OP176 Datasheet, PDF (10/21 Pages) Analog Devices – Bipolar/JFET, Audio Operational Amplifier

OP176
Output Voltage Phase Reversal
Since the OP176’s input stage combines bipolar transistors for
low noise and p-channel JFETs for high speed performance, the
output voltage of the OP176 may exhibit phase reversal if either
of its inputs exceeds the specified negative common-mode input
voltage. This might occur in some applications where a trans-
ducer, or a system, fault might apply very large voltages upon
the inputs of the OP176. Even though the input voltage range
of the OP176 is ± 10.5 V, an input voltage of approximately
–13.5 V will cause output voltage phase reversal. In inverting
amplifier configurations, the OP176’s internal 7.5 V clamping
diodes will prevent phase reversal; however, they will not
prevent this effect from occurring in noninverting applications.
For these applications, the fix is a 3.92 kΩ resistor in series
with the noninverting input of the device and is illustrated in
Figure 31.
R _FB*
V _IN
2 _OP176 ⁶
ΩR_S ³
3.92kΩ
V _OUT
ΩR_L
2kΩ
*R_FB IS OPTIONAL
Figure 31. Output Voltage Phase Reversal Fix
Overdrive Recovery
The overdrive recovery time of an operational amplifier is the
time required for the output voltage to recover to a rated output
level from a saturated condition. This recovery time is impor-
tant in applications where the amplifier must recover quickly
after a large abnormal transient event. The circuit shown in
Figure 32 was used to evaluate the OP176’s overload recovery
time. The OP176 takes approximately 1 µs to recover to V_OUT =
+10 V and approximately 900 ns to recover to V_OUT = –10 V.
R1
Ω1kΩ
R2
Ω10kΩ
V _IN
4Vp-p
@100Hz
2
6
3 ^OP176
R_S
909Ω
V _OUT
R_L
Ω2.43kΩ
Figure 32. Overload Recovery Time Test Circuit
High Speed Operation
As with most high speed amplifiers, care should be taken with
supply decoupling, lead dress, and component placement.
Recommended circuit configurations for inverting and
noninverting applications are shown in Figure 33 and Figure 34.
+15V
10µF
+
0.1µF
2
7
6
V_OUT
V_IN
OP176
3
4
R_L
2kΩ
0.1µF
10µF
–15V
Figure 33. Unity Gain Follower
+15V
10µF
+
0.1µF
4.99kΩ
V_IN
2.49kΩ
10pF
4.99kΩ
2
7
6
OP176
3
4
V_OUT
2kΩ
0.1µF
10µF
+
–15V
Figure 34. Unity Gain Inverter
In inverting and noninverting applications, the feedback
resistance forms a pole with the source resistance and capaci-
tance (R_S and C_S) and the OP176’s input capacitance (C_IN), as
shown in Figure 35. With R_S and R_F in the kΩ range, this pole
can create excess phase shift and even oscillation. A small
capacitor, C_FB, in parallel with R_FB eliminates this problem. By
setting R_S (C_S + C_IN) = R_FB C_FB, the effect of the feedback pole is
completely removed.
C_FB
R_FB
R_S
C_S
C_IN
V_OUT
Figure 35. Compensating the Feedback Pole
–10–
REV. 0