OP1177/OP2177/OP4177
R2
100kΩ
Figure 56 is a scope shot of the output of the OPx177 in response
to a 400 mV pulse. The load capacitance is 2 nF. The circuit is
configured in positive unity gain, the worst-case condition for
stability.
V+
R1
1kΩ
7
2
3
V
OUT
6
+
–
200mV
OP1177
10kΩ
As shown in Figure 58, placing an R-C network parallel to the
load capacitance (CL) allows the amplifier to drive higher values
of CL without causing oscillation or excessive overshoot.
4
V–
Figure 54. Test Circuit for Overload Recovery Time
There is no ringing, and overshoot is reduced from 27% to 5%
using the snubber network.
Figure 18 shows the positive overload recovery time of the
OP1177. The output recovers in less than 4 ꢀs after being
overdriven by more than 100%.
Optimum values for RS and CS are tabulated in Table 5 for several
capacitive loads, up to 200 nF. Values for other capacitive loads can
be determined experimentally.
The negative overload recovery of the OP1177 is 1.4 ꢀs, as seen
in Figure 19.
Table 5. Optimum Values for Capacitive Loads
CL
RS
CS
THD + NOISE
10 nF
50 nF
200 nF
20 Ω
30 Ω
200 Ω
0.33 ꢀF
6.8 nF
0.47 ꢀF
The OPx177 has very low total harmonic distortion. This indicates
excellent gain linearity and makes the OPx177 a great choice for
high closed-loop gain precision circuits.
Figure 55 shows that the OPx177 has approximately 0.00025%
distortion in unity gain, the worst-case configuration for distortion.
V
R
C
= ±5V
= 10kΩ
= 2nF
SY
L
L
0.1
V
= ±15V
SY
R
= 10kΩ
L
BW = 22kHz
0.01
0.001
0
GND
TIME (10µs/DIV)
0.0001
Figure 56. Capacitive Load Drive Without Snubber
100
1k
20
6k
FREQUENCY (Hz)
Figure 55. THD + N vs. Frequency
V
= ±5V
= 10kΩ
= 200Ω
= 2nF
SY
CAPACITIVE LOAD DRIVE
R
R
C
C
L
S
L
S
OPx177 is inherently stable at all gains and capable of driving
large capacitive loads without oscillation. With no external
compensation, the OPx177 safely drives capacitive loads up to
1000 pF in any configuration. As with virtually any amplifier,
driving larger capacitive loads in unity gain requires additional
circuitry to assure stability.
= 0.47µF
GND
In this case, a snubber network is used to prevent oscillation
and reduce the amount of overshoot. A significant advantage of
this method is that it does not reduce the output swing because
the Resistor RS is not inside the feedback loop.
TIME (10µs/DIV)
Figure 57. Capacitive Load Drive with Snubber
Rev. E | Page 16 of 24
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