIGHT 0V-2.5V Figure 17. PWM Brightness Control Using a DC Voltage Applied to VBRIGHT C1 1F VCC C2 1F ADM8843 VOUT CHARGE PUMP 1x/1.5x/2x MODE C4 4.7F C3 2.2F MAIN SUB OSC CTRL1 CTRL2 CONTROL LOGIC VREF CURRENT CONTROLLED SINKS GND Figure 18. Functional Block Diagram Rev. C | Page 9 of 16 05050-001 RSET LED CURRENT CONTROL CIRCUIT CURRENT CONTROL 4 ISET CURRENT CONTROL 3 FB1 FB2 FB3 FB4 CURRENT CONTROL 2 CTRL2 0 1 0 1 CURRENT CONTROL 1 CTRL1 0 0 1 1 ADM8843 Applying a digital PWM signal to one or both digital input control pins, CTRL1 and CTRL2, adjusts 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. 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. The brightness of the ADM8843's main and sub displays can be controlled together or separately. This is achieved 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%. Table 5. Charge Pump Switching Thresholds Gain 1.5x to 2x 2x to 1.5x 1x to 1.5x 1.5x to 1x Threshold (V) 3.33 3.36 4.77 4.81 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. 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 one or both digital input control pins, CTRL1 and 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 may 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, that is 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, which is half the programmed LED current. C1 1F VOUT VCC C3 2.2F ADM8845 PWM INPUT OR HIGH/LOW CTRL1 PWM INPUT OR HIGH/LOW CTRL2 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 and main displays are 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). C2 1F 3.4V I IN 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. If digital PWM brightness control of the LEDs is not required, a constant Logic Level 1 (VCC) or Logic Level 0 (GND) must be applied. FB1 FB2 FB3 FB4 Figure 19. Digital PWM Brightness Control Application Diagram 05050-018 ISET RSET 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. Rev. C | 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 display 4, 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 display5 1 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 only the main display is off. CTRL2 = 0 means a constant logic level (GND) is applied to CTRL2. 3 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 only the sub display LEDs 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. 2 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 100% 80% 50% SHDN 37ms > tCP > 15ms Figure 20. Application Timing Rev. C | Page 11 of 16 05050-020 MAIN DISPLAY BRIGHTNESS ADM8843 LED BRIGHTNESS CONTROL USING A PWM SIGNAL APPLIED TO VPWM LED BRIGHTNESS CONTROL USING A DC VOLTAGE APPLIED TO VBRIGHT 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, and 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, and 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 only be 0 V and 2.5 V to result in 20 mA flowing in each LED. 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 an amplitude of 0 V to 2.5 V applied to VBRIGHT. (1 - Duty Cycle) I SET _ Voltage x 120 x R SET x 2R 100 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 R SET + 2R 20mA 7.2mA ILED 100% = ILED = 0mA 0% = ILED = 20mA 0mA ADM8843 Figure 22. PWM Brightness Control Application Diagram Using a DC Voltage Applied to VBRIGHT ISET VPWM 0V-2.5V R = 7.5k R = 7.5k C5 = 1F RSET = 13.4k Figure 21. PWM Brightness Control Using Filter-PWM Signal Rev. C | Page 12 of 16 05050-023 13.6mA 05050-021 I LED = The equation for ILED is ADM8843 APPLICATIONS LAYOUT CONSIDERATIONS AND NOISE DRIVING FOUR LEDS IN THE MAIN DISPLAY ONLY 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. 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. WHITE LED SHORTING 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. 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 current sinks to produce the LED current. If an LED is shorted, the ADM8843 continues to sink (ISET x 120 mA). DRIVING FEWER THAN FOUR LEDS LCD MAIN DISPLAY VCC 2.6V-5.5V VCC 2.6V-5.5V VOUT VOUT ADM8843 ADM8843 FB1 FB2 FB3 FB4 GND ISET 05050-024 RSET GND RSET Figure 24. Driving Three White LEDs Figure 23. Driving Four White LEDs MAIN DISPLAY SUB DISPLAY VCC 2.6V-5.5V VOUT ADM8843 FB1 FB2 FB3 FB4 CTRL1 CTRL2 ISET GND 05050-002 ISET FB1 FB2 FB3 FB4 CTRL1 CTRL2 05050-025 CTRL1 CTRL2 RSET Figure 25. Typical Application Diagram Rev. C | 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 Option 2 Input and output ripple plots for 1x and 1.5x modes of operation are shown with C1, C2 = 0.22 F; C3 = 0.47 F; and C4 = 1 F. Input and output ripple plots for 1x and 1.5x modes of operation are shown with C1, C2 = 0.22 F; C3 = 0.47 F; and C4 = 4.7 F. 2 VOUT 3 2 VOUT 3 CH2 10.0mV B B W M 400ns CH3 -33mV CH2 10.0mV CH3 10.0mV W Figure 26. 1x Mode Operation, Four LEDs with 20 mA/LED at VCC = 5.0 V, with a 1 F VCC Decoupling Capacitor 2 VOUT 3 B W M 1.00s CH3 -33mV W Figure 28. 1x Mode Operation, Four LEDs with 20 mA/LED at VCC = 5.0 V, with a 4.7 F VCC Decoupling Capacitor VCC 2 VOUT 3 05050-027 VCC B 05050-029 CH3 10.0mV 05050-028 05050-026 VCC VCC CH2 20.0mV CH3 50.0mV B B W M 400ns CH3 CH2 20.0mV -33mV CH3 50.0mV W Figure 27. 1.5x Mode Operation, Four LEDs with 20 mA/LED at VCC = 3.6 V, with a 1 F VCC Decoupling Capacitor B B W M 400ns CH3 -33mV W Figure 29. 1.5x Mode Operation, Four LEDs with 20 mA/LED at VCC = 3.6 V, with a 4.7 F VCC Decoupling Capacitor Rev. C | Page 14 of 16 ADM8843 POWER EFFICIENCY The ADM8843 power efficiency () equations are as follows: Example 2 = POUT/PIN PIN = ((VCC x ILOAD x Gain) + (IQ x VCC)) POUT = 4 x (VF x ILED) 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 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). POUT = 4(VF x ILED) POUT = 4(3.6 V x 20 mA) POUT = 0.288 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. = POUT/PIN = 0.288/0.41684 = 70 % 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 ILOAD IIN VOUT VCC ADM8843 FB1 FB2 FB3 FB4 CTRL1 CTRL2 ISET GND 05050-019 RSET 7.32k Figure 30. Charge Pump Power Efficiency Diagram, Example 1 Rev. C | Page 15 of 16 ADM8843 OUTLINE DIMENSIONS 0.60 MAX 3.00 BSC SQ BOTTOM VIEW 13 12 0.45 2.75 BSC SQ TOP VIEW 0.80 MAX 0.65 TYP 12 MAX SEATING PLANE 0.05 MAX 0.02 NOM 0.30 0.23 0.18 1 1.50 SQ 1.35 EXPOSED PAD 0.50 BSC 0.90 0.85 0.80 16 PIN 1 INDICATOR *1.65 9 4 8 5 0.25 MIN 1.50 REF FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. 0.20 REF *COMPLIANT TO JEDEC STANDARDS MO-220-VEED-2 EXCEPT FOR EXPOSED PAD DIMENSION. 07-17-2008-A PIN 1 INDICATOR 0.50 0.40 0.30 Figure 31. 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 3 mm x 3 mm Body, Very Thin Quad (CP-16-3) Dimensions shown in millimeters ORDERING GUIDE Model1 ADM8843ACPZ-REEL7 ADM8843EB-EVALZ 1 Temperature Range -40C to +85C Package Description 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ] Evaluation Board Z = RoHS Compliant Part. (c)2004-2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05050-0-1/11(C) Rev. C | Page 16 of 16 Package Option CP-16-3 Branding M2U Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Analog Devices Inc.: ADM8843ACPZ-REEL7 ADM8843EB-EVALZ