OP27A, OP27C

LOW-NOISE HIGH-SPEED PRECISION OPERATIONAL-AMPLIFIER

SLOS100E − FEBRUARY 1989 − REVISED FEBRUARY 2010

17

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

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 k

Ω, R2 = 200 Ω, and

AVD = 100.

15 V

+

−

−15 V

R1

50 k

Ω

R2

100

Ω

R3

50 k

Ω

VO = 1000 VIO

2

3

6

7

4

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 Rf ≤ 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.

+

−

Rf

Output

2.8 V/

μs

OP27

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 Rf ≥ 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

Rf > 2 kΩ, a pole is created with Rf 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 Rf eliminates this problem.