Charge Pump Driver for LCD White LED Backlights ADM8845 FEATURES GENERAL DESCRIPTION Drives 6 LEDs from 2.6 V to 5.5 V (Li-Ion) input supply 1×/1.5×/2× fractional charge pump to maximize power efficiency 1% max 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 × 3 mm) Package height only 0.9 mm Low power shutdown mode Shutdown function Soft-start limiting in-rush current The ADM8845 uses charge pump technology to provide the power required to drive up to six LEDs. The LEDs are used for backlighting a color LCD display, having regulated constant current for uniform brightness intensity. The main display can have up to four LEDs, and the sub display can have one or two LEDs. The digital CTRL1 and CTRL2 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 a 1×, 1.5×, or 2× mode. The charge pump automatically switches between 1×/1.5×/2× 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 lights Micro TFT color displays DSC PDAs Improved brightness matching of the LEDs is achieved by a feedback pin to sense individual LED current with a maximum matching accuracy of 1%. FUNCTIONAL BLOCK DIAGRAM C1 1µF VCC C2 1µF ADM8845 VOUT CHARGE PUMP 1×/1.5×/2× MODE C4 4.7µF C3 2.2µF MAIN SUB OSC CTRL1 CTRL2 CONTROL LOGIC VREF 04867-0-001 CURRENT CONTROL 6 CURRENT CONTROL 5 CURRENT CONTROL 4 CURRENT CONTROL 3 RSET LED CURRENT CONTROL CIRCUIT CURRENT CONTROL 2 ISET CURRENT CONTROL 1 FB1 FB2 FB3 FB4 FB5 FB6 CURRENT CONTROLLED SINKS 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 © 2004 Analog Devices, Inc. All rights reserved. ADM8845 TABLE OF CONTENTS Specifications......................................................................................3 Absolute Maximum Ratings.............................................................4 Thermal Characteristics .............................................................. 4 ESD Caution.................................................................................. 4 Pin Configuration and Function Description ...............................5 Typical Performance Characteristics ..............................................6 Theory of Operation ...................................................................... 10 Output Current Capability ........................................................ 11 Automatic Gain Control............................................................ 11 Current Matching....................................................................... 11 Brightness Control with a Digital PWM Signal ..................... 11 LED Brightness Control Using a PWM Signal Applied to VPWM ............................................................................................. 13 LED Brightness Control Using a DC Voltage Applied to VBRIGHT .......................................................................................... 13 Applications......................................................................................14 Layout Considerations and Noise ............................................ 14 White LED Shorting .................................................................. 14 Driving Fewer than Six LEDs ................................................... 14 Driving Flash LEDs.................................................................... 15 Driving Camera Light, Main, and Sub LEDs.......................... 15 Driving Four Backlight White LEDs and Flash LEDs........... 16 Power Efficiency......................................................................... 17 Outline Dimensions ........................................................................18 Ordering Guide .......................................................................... 18 REVISION HISTORY 10/04—Revision 0: Initial Version Rev. 0 | Page 2 of 20 ADM8845 SPECIFICATIONS VCC = 2.6 V to 5.5 V; TA = −40°C to +85°C, unless otherwise noted; C1,C2 = 1.0 µF; C3 = 2.2 µF; C4 = 4.7 µF Table 1. Parameter INPUT VOLTAGE, VCC SUPPLY CURRENT, ICC SHUTDOWN CURRENT CHARGE PUMP FREQUENCY CHARGE PUMP MODE THRESHOLDS 1.5× to 2× Accuracy 2× to 1.5× Accuracy Hysteresis 1× to 1.5× Accuracy 1.5× to 1× Accuracy Hysteresis ISET PIN LED : LED Matching LED : ISET Accuracy Min 2.6 2.6 Max 5.5 5 Unit V mA 5 µA MHz 1.5 3.33 4 3.36 4 40 4.77 4 4.81 4 40 −1 −1 ISET Pin Voltage ILED to ISET Ratio MIN COMPLIANCE ON FBx PIN Charge Pump Output Resistance LED Current PWM DIGITAL INPUTS Input High Input Low Input Leakage Current CHARGE PUMP POWER EFFICIENCY VOUT RIPPLE Typ +1 +1 1.18 120 0.2 1.2 3.5 8.0 0.1 V % V % mV V % V % mV % % 0.3 1.8 5.1 14 30 200 0.3 VCC 1 V Ω Ω Ω mA kHz V V µA % mV _______________________ 1 All six LEDs disabled, VCC = 3.3 V, RSET = 7.08 kΩ CTRL1 = 1, CRTL2 = 1 ILED = 20 mA, VFB =0.4 V ILED = 20 mA, RSET = 7.08 kΩ, VFB = 0.4 V, VCC = 3.6 V, TA = 25°C V 0.5 VCC 88 30 Test Conditions Guaranteed by design. Not 100% production tested. Rev. 0 | Page 3 of 20 ISET = 20 mA 1× mode 1.5× mode 2× mode See Note 1 and Figure 21 CTRL1 = 1, CRTL2 = 1, VCC = 3.4 V, VFB = 0.2 V, IFB = 20 mA VCC = 3.6 V, ILED = 20 mA, all six LEDs enabled ADM8845 ABSOLUTE MAXIMUM RATINGS TA = 25°C, unless otherwise noted. Table 2. Parameter Supply Voltage, VCC ISET CTRL1, CTRL2 VOUT Shorted1 Feedback pins FB1 to FB6 Operating Temperature Range Six LEDs Enabled with 30 mA/LED2 Six LEDs Enabled with 20 mA/LED2 VOUT3 Storage Temperature Range Power Dissipation ESD Class 1 2 3 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 –40°C to +65°C –40°C to +85°C 180 mA –65°C to +125°C 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: θJA = 50°C/W Short through LED. LED current should be derated above TA > 65°C, refer to Figure 21. 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 20 ADM8845 12 CTRL2 11 C2– 10 GND 04867-0-003 9 FB6 FB5 8 14 C1– FB4 7 TOP VIEW (Not to Scale) FB2 5 FB1 4 ADM8845 FB3 6 ISET 3 13 CTRL1 PIN 1 INDICATOR VOUT 1 C2+ 2 15 VCC 16 C1+ PIN CONFIGURATION AND FUNCTION DESCRIPTION Figure 2. Pin Configuration Table 3. Pin Function Descriptions Pin No. 1 Mnemonic VOUT 2 3 C2+ ISET 4–9 FB1–FB6 10 11 12 13 14 15 16 - GND C2− CTRL2 CTRL1 C1− VCC C1+ EP Function Charge Pump Output. A 2.2 µF 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 RSET, ISET, is gained up by 120 to give the ILED current. Connect RSET to GND to set the bias current as VSET/RSET. Note that VSET = 1.18 V. LED1–LED6 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 six LEDs, this pin can be left unconnected or connected to GND. Device Ground Pin. 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 µF decoupling capacitor. Flying Capacitor 1 Positive Connection. Expose Paddle. Connect the exposed paddle to GND. Rev. 0 | Page 5 of 20 ADM8845 TYPICAL PERFORMANCE CHARACTERISTICS 0.4 35 0.3 MAX POSITIVE MATCHING ERROR 30 25 20 15 0.1 0 –0.1 –0.2 10 MAX NEGATIVE MATCHING ERROR 5 4.75 6.75 10.75 8.75 RSET (kΩ) 12.75 04867-0-004 –0.3 14.75 –0.4 2.6 3.0 3.4 3.8 4.2 4.6 SUPPLY VOLTAGE (V) 5.0 5.4 04867-0-007 MATCHING ERROR (%) LED CURRENT (mA) 0.2 Figure 6. ILED (mA) Matching Error (%) vs. Supply Voltage (V), TA = 25°C and ILED = 20 mA Figure 3. ILED (mA) Current vs. RSET 20.35 20.24 20.30 20.22 20.20 20.25 LED CURRENT (mA) LED CURRENT (mA) –40°C 20.20 25°C 20.15 85°C 20.10 20.18 20.16 20.14 20.12 20.05 4.1 3.6 4.6 SUPPLY VOLTAGE (kΩ) 5.1 5.6 20.08 –40 Figure 4. ILED (mA) vs. Temperature (°C), Six LEDs Enabled 40 TEMPERATURE (°C) 80 Figure 7. ILED (mA) Variation over Temperature (°C), VCC = 3.6 V 35 0.2 30 LED CURRENT (mA) 0.3 0.1 0 –0.1 –0.2 25 20 15 –0.3 –40 –20 25 0 45 TEMPERATURE (°C) 65 85 04867-0-006 10 5 2.6 Figure 5. ILED Matching (%) over Temperature (°C), VCC = 3.6 V, ILED = 20 mA, Six LEDs Enabled Rev. 0 | Page 6 of 20 3.0 3.4 3.8 4.2 4.6 SUPPLY VOLTAGE (V) 5.0 Figure 8. ILED (mA) vs. Supply Voltage (V) 5.4 04867-0-009 % ERROR 0 04867-0-008 3.1 04867-0-005 20.10 20.00 2.6 ADM8845 95 20 90 85 EFFICIENCY (%) LED CURRENT (mA) 16 12 8 80 75 70 4 0 20 40 60 DUTY CYCLE (%) 80 100 60 0 Figure 9. ILED (mA) vs. PWM Dimming (Varying Duty Cycle), Six LEDs Enabled, Frequency = 1 kHz 10 20 30 40 50 60 DUTY CYCLE (%) 70 80 90 100 04867-0-013 0 04867-0-010 65 Figure 12. LED Efficiency vs. Varying Duty Cycle of 1 kHz PWM Signal, Six LEDs Enabled, 20 mA/LED 300 CTRL1/2 200 20mA/LED 1 150 CURRENT 15mA/LED 2 100 VOUT 50 3.0 3.4 3.8 4.2 4.6 SUPPLY VOLTAGE (V) 5.0 5.4 3 04867-0-011 0 2.6 Figure 10. Input Current vs. Supply Voltage, Six LEDs Enabled CH1 2.00V CH3 1.00V B CH2 160mA W B W M 5.00µs CH2 180mV Figure 13. Soft Start Showing the Initial In-Rush Current and VOUT Variation, Six LEDs @ 20 mA/LED, VCC = 3.6 V VCC 1 2 VCC 1 VOUT 2 CH1 20.0mV B W CH2 20.0mV B W M 400ns CH1 04867-0-015 04867-0-012 VOUT 04867-0-014 SUPPLY CURRENT ICC (mA) 250 220mV CH1 20.0mV Figure 11. 1.5× Mode Operating Waveforms B W CH2 20.0mV B W M 400ns CH1 Figure 14 .2× Mode Operating Waveform Rev. 0 | Page 7 of 20 220mV ADM8845 90 VF = 3.6V 85 VF = 4.0V 1 VOUT 2 VF = 4.3V 75 70 65 60 55 VF = 3.8V 04867-0-016 50 CH1 20.0mV B W CH2 20.0mV B W M 400ns CH1 VF = 3.2V 45 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 220mV VCC Figure 15. 1× Mode Operating Waveforms 04867-0-019 VCC POWER EFFICIENCY 80 Figure 18. Power Efficiency vs. Supply Voltage over Li-Ion Range, Six LEDS @ 20 mA/LED 90 90 VF = 3.8V VF = 4.0V POWER EFFICIENCY 75 70 65 60 VF = 3.6V VF = 3.8V 75 70 65 60 55 VF = 3.6V 50 VF = 3.2V VF = 3.2V 45 45 VCC 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 04867-0-017 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 04867-0-020 POWER EFFICIENCY VF = 4.3V 50 VF = 4.0V 80 80 55 VF = 4.3V 85 85 Figure 19. Power Efficiency vs. Supply Voltage over Li-Ion Range Four LEDS @ 20 mA/LED Figure 16. Power Efficiency vs. Supply Voltage over Li-ion Range, Six LEDS @ 15 mA/LED 85 VF = 3.8V 80 VF = 4.0V 75 VF = 4.3V C2 FALL ∆: 44.0ms @: –44.4ms 200µs LOW SIGNAL AMPLITUDE CTRL1/2 1 70 65 VOUT 60 55 VF = 3.6V VF = 3.2V 2 45 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 04867-0-021 50 04867-0-018 POWER EFFICIENCY 90 CH1 2.00V CH2 2.00V M10.0ms Figure 20. TPC Delay Figure 17. Power Efficiency vs. Supply Voltage over Li-Ion Range, Four LEDS @ 15 mA/LED Rev. 0 | Page 8 of 20 CH2 4.36V ADM8845 30mA 65°C 85°C 04867-0-022 20mA Figure 21. Maximum ILED (mA) vs. Ambient Temperature, Six LEDs Connected Rev. 0 | Page 9 of 20 ADM8845 THEORY OF OPERATION The ADM8845 charge pump driver for LCD white LED backlights implements a multiple gain charge pump (1×, 1.5×, 2×) 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 1×/1.5×/2× 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 ADM8845’s six LEDs are arranged into two groups, main and sub. The main display can have up to four LEDs (FB1 to FB4), and the sub display can have one or two LEDs (FB5 and FB6) (see Figure 23). Two digital input control pins, CTRL1 and CTRL2, 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 ADM8845 to produce the ILED currents of up to 30 mA/LED (ILED = ISET × 120 and ISET = 1.18 V/RSET). The ADM8845 uses six individual current sinks to individually sense each LED current with a maximum matching performance of 1%. This current matching performance ensures uniform brightness across a color display. The ADM8845 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 ADM8845 also allows the brightness of the white LEDs to be controlled using a dc voltage (see Figure 22). Softstart circuitry limits the in-rush current flow at power-up. The ADM8845 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 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 ADM8845 ISET R = 15kΩ RSET = 13.4kΩ 04867-0-027 VBRIGHT 0V–2.5V Figure 22. PWM Brightness Control Using a DC Voltage Applied to VBRIGHT C1 1µF VCC C2 1µF ADM8845 VOUT CHARGE PUMP 1×/1.5×/2× MODE C4 4.7µF C3 2.2µF MAIN SUB OSC CTRL1 CTRL2 CONTROL LOGIC VREF CURRENT CONTROLLED SINKS GND Figure 23. Functional Block Diagram Rev. 0 | Page 10 of 20 04867-0-001 CURRENT CONTROL 6 CURRENT CONTROL 5 CURRENT CONTROL 4 RSET LED CURRENT CONTROL CIRCUIT CURRENT CONTROL 3 ISET CURRENT CONTROL 2 FB1 FB2 FB3 FB4 FB5 FB6 CURRENT CONTROL 1 CTRL1 0 0 1 1 ADM8845 OUTPUT CURRENT CAPABILITY CURRENT MATCHING The ADM8845 can drive up to 30 mA of current to each of the six LEDs given an input voltage of 2.6 V to 5.5 V. The LED currents have a maximum current matching of 1% between any two LED currents. An external resistor, RSET, sets the output current, approximated by the following equation: The 1% maximum current matching performance is defined by the following equations: RSET = 120 × (1.18 V/ILED) Table 5. ILED, RSET, and Compliance Table Typ. Compliance 0.17 V 0.20 V 0.34 V When the ADM8845 charge pump is loaded with 180 mA (six LEDs at 30 mA/LED), the ambient operating temperature is reduced (see Figure 21). AUTOMATIC GAIN CONTROL The automatic gain control block controls the operation of the charge pump by selecting the appropriate gain for the charge pump. This 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 6. Table 6. Charge Pump Switching Thresholds Gain 1.5× to 2× 2× to 1.5× 1× to 1.5× 1.5× to 1× where IMAX is the largest ILED current, and IMIN is the smallest ILED current. BRIGHTNESS CONTROL WITH A DIGITAL PWM SIGNAL 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 ADM8845, 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 1µF C2 1µF VOUT ADM8845 PWM INPUT OR HIGH/LOW CTRL1 PWM INPUT OR HIGH/LOW CTRL2 Threshold 3.33 V 3.36 V 4.77 V 4.81 V ISET C3 2.2µF FB1 FB2 FB3 FB4 FB5 FB6 RSET 04867-0-024 where VF is the LED forward voltage. For 20 mA/LED, the compliance is 0.20 V typ and 0.30 V max (see Table 5). RSET 9.44 kΩ 7.08 kΩ 4.72 kΩ Min Matching Error = [(IMIN – IAVG)/IAVG] × 100 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 either at zero current or full current (set by RSET). VOUT – VF ≥ Compliance 15 mA 20 mA 30 mA Max Matching Error = [(IMAX – IAVG)/IAVG] × 100 or To regulate the LED currents properly, sufficient headroom voltage (compliance) must be present. The compliance refers to the minimum amount of voltage that must be present across the internal current sinks to ensure that the desired current and matching performance is realizable. To ensure that the desired current is obtained, use the following equation to find the minimum input voltage required: ILED IAVG = (IMAX + IMIN)/2 Figure 24. Digital PWM Brightness Control Application Diagram By applying a digital PWM signal to the digital input control pins, CTRL1 and/or CTRL2 can adjust the brightness of the sub and/or main displays. The ADM8845’s six white LEDs are organized into two groups, main display (FB1 to FB4) and sub display (FB4 to FB6); refer to the Theory of Operation section. Rev. 0 | Page 11 of 20 ADM8845 The ADM8845’s main and sub display brightness can be controlled together or separately by applying a digital PWM signal to both 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 also 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 go low, the LED current control sinks shutdown. Shutdown of the charge pump is delayed by 15 ms. This timeout period (tCP) allows the ADM8845 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 25). If digital PWM brightness control of the LEDs is not required, a constant Logic Level 1 (VCC) or 0 (GND) must be applied. The six white LED in the ADM8845 are arranged in two groups, sub and main. It is possible to configure the six LEDs as in Table 7; refer also to Figure 25. Table 7. 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 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. 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 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. 2 Rev. 0 | Page 12 of 20 ADM8845 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% MAIN DISPLAY BRIGHTNESS 80% 50% 04867-0-025 SHDN 37ms > tCP > 15ms Figure 25. Application Timing 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 on Figure 26, also can be used to control PWM brightness. This PWM brightness control method can be used instead of CTRL1 and/or CTRL2 digital PWM brightness control. With this configuration, The CTRL1 and CTRL2 digital logic pins can be used to control shutdown of the white LEDs, while VPWM can be used to control the brightness of all the white LEDs 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 ADM8845. 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 26). To have 20 mA flowing in each LED, the amplitude of the PWM signal must be 0 V and 2.5 V only. Adding one resistor, as shown in Figure 22, this configuration can also be used to control brightness the white LEDs by using a dc voltage applied to the VBRIGHT node. Figure 27 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. ISET = [(1/RSET + 1/R)(VSET)] – [(1/R)(VBRIGHT)] ILED = 120 × ISET where R = 15 kΩ and VSET = voltage at ISET pin (1.18 V). 2.5V VBRIGHT 1.6V 0.8V (1 − Duty Cycle) I _ Voltage = SET × 120 × R SET × 2R 100 0V R SET + 2R 20mA 13.6mA 7.2mA ILED 100% = ILED = 0mA 0% = ILED = 20mA 0mA ADM8845 Figure 27. PWM Brightness Control Application Diagram Using a DC Voltage Applied to VBRIGHT ISET R = 7.5kΩ R = 7.5kΩ C5 = 1µF RSET = 13.4kΩ 04867-0-026 VPWM0V–2.5V Figure 26. PWM Brightness Control Using Filtered-PWM Signal Rev. 0 | Page 13 of 20 04867-0-028 I LED The equation for ILED is ADM8845 APPLICATIONS LAYOUT CONSIDERATIONS AND NOISE DRIVING FEWER THAN SIX LEDS Because of the ADM8845’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 ADM8845. The ADM8845 can be operated with fewer than six LEDs in parallel by simply leaving the unused FBx pins floating or connected to GND. For example, Figure 28 shows five LEDs being powered by the ADM8845, and Figure 29 shows three main LEDs and one sub LED. WHITE LED SHORTING If an LED is shorted, the ADM8845 continues to drive the remaining LEDs with ILED per LED (ILED = ISET × 120 mA). This is because the ADM8845 uses six internal currents sinks to produce the LED current. If an LED is shorted, the ADM8845 continues to sink (ISET × 120 mA) as programmed by RSET through the shorted LED. LCD MAIN DISPLAY SUB DISPLAY VCC 2.6V–5.5V VCC 2.6V–5.5V VOUT VOUT ADM8845 CTRL1 CTRL2 ISET GND FB1 FB2 FB3 FB4 FB5 FB6 RSET Figure 29. Driving Three Main LEDs and One Sub LED Figure 28. Driving Five White LEDs MAIN DISPLAY SUB DISPLAY VCC 2.6V–5.5V VOUT ADM8845 CTRL1 CTRL2 ISET GND FB1 FB2 FB3 FB4 FB5 FB6 04867-0-002 GND FB1 FB2 FB3 FB4 FB5 FB6 04867-0-029 CTRL1 CTRL2 04867-0-030 ADM8845 RSET Figure 30. Typical Application Diagram Rev. 0 | Page 14 of 20 ADM8845 DRIVING FLASH LEDS DRIVING CAMERA LIGHT, MAIN, AND SUB LEDS The ADM8845 can be operated with any two FBx pins operated in parallel to double the combined LED current supplied by the ADM8845. For example, if three flash LEDs need to be driven with 60 mA/LED, the ADM8845 can be configured as in Figure 31 (see also Figure 21). The ADM8845 can also be configured to power a camera light that is composed of four white LEDs in parallel, packaged into one package. FB1 to FB4 now power the camera light, and FB5 and FB6 power the main display. The sub display LED is powered from the ADM8845 by using an external current mirror to control the current flowing through the sub white LED (see Figure 32). All white LEDs have 15 mA/LED, therefore total load on the ADM8845 charge pump is 105 mA, and the maximum load on the ADM8845 charge pump is 180 mA (see Figure 21). VCC 2.6V–5.5V VOUT ADM8845 CTRL1 CTRL2 GND 60mA 60mA 04867-0-031 RSET 4.27kΩ 60mA FB1 FB2 FB3 FB4 FB5 FB6 Figure 31. Driving Three Flash LEDs C1 1µF VCC C2 1µF ADM8845 VOUT CHARGE PUMP 1×/1.5×/2× MODE C4 4.7µF C3 2.2µF CAMERA OSC CTRL1 CTRL2 CONTROL LOGIC 15mA/LED 15mA/LED 15mA/LED R 04867-0-032 CURRENT CONTROLLED SINKS CURRENT CONTROL7 CURRENT CONTROL 6 CURRENT CONTROL 5 CURRENT CONTROL 4 CURRENT CONTROL 3 CURRENT CONTROL 2 CURRENT CONTROL 1 RSET 9.44kΩ LED CURRENT CONTROL CIRCUIT SUB VREF FB1 FB2 FB3 FB4 FB5 FB6 ISET MAIN GND Figure 32. Driving Camera Light, Two Main LEDs, and One Sub LED Rev. 0 | Page 15 of 20 ADM8845 DRIVING FOUR BACKLIGHT WHITE LEDS AND FLASH LEDS The ADM8845 also can be configured to power four backlight white LEDs and a camera flash, packaged into one package. FB1 to FB4 power the backlight light, FB5 and FB6 powers the two of the flash LEDs, and the third is powered an external current mirror to control the current flowing through the third flash LED (see Figure 33). All the backlight white LEDs have 15 mA/LED, and the flash current is 20 mA/LED. The total load on the ADM8845 charge pump is 120 mA; the maximum load on the ADM8845 charge pump is 180 mA (see Figure 21). C1 1µF C2 1µF ADM8845 VOUT CHARGE PUMP 1×/1.5×/2× MODE C4 4.7µF C3 2.2µF OSC CTRL1 CONTROL LOGIC 15mA/LED 20mA/LED CURRENT CONTROL 7 R CURRENT CONTROL 6 CURRENT CONTROL 5 CURRENT CONTROL 4 CURRENT CONTROL 3 CURRENT CONTROL 2 LED CURRENT CONTROL CIRCUIT CURRENT CONTROL 1 FB1 FB2 FB3 FB4 FB5 FB6 RSET 7.32kΩ FLASH VREF CTRL2 ISET BACKLIGHT CURRENT CONTROLLED SINKS GND Figure 33. Driving Four Backlight LEDs and Flash LED Rev. 0 | Page 16 of 20 04867-0-034 VCC CTRL1 controls the flash on/off, and CTRL2 controls the backlight on/off and brightness control. Because the RSET resistor sets the current that each of the six current control blocks can sink, a PWM signal is used to change the current in the backlight from 20 mA to 5 mA/LED. The CTRL2 duty cycle is 15/20 to give 15 mA/backlight LED. ADM8845 POWER EFFICIENCY The ADM8845 power efficiency (η) equations are Example 1 η = POUT/PIN PIN = ((VCC × ILOAD × Gain) + (IQ × VCC)) POUT = 6×(VF × ILED) The ADM8845 driving six white LED with 20 mA/LED at VCC = 3.4 V (1.5× mode), LED VF = 4.5 V. PIN = ((VCC × ILOAD × Gain) + (VCC × IQ)) PIN = ((3.4 × 120 mA × 1.5) + (3.4 × 2.6 mA)) PIN = ((0.612) + (0.00884)) PIN = 0.62084 where: IQ is the quiescent current of the ADM8845, 2.6 mA. VF is the LED forward voltage. Gain is equal to charge pump mode (1×, 1.5×, 2×). 3.4V I IN POUT = 6(VF × ILED) POUT = 6(4.5V × 20 mA) POUT = 0.54 ILOAD VOUT VCC ADM8845 η = POUT/PIN η = 0.54/0.62084 η = 87 % VCC CTRL1 ISET RSET GND FB1 FB2 FB3 FB4 FB5 FB6 Figure 34. Charge Pump Power Efficiency Diagram Examples 1 and 2 show calculations of the ADM8845 power efficiency; also see Figure 34. Example 2 04867-0-033 CTRL2 The ADM8845 driving six white LED with 20 mA/LED at VCC = 3.4 (1.5× mode), LED VF = 3.6 V. PIN = ((VCC × ILOAD × Gain) + (VCC × IQ)) PIN = ((3.4 × 120 mA × 1.5) + (3.4 × 2.6 mA)) PIN = ((0.612) + (0.00884)) PIN = 0.62084 POUT = 6(VF × ILED) POUT = 6(3.6 V × 20 mA) POUT = 0.432 η = POUT/PIN η = 0.432/0.62084 η = 70 % Rev. 0 | Page 17 of 20 ADM8845 OUTLINE DIMENSIONS 3.00 BSC SQ 0.60 MAX 0.45 PIN 1 INDICATOR TOP VIEW 2.75 BSC SQ SEATING PLANE 16 1 1.45 1.30 SQ* 1.15 EXPOSED PAD 9 (BOTTOM VIEW) 8 5 4 0.25 MIN 1.50 REF 0.80 MAX 0.65 TYP 12° MAX PIN 1 INDICATOR 13 12 0.50 BSC 0.90 0.85 0.80 0.50 0.40 0.30 0.05 MAX 0.02 NOM 0.30 0.23 0.18 0.20 REF *COMPLIANT TO JEDEC STANDARDS MO-220-VEED-2 EXCEPT FOR EXPOSED PAD DIMENSION Figure 35. 16-Lead Lead Frame Chip Scale Package [LFCSP] (CP-16) Dimensions shown in millimeters ORDERING GUIDE Model ADM8845ACP-REEL ADM8845ACP-REEL7 ADM8845ACPZ-REEL1 ADM8845ACPZ-REEL71 ADM8845ACPZ-WP1, 2 EVAL-ADM8845EB 1 2 Temperature Range −40ºC to + 85ºC −40ºC to + 85ºC −40ºC to + 85ºC −40ºC to + 85ºC −40ºC to + 85ºC Package Description 16-Lead LFCSP 16-Lead LFCSP 16-Lead LFCSP 16-Lead LFCSP 16-Lead LFCSP Evaluation Board Z = Pb-free part. WP = waffle pack. Rev. 0 | Page 18 of 20 Package Option CP-16 CP-16 CP-16 CP-16 CP-16 Branding M0P M0P M0P M0P M0P ADM8845 NOTES Rev. 0 | Page 19 of 20 ADM8845 NOTES © 2004 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04867–0–10/04(0) Rev. 0 | Page 20 of 20