OP27GU Datasheet, PDF (17/22 Pages) Texas Instruments – LOW-NOISE HIGH-SPEED PRECISION OPERATIONAL AMPLIFIERS

OP27A, OP27C
LOW-NOISE HIGH-SPEED PRECISION OPERATIONAL-AMPLIFIER
SLOS100E − FEBRUARY 1989 − REVISED FEBRUARY 2010
APPLICATION INFORMATION
offset voltage and drift (continued)
The circuit shown in Figure 30 measures offset voltage. This circuit can also be used as the burn-in configuration
for the OP27 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
V_O = 1000 V_IO
NOTE A: Resistors must have low thermoelectric potential.
Figure 30. 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 31.
R_f
−
+ _OP27
Output
2.8 V/μs
Figure 31. 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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