12-Channel Gamma Buffers
with VCOM Buffer
ADD8702
FEATURES
FUNCTIONAL BLOCK DIAGRAM
Programmable 12-Channel Gamma Reference Generator
Mask Programmable Adjustable VCOM Buffer
Upper/Lower Outputs Swing to VDD/GND
Continuous Output Current: 10 mA
32 31 30 26 28 27 26 25
V
COM Peak Output Current: 250 mA
V
1
2
3
4
5
6
7
8
24
23
22
21
20
Outputs with Fast Settling Time for Load Change
Output Pins Are Compatible with ADD8701
Single-Supply Operation: 7 V to 16 V
Supply Current: 15 mA Max
DD
GND
V
ADJ
HIGH
V
COM
DD
V
VGMA6
VGMA5
VGMA4
V
V
11
10
IN
IN
V
V
V
9
19 VGMA3
18 VGMA2
17 VGMA1
APPLICATIONS
TFT LCD Panels
IN
8
IN
IN
7
9
10 11 12 13 14 15 16
GENERAL DESCRIPTION
The ADD8702 is a low cost, mask programmable, 12-channel
gamma reference generator, plus an adjustable VCOM driver. This
part is designed to provide gamma correction for high resolution
TFT LCD panels. The 12 gamma reference levels and VCOM are
mask programmable to 0.3% resolution using the on-chip 500
chain resistor string. This reduces component and board costs.
The output pins are compatible with the ADD8701. This allows
for single board design and fast turns for prototyping using the
initial ADD8701 board design.
The ADD8702 is specified over the temperature range of –40°C
to +85°C and comes in the 32-lead lead frame chip scale pack-
age (LFCSP) for compact board space.
The ADD8702 provides a complete programmed set of gamma
voltage references for the LCD source drivers. These references
settle quickly to load change. The VCOM output is stable with
high capacitive loads and can source or sink 250 mA peak cur-
rent. The VCOM output level can be adjusted using an external
trim-potentiometer or discrete resistors.
PANEL
TIMING
CONTROLLER
ADD8702
TIMING AND CONTROL
GAMMA
REFERENCE
VOLTAGES
GAMMA
SCAN DRIVER CONTROL
V
COM
SOURCE DRIVER
SOURCE DRIVER
NO. 2
SOURCE DRIVER
NO. 1
NO. 8
384
384
384
R
G
B
TFT COLOR PANEL
SCAN
DRIVERS
768
1024 ꢀ 768
Figure 1. Typical SVGA TFT LCD Application
REV. 0
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