BUF08800 Datasheet, PDF (14/23 Pages) Burr-Brown (TI) – Programmable Reference Generator and 400mA VCOM Driver

BUF08800
SBOS380A − FEBRUARY 2007 − REVISED MAY 2007
DIGITAL GATE-VOLTAGE (V_GH, V_GL)
ADJUSTMENT
Different panel sizes and manufacturing technology often
require different gate-high (V_GH) and gate-low (V_GL)
voltages. Optimizing the gate-high and -low voltages for
best panel performance can be time consuming. Using
channels 7 and 8, which are capable of swinging close to
GND, allows a wide range of programmable adjustment of
both V_GL and V_GH. This procedure of optimizing V_GH and
V_GL is greatly simplified and the LCD power-supply
solution can readily be used in other panels without
modification to the hardware.
TYPICAL APPLICATIONS FOR BUF08800
1. All eight channels are used for gamma correction.
The V_COM channel swings very close to V_S. It can
therefore be used to generate the highest gamma
voltage. V_COM (OUT 1) together with OUT 2 and
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OUT 3 would then form the four upper gamma
references and OUT 4 through OUT 8 would be used
for the four lower gamma references.
2. Five-channel gamma reference, two-channel gate
voltage adjust, one-channel V_COM. For applications
that can accept a total of five gamma references, the
BUF08800 can be used to digitally adjust the gate
voltages. Two channels would be used to adjust V_GH
and V_GL. In this case, the suggested use of channels
would be to use OUT 2 through OUT 6 for generating
the gamma references and OUT 7 and OUT 8 for
generating the V_GH and V_GL references. OUT 1 would
be used as the V_COM channel.
3. Six-channel gamma, one V_COM channel. For
applications requiring one V_COM channel and an even
number of gamma channels, the BUF08800 would
still be a very cost-competitive solution. Channels 2
through 7 would be used to generate the gamma
references.
36V Unregulated
V_GATE High
Programmable
R
V_GATE High
V_SD
V_S
10−Bit
DAC
D
OUT 8
10−Bit
DAC
…
…
10−Bit
DAC
OUT 7
D
SDA
SCL
Control IF
R
BUF08800
A0
V_GH = V_DIODE + OUT 8 − V_BE (NPN)
V_GH = V_DIODE + OUT 7 − V_BE (NPN)
Programmable
V_GATE Low
Unregulated
V_GATE Low
Figure 18. Using the BUF08800 to Digitally Adjust the V_GH Voltage
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