BUF05704 Datasheet, PDF (14/25 Pages) Burr-Brown (TI) – 18 - V SUPPLY MULTI - CHANNER GAMMA CORRECTION BUFFER

BUF05704, BUF06704
BUF07704, BUF11704
SBOS277E − JUNE 2004 − REVISED DECEMBER 2004
ESD RATINGS
The BUFxx704 has excellent ESD performance: 8 kV
HBM; 2 kV CDM; and 300 V MM. These ESD ratings
allow for increased manufacturability, fewer production
failures, and higher reliability.
INPUT VOLTAGE RANGE GAMMA BUFFERS
Figure 22 shows a typical gamma correction curve with
10 gamma correction reference points (GMA1 through
GMA10). As can be seen from this curve, the voltage
requirements for each buffer vary greatly. The swing
capability of the input stages of the various buffers is
carefully matched to the application. Using the example
of the BUF11704 with 10 gamma correction channels,
buffers 1 to 5 have input stages that include V_DD, but will
only swing within 1 V to GND. Buffers 1 through 5 have
only a single NMOS input stage. Buffers 6 through 10
have only a single PMOS input stage. The input range
of the PMOS input stage includes GND.
VDD1
GMA1
GMA2
GMA3
GMA4
GMA5
GMA6
GMA7
GMA8
GMA9
GMA10
VSS10
10
20
30
40
Input Data (Hex)
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this architecture, the correct buffer needs to be
connected to the correct gamma correction voltage.
Connect buffer 1 to the gamma voltage closest to V_DD,
and buffers 2 through 5 to the following voltages. Buffer
10 should be connected to the gamma correction
voltage closest to GND (or the negative rail), and
buffers 9 through 6 to the following higher voltages.
COMMON BUFFER (V_COM)
The common buffer output of the BUFxx704 has a
greater output drive capability than the gamma buffers
to meet the heavier current demands of driving the
common node of the LCD panel. The common buffer
output was also designed to drive heavier capacitive
loads. Excellent output swing is possible with high
currents ( > 100 mA), as shown in Figure 23.
OUTPUT VOLTAGE vs OUTPUT CURRENT
18
17
16
15
14
13 ^VDD ^{= 18 V}
12 T_A = 25_ C
11
7
6
5
4
3
2
1
0
0 25 50 75 100 125 150 175 200 225 250
Output Current − mA
Figure 23. V_COM Output Drive Capability
Figure 22. Gamma Correction Curve
OUTPUT VOLTAGE SWING GAMMA BUFFERS
The output stages have been designed to match the
characteristic of the input stage. Once again, using the
example of the BUF11704, this means that the output
stage of buffers 1 to 5 swing very close to V_DD, typically
V_CC − 100 mV at 10 mA; its ability to swing to GND is
limited. Buffers 6 through 10 swing closer to GND than
V_DD. Buffers 6 to 10 are designed to swing very close
to GND; typically, GND + 100 mV at a 10 mA load
current. See the Typical Characteristics for more
details. This approach significantly reduces the silicon
area and cost of the whole solution. However, due to
14
CAPACITIVE LOAD DRIVE
The BUFxx704 has been designed to be able to
sink/source large dc currents. Its output stage has been
designed to deliver output current transients with little
disturbance of the output voltage. However, there are
times when very fast current pulses are required.
Therefore, in LCD source driver buffer applications, it is
quite normal for capacitors to be placed at the outputs
of the reference buffers. These capacitors improve the
transient load regulation and will typically vary from
100 pF and more. The BUFxx704 gamma buffers were
designed to drive capacitances in excess of 100 pF. The
output is able to swing within 150 mV of the rails on 10
mA of output current, see Figure 24.