ADM8845 Analog Devices, ADM8845 Datasheet
ADM8845
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ADM8845 Summary of contents
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... Charge Pump Driver for LCD GENERAL DESCRIPTION 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 ...
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... ADM8845 TABLE OF CONTENTS Features .............................................................................................. 1 Applications ....................................................................................... 1 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Revision History ............................................................................... 2 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 ...................................................................... 10 Output Current Capability ........................................................ 11 Automatic Gain Control ............................................................ 11 Current Matching ....................................................................... 11 REVISION HISTORY 1/11—Rev Rev. C Changes to Figure 18 and Figure 19 ...
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... Guaranteed by design. Not 100% production tested. See Figure 21. 200 kHz µ CTRL1 = 1, CRTL2 = 3 Rev Page 3 7.08 kΩ CC SET =0 7.08 kΩ 0 3 SET 3 0 mA, all six LEDs enabled LED ADM8845 = 25°C ...
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... ADM8845 ABSOLUTE MAXIMUM RATINGS T = 25°C, unless otherwise noted. A Table 2. Parameter Supply Voltage SET CTRL1, CTRL2 V Shorted 1 OUT Feedback Pins FB1 to FB6 Operating Temperature Range 2 Six LEDs Enabled with 30 mA/LED Six LEDs Enabled with 20 mA/LED OUT Storage Temperature Range ...
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... R SET to GND to set the bias current SET SET . When using fewer than six LEDs, this pin can be left unconnected SET Rev Page ADM8845 to the anodes of all OUT , is gained up by 120 to give the I SET . Note that V = 1.18 V. SET SET ...
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... ADM8845 TYPICAL PERFORMANCE CHARACTERISTICS 4.75 6.75 8.75 10.75 R (k) SET Figure 3. I (mA) Current vs. R LED 20.35 20.30 –40C 20.25 20.20 20.15 20.10 20.05 20.00 2.6 3.1 3.6 4.1 SUPPLY VOLTAGE (V) Figure 4. I (mA) vs. Temperature (°C), Six LEDs Enabled LED 0.3 0.2 0.1 0 –0.1 –0.2 –0.3 –40 – TEMPERATURE (C) Figure 5. I Matching (%) over Temperature (°C), V ...
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... V OUT 3 CH1 2.00V 5.0 5.4 CH3 1.00V Figure 13. Soft Start Showing the Initial In-Rush Current and OUT 220mV CH1 20.0mV Rev Page ADM8845 DUTY CYCLE (%) Six LEDs Enabled, 20 mA/LED B CH2 160mA B M 5.00µs CH2 W ...
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... ADM8845 OUT CH1 20.0mV B CH2 20.0mV B M 400ns CH1 W W Figure 15. 1× Mode Operating Waveforms 3. 3. 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 V (V) CC Figure 16. Power Efficiency vs. Supply Voltage over Li-Ion Range, Six LEDS @ 15 mA/LED ...
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... Figure 21. Maximum I (mA) vs. Ambient Temperature, LED Six LEDs Connected 85°C Rev Page ADM8845 ...
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... CC tion of the charge pump output voltage for supply voltages up to 5.5 V. The six LEDs of the ADM8845 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) ...
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... OUTPUT CURRENT CAPABILITY The ADM8845 can drive current to each of the six LEDs given an input voltage of 2 5.5 V. The LED currents have a maximum current matching of 1% between any two LED currents. An external resistor, R current, approximated by the following equation 120 × (1.18 V/I ...
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... Figure 25). If digital PWM brightness control of the LEDs is not required, a constant logic level 1 (V The six white LEDs in the ADM8845 are arranged in two groups, sub and main possible to configure the six LEDs as in Table 7. For more information, also refer to Figure 25. ...
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... LEDs, while V to control the brightness of all the white LEDs by applying a high frequency PWM signal (amplitude 2 drive an R-C-R filter on the I pin of the ADM8845 PWM SET duty cycle corresponds to 20 mA/LED, while a 100% PWM duty cycle corresponds mA/LED. At PWM frequencies above 5 kHz, C5 may be reduced (see Figure 26) ...
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... SET R SET DRIVING FEWER THAN SIX LEDs 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. ...
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... DRIVING FLASH LEDs The ADM8845 can be operated with any two FBx pins used 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). ...
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... 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 ADM8845 ...
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... × (V OUT × (4.5V × 20 mA) OUT P = 0.54 OUT η OUT η = 0.54/0.62084 η = 87% Example 2 The ADM8845 driving six white LED with 20 mA/LED 3.4 (1.5× mode), LED (( ((3.4 × 120 mA × 1.5) + (3.4 × 2.6 mA ((0.612) + (0.00884 0.62084 × ...
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... ADM8845 OUTLINE DIMENSIONS PIN 1 INDICATOR 12° MAX 1.00 0.85 0.80 SEATING PLANE ORDERING GUIDE Model 1 Temperature Range ADM8845ACPZ-REEL −40° 85°C ADM8845ACPZ-REEL7 −40° 85°C ADM8845EB-EVALZ RoHS Compliant Part. 3.00 0.60 MAX BSC SQ 0. (BOTTOM VIEW) 2.75 TOP BSC SQ EXPOSED VIEW 9 0.50 8 BSC 1.50 REF ...
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... NOTES Rev Page ADM8845 ...
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... ADM8845 NOTES ©2004–2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D04867-0-1/11(C) Rev Page ...