Lcd Back-Light Illumination - LG GX500 Service Manual

GX500 Operational Description

3.9 LCD back-light illumination

The SC654 is a high efficiency charge pump LED driver using Analogic-tech's proprietary charge pump
technology. Performance is optimized for use in single-cell Li-ion battery applications.
MLED
VBAT
C253
1u
Figure 3-17 LCD Back light unit and Flash LED charge pump IC
The LED current magnitude is controlled by the EN/SET pin using the S2Cwire interface. The interface records
rising edges of the EN/SET pin and decodes them into 32 individual current level settings. Code 1 is full scale
(31mA), and Code 32 is 0.5mA. The modulo 32 interface wraps states back to state 1 after the 32nd clock. The
counter can be clocked at speeds up to 1MHz, so intermediate states are not visible. The first rising edge of
EN/SET enables the IC and initially sets the output LED current to full scale, the lowest setting equal to 0.5mA.
Once the final clock cycle is input for the desired brightness level, the EN/SET pin should be held high to
maintain the device output current at the programmed level.
Figure 3-18 control method
Copyright © 2010 LG Electronics. Inc. All right reserved.
Only for training and service purposes
LG Electronics
LCD BACKLIGHT LED DRIVER
VA203
C255
C254 1u
1u
EVLC18S02015
1u C 252
LCD_PWM
VA205
55/143
U205 AAT3369IDT-1-T1
1
OUTCP1
18 19
OUTCP2
EP
5
2
NC
C1-
3
15
MLED6
C1+ D6
14
MLED5
D5
4 13
C2- MLED4
D4
17
12
MLED3
C2+ D3
11
MLED2
D2
6 10
IN MLED1
D1
7
16
GND EN_SET
8 9
PWM FCAP
R224
C256
47n
10K
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3. TECHNICAL BRIEF
Revision A
LCD_BL_CTRL
LGE Internal Use Only
LGE Property