Lcd Back-Light Illumination - LG Prada KE850 Service Manual

3.10. LCD back-light illumination

Employed the AAT2806 is a dual charge pump designed to support both the white LED backlight and
flash applications for systems operating with lithium-ion/polymer batteries. The backlight charge pump
is capable of driving up to four LEDs at a total of 80mA. The current sinks may be operated individually
or in parallel for driving higher current LEDs. To maximize power efficiency, the charge pump operates
in 1X, 1.5X, or 2X mode, where the mode of operation is automatically selected by comparing the
forward voltage of each LED with the input voltage.
FLASH_EN
LCD_BACKLIGHT
R130
100K
Figure 15 LCD Back light unit and Flash LED charge pump IC
The interface relies on the number of rising edges of the EN/SET pin to address and load the registers.
S2Cwire latches data or address after the EN/SET pin has been held high for time TLAT. The interface
records rising edges of the EN/SET pin and decodes them into 16 different states, as indicated in table
C131 C132 C133
VBAT
1u 1u 1u
4
VIN VOUT_FL
C134 VOUT_BL
1u
9
U108
GND
17 AAT2806IXN-4.5-T1
PGND
16
EN_FLSH
10
EN_SET
R131
100K
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3. TECHNICAL BRIEF
3
13
C135
1u
5
ISINK1
6
ISINK2
7
ISINK3
8
ISINK4
C136
1u
FLASH_LED
MLED
MLED1
MLED2
MLED3
MLED4