OP27A Datasheet, PDF (19/21 Pages) Texas Instruments – LOW-NOISE HIGH-SPEED PRECISION OPERATIONAL AMPLIFIERS

OP27A, OP27C, OP27E, OP27G
OP37A, OP37C, OP37E, OP37G
LOW-NOISE HIGH-SPEED PRECISION OPERATIONAL AMPLIFIERS
SLOS100B – FEBRUARY 1989 – REVISED AUGUST 1994
APPLICATION INFORMATION
offset voltage and drift (continued)
The circuit shown in Figure 38 measures offset voltage. This circuit can also be used as the burn-in configuration
for the OP27 and OP37 with the supply voltage increased to 20 V, R1 = R3 = 10 kΩ, R2 = 200 Ω, and
A_VD = 100.
R1
50 kΩ
R2
100 Ω
R3
50 kΩ
15 V
2– ⁷
6
3
+
4
–15 V
VO = 1000 VIO
NOTE A: Resistors must have low thermoelectric potential.
Figure 38. Test Circuit for Offset Voltage and Offset Voltage
Temperature Coefficient
unity gain buffer applications
The resulting output waveform, when R_f ≤ 100 Ω and the input is driven with a fast large-signal pulse (> 1 V),
is shown in the pulsed-operation diagram in Figure 39.
Rf
–
+ _OP27
Output
2.8 V/µs
Figure 39. Pulsed Operation
During the initial (fast-feedthrough-like) portion of the output waveform, the input protection diodes effectively
short the output to the input, and a current, limited only by the output short-circuit protection, is drawn by the
signal generator. When R_f ≥ 500 Ω, the output is capable of handling the current requirements (load
current ≤ 20 mA at 10 V), the amplifier stays in its active mode, and a smooth transition occurs. When
R_f > 2 kΩ, a pole is created with R_f and the amplifier’s input capacitance, creating additional phase shift and
reducing the phase margin. A small capacitor (20 pF to 50 pF) in parallel with R_f eliminates this problem.
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