Lcd Back Light Illumination - LG KE820 Service Manual

3. TECHNICAL BRIEF

3.10. LCD back light illumination

Employed the AAT2805 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.
R434
FLASH_EN
LCD_BACKLIGHT
Figure 17 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
C201
VBAT
1u
U202
4
VIN
C206
1u
9
GND
17
PGND
0
16
EN_FLSH
10
EN_SET
R211 R212
100K 100K
- 46 -
C202 C203
1u 1u R201
R205
R206
3 R209
VOUT_FL
13
VOUT_BL
5
ISINK1
6
ISINK2
7
ISINK3
8
ISINK4
AAT2805IXN-4.5-T1
C214 C215
2.2u 1u
120
120
120
120
FLASH_LEDA
MLED_A
MLED_C1
MLED_C2
MLED_C3
MLED_C4