BUF20800 Datasheet, PDF (15/27 Pages) Burr-Brown (TI) – 18-Channel GAMMA VOLTAGE GENERATOR with Two Programmable VCOM Channels

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CONFIGURATION FOR 20 GAMMA CHANNELS
The V_COM outputs can be used as additional gamma
references in order to achieve two additional gamma
channels (20 total). The V_COM outputs will behave the
same as the OUT1−9 outputs when sourcing or sinking
smaller currents (see the Typical Characteristics,
Figure 4). The V_COM outputs are better able to swing to the
positive rail than to the negative rail. Therefore, it is better
to use the V_COM outputs for higher reference voltages, as
shown in Figure 14.
CONFIGURATION FOR 22 GAMMA
CHANNELS
In addition to the V_COM outputs, the REFH and REFL OUT
outputs can also be used as fixed gamma references. The
output voltage will be set by the REFH and REFL input
voltages, respectively. Therefore, REFH OUT should be
used for the highest voltage gamma reference, and REFL
OUT for the lowest voltage gamma reference. A
22-channel solution can be created by using all 18 outputs,
the two V_COM outputs, and both REFH/L OUT outputs for
gamma references—see Figure 15. However, the REFH
and REFL OUT buffers were designed to only drive light
loads on the order of 5−10mA. Driving capacitive loads is
not recommended with these buffers. In addition, the
REFH and REFL buffers must not be allowed to saturate
from sourcing/sinking too much current from REFH OUT
or REFL OUT. Saturation of the REFH and REFL buffers
results in errors in the voltages of OUT1−18 and V_COM
OUT1−2. The BUF01900, which is anticipated to be
released in Q3 ’05, can be used to provide a
programmable V_COM output.
BUF20800
SBOS329D − JUNE 2005 − REVISED OCTOBER 2006
15V
2V−5.5V
14.8V
Digital
BUF20800
Analog
REFH
REFH OUT
14.8V
Source
Driver
V_{CO M} OUT1
GMA 1
V_{CO M} OUT2
GMA 2
OUT1
OUT2
GMA 3
GMA 4
18 Gamma Channels
SDA
SCL
Control IF
LD
A0
REFL
OUT17
GMA 19
OUT18
REFL OUT
0.2V
GMA 20
15V
0.2V
Figure 14. 20 Gamma Channel Solution − 2 V_COM
Channels Used as Additional Gamma Channels
15