ADD8702ACP-REEL7 AD [Analog Devices], ADD8702ACP-REEL7 Datasheet - Page 7

• Manufacturer Part Number: ADD8702ACP-REEL7
• Description: 12-Channel Gamma Buffers with Vcom Buffer
• Manufacturer: AD [Analog Devices]

APPLICATIONS
Figure 1 is a block diagram of the configuration of an XGA-
compatible (1024
providing gamma correction reference voltages to the source
drivers and an integrated V
Panel size and resolution determine the number of gamma
reference voltages required. For a 256-grayscale level, 8-bit color
scheme, 6
match the characteristics of the LCD driver to the characteristics
of the actual LCD panel for improved picture quality. External
reference gamma correction voltages are often generated using
a simple resistor ladder. Using the ADD8702, the resistor
ladder is incorporated in the IC for reduced cost and number
of components.
5V
The ADD8702 is designed to meet the rail-to-rail capability
needed by the application, yet offers the lowest cost per channel
solution. The ADD8702 gamma buffers offer 10 mA continuous
drive current capability. To be more competitive, the design
maximizes the die area by allowing specific channels to swing to
the positive rail and negative rail. So it is imperative that the
channels swinging close to the supply rail be used for the posi-
tive gamma references and the channels swinging close to GND
be used for the negative gamma references. The V
handle up to 35 mA continuous output current and can drive up
to 1,000 pF pure capacitive load. Provision is available to adjust
the V
example of an application circuit for adjusting the output of the
V
REV. 0
COM
COM
Figure 3. Transient Load Regulation Test Circuit
Figure 2. Bandwidth Measurement Information
buffer.
16V
voltage to a desired level. Refer to Figure 4 for an
BUFFER
2 external reference nodes should be sufficient to
33
768) TFT color panel with the ADD8702
16V
BUFFER
COM
1k
driver for LCD common node.
R
NULL
V
TH
C
T
R
L
0.1 s
COM
V
TH
buffer can
10V
5V
0V
–7–
VGMA1
VGMA2
VGMA3
VGMA4
VGMA5
VGMA6
VGMA7
VGMA8
VGMA9
VGMA10
VGMA11
VGMA12
V
V
(0 ≤
COM
Table I. ADD8702 – 000 Mask Option, Resistor Tap Points
COM
GND
V
ADJUST
V
V
V
DD
V
HIGH
V
V
V
V
V
V
V
V
IN
IN
LOW
IN
IN
IN
IN
IN
IN
IN
IN
11
10
≤ 500) V
9
8
7
6
5
4
3
2
32k
Tap Point ( )
8
57
84
115
139
194
218
298
371
418
442
488
200
DD
Figure 4. Application Circuit
= 12.5 V, V
2k
V
ADD8702
COM
A12
A11
A10
A9
A8
A7
A6
A5
A4
A3
A2
A1
AMP
HIGH
= 12.5 V, and V
Voltage
0.2
1.43
2.11
2.89
3.48
4.86
5.45
7.45
9.29
10.45
11.04
12.2
5
LCD SOURCE DRIVER
ADD8702
LCD COMMON PLANE
LOW
GMA 12
GMA 11
GMA 10
GMA 9
GMA 8
GMA 7
GMA 6
GMA 5
GMA 4
GMA 3
GMA 2
GMA 1
Unit
V
V
V
V
V
V
V
V
V
V
V
V
V
= GND