OPA196: Unity gain stable

ttd

Mastermind 8150 points

Part Number: OPA196
Other Parts Discussed in Thread: OPA197, OPA228, TINA-TI, OPA202

Dear Technical Support Team,

Are OPA196 and OPA197 unity gain stable?

Datasheets described unity gain bandwidth.

Do you have selection guide for unity gain stable?

Best Regards,

ttd

over 2 years ago

+1 Clemens Ladisch over 2 years ago

Guru 288510 points

The OPA196/7 are unity-gain stable. Decompensated opamps (like the OPA228) are marked as such in the datasheet and in the search function (it's a checkbox in "Features"), and specify the minimum closed-loop gain in the electrical characteristics.

+1 Marek Lis over 2 years ago

TI__Guru 64680 points

TTD,

OPA196 and OPA197 are unity-gain stable but when driving directly (with no Riso resistor) their capacitive load is limited. Thus, for example, OPA197 graph shows that driving 300pF load the small-signal overshoot is 25% (the maximum recommended to assure stability over process variation) - see below.

Thus, for example, you cannot drive directly 1uF load - see below.

However, adding just 5 ohm Riso resistor makes the circuit stable - see below.

The above solution works well if there is no resistive load, which otherwise would cause a gain error - see below.

Thus, to solve the gain error problem the solution is to use dual-feedback compensation as shown below.

To confirm stable operation you may also run AC stability simulation showing 83 degrees phase margin whereas the minimum recommended is 45 degrees - see below.