OP297

Rev. F | Page 9 of 16

APPLICATIONS INFORMATION

5µs

20mV

10

0%

100

90

Extremely low bias current over a wide temperature range

makes the OP297 attractive for use in sample-and-hold

amplifiers, peak detectors, and log amplifiers that must operate

over a wide temperature range. Balancing input resistances is

degraded only minimally by high source resistance, even

when unbalanced.

The input pins of the OP297 are protected against large differen-

tial voltage by back-to-back diodes and current-limiting resistors.

Common-mode voltages at the inputs are not restricted and can

vary over the full range of the supply voltages used.

Figure 28. Large Signal Transient Response (A

= 1)

The OP297 requires very little operating headroom about the

supply rails and is specified for operation with supplies as low as

2 V. Typically, the common-mode range extends to within 1 V

of either rail. The output typically swings to within 1 V of the

rails when using a 10 kΩ load.

VCL

UNITY-GAIN FOLLOWER

–

+

1/2

OP297

INVERTING AMPLIFIER

–

+

1/2

OP297

MINI-DIP

BOTTOM VIEW

8

B

1

A

NONINVERTING AMPLIFIER

–

+

1/2

OP297

AC PERFORMANCE

The ac characteristics of the OP297 are highly stable over its full

operating temperature range. Unity gain small signal response is

shown in Figure 26. Extremely tolerant of capacitive loading on

the output, the OP297 displays excellent response with 1000 pF

loads (see Figure 27).

10

100

90

0%

10

20mV

5µs

Figure 29. Guard Ring Layout and Considerations

GUARDING AND SHIELDING

To maintain the extremely high input impedances of the

OP297, care is taken in circuit board layout and manufacturing.

Board surfaces must be kept scrupulously clean and free of

moisture. Conformal coating is recommended to provide a

humidity barrier. Even a clean PC board can have 100 pA of

leakage currents between adjacent traces, so guard rings should

be used around the inputs. Guard traces operate at a voltage

close to that on the inputs, as shown in

= 1)

VCL

5µs

20mV

10

0%

100

90

Figure 29, to minimize

leakage currents. In noninverting applications, the guard ring

should be connected to the common-mode voltage at the

inverting input. In inverting applications, both inputs remain at

ground, so the guard trace should be grounded. Guard traces

should be placed on both sides of the circuit board.

= 1)

VCL