Datasheet

2PSec/DIV
(5V/DIV)
(2V/DIV)
V
SW
V
COM
+
-
V
SW
R
L1
10:
-6.5V
V
COM
+6.5V
I
OUT
C
1
10nF
C
2
10nF
C
3
10nF
C
4
10nF
R
L3
10:
R
S
10:
R
L2
10:
V
COM
LOAD
0V
5V
R
F2
300:
R
F1
3k:
LM6588
www.ti.com SNOSA77D –MAY 2003–REVISED MARCH 2013
Figure 29. V
COM
Driver Test Circuit
Figure 29 is a common test circuit used for measuring V
COM
driver response time. The RC network of R
L1
to R
L3
and C
1
to C
4
models the distributed RC load of a V
COM
line. This RC network is a gross simplification of what the
actual impedance is on a TFT panel. However, it does provide a useful test for measuring the op amp’s transient
response when driving a large capacitive load. A low impedance MOSFET driver applies a 5V square wave to
V
SW
, generating large current pulses in the RC network. Scope photos from this circuit are shown in Figure 30
and Figure 31. Figure 30 shows the test circuit generates positive and negative voltage spikes with an amplitude
of ±3.2V at the V
COM
node, and both transients settle-out in approximately 2μs. As mentioned before, the speed
at which these transients settle-out is a function of the op amp’s peak output current. The I
OUT
trace in Figure 31
shows that the LM6588 can sink and source peak currents of −200mA and 200mA. This ability to supply large
values of output current makes the LM6588 extremely well suited for V
COM
Driver applications.
Figure 30. V
SW
and V
COM
Waveforms from V
COM
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