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TQFN34-20 Datasheet(PDF) 11 Page - Advanced Analogic Technologies |
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TQFN34-20 Datasheet(HTML) 11 Page - Advanced Analogic Technologies |
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11 / 20 page  AAT2847 Four-Channel Backlight Driver with Dual LDOs 2847.2007.09.1.0 11 Functional Block Diagram Tri-Mode (1x, 1.5x and 2x) Charge Pump D/A D/A D/A D/A 6 x16 bit ROM AS 2Cwire Interface 1MHz Oscillator Voltage Reference IN EN/SET GND D4 D3 D2 D1 OUT C1+ C1- C2+ C2- LDO A IN LDOA (2.8V/2.8V) FBA (NC) LDO B LDOB (1.5V/1.8V) FBB (NC) ENA 1.2V Reference AAT 2847-EE (AAT 2847-QG/-QI) (AAT 2847-QG/-QI) PGND ENB Functional Description The AAT2847 is an integrated solution for LCD dis- play applications with a built-in four channel white LED driver (charge pump) and dual 200mA LDO voltage regulators. The AAT2847 incorporates a tri-mode charge pump with load switch (1X) func- tionality and high efficiency (1.5X or 2X) perform- ance. To maximize power conversion efficiency, an internal sensing circuit monitors the voltage required at each white LED cathode input pin (D1- D4) and sets the load switch and charge pump mode based on the input battery voltage and the white LED cathode pin voltage. The voltage thresh- old for 1X to 1.5X and 1.5X to 2X mode transitions is V TH. The charge pump in the AAT2847 starts-up in 1X mode (default); under this condition, if the LED cathode input pin voltage is below V TH the AAT2847 will transition into 1.5X mode. When 1.5X mode does not provide enough current through the white LEDs for backlight applications, which occurs during the normal discharge of the input battery power source, the LED cathode input pin voltage will drop below V TH and the AAT2847 will transition into 2X mode. The charge pump requires only four external capacitors, 1µF ceramic capacitors for the flying (C1 and C2), input (C IN), and output (C OUT) capacitors. The four LED cathode input pins (D1-D4) can drive individual LEDs with a maximum current of 30mA each. The unused LED cathode input pins have to be connected to the OUT pin, otherwise the AAT2847 will operate in 2X mode only. Operating in 2X mode when it is not necessary will result in a significant reduction in efficiency. The AS 2Cwire serial interface enables the charge pump and sets the current flowing into the LED cathode input pins. The AAT2847 also contains dual LDO voltage reg- ulators that have separate enable pins from each other and the charge pump. The separate enable pins for each DC/DC device in the AAT2847 allow for every possible device operational combination. The two LDO regulators require 2.2µF output capacitors for stable operation. |
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Similar Description - TQFN34-20 |
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