OPA197: OPA197 overload recovery time VS propagation delay time

Hello Red,

Overload recovery time is the time it takes the OPA197 output to recover from being slammed against the positive or negative output swing rails. The input and gain conditions are set such that the amplifier circuit input voltage is VIN × G = Vs. In Figures 30 and 31 the input level appear to be about +2 V and -2 V, respectively. Since the gain is -10 V/V, the output in Fig 31 would attempt to swing to -20 V with the +2 V input, but would be limited by the +/-18 V supply to not quite -18 V. Similarly, in Fig 30 when the input is -2 V the output would be up against the output rail at a level near +18 V. Once the input level is returned to 0 V in each figure it takes a finite amount of time, typically 200 ns, for the output to recover and move back into the linear output operating region.

Since the OPA197 doesn't have the typical back-to-back input diodes that many op amps require for input protection, it can be more easily applied as a high voltage comparator. The datasheet states in Section 9.3 "The OPAx197 uses a unique input architecture to eliminate the need for input protection diodes, but still provides robust input protection under transient conditions." and "The OPA197 can tolerate a maximum differential swing (voltage between inverting and noninverting pins of the op amp) of up to 36 V, making the device suitable for use as a comparator or in applications with fast-ramping input signals such as multiplexed data-acquisition systems, as shown in Figure 53."

Figures 39 and 40, shows the propagation delay times of the OPA197 when applied as a comparator, as Michael suggested. Figure 40 should have a 5 V/div vertical scale like Fig. 39 so it is mislabeled also as Michael suggested. These Propagation Delay graphs are somewhat unique to the OPA19x family of op amps because they can be readily applied as a comparator and the information is provided for that use.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Red,

The OPA197 overload recovery time is simply the time it takes for the output to recovery from being in the saturated state to returning to the linear output. Note that there is a very specific gain setting as well for the Overload recovery time is typically 200ns, where VIN× G = VS.

 When operating as a comparator the propagation delay time has more time components to it, and the gain is now running open loop. The OPA197 output is slamming into each of the output rails so there is overload recovery time, the actual propagation time through the op amp, and delay due to slew rate limiting. The sum total is about 1us as indicated in the Figure 39 and 40  Propagation Delay graphs.

Regards, Thomas

Precision Amplifiers Applications Engineering