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OPA858: Overdrive recovery clarification

Dharani Jade
Prodigy 65 points
Part Number: OPA858
Other Parts Discussed in Thread: OPA857

Tool/software:

We're trying to test an APD+ OPA858 circuit and we need to estimate the overload recovery of the module, i.e., how long after a large input optical pulse is incident, can we accurately measure a normal pulse. The OPA858 completely clamps the output at the high pulse power we are measuring at (based on our specifications), so its hard to see when it 'recovers'. Can someone explain what 2x output overdrive means and what is the measured OPA858 recovery (200ns is what is mentioned but im confused with the way its described)? Would also be helpful to know how the internal clamping works to understand the recovery better.

Thanks in advance!

Kind Regards,

Dharani Jade

  • 0
    TI__Mastermind 28915 points

    Hello Dharani,

      Thanks for reaching out to us! 

      When the specification mentions 2x overdrive for test condition, this means that the input voltage or gain to the amplifier is set where it would give an output voltage 2 times over  the output voltage high value at the supply configuration. From snippet below of the output voltage range of the amplifier, at 5V this is 4.1V high or at 2.5V this will be 1.6V high. 2x will be at around 3.2V. At this overdrive voltage, it will clamp at the specified output voltage range of the amplifier. Once, the overdriven is removed, as in the input voltage or gain is altered where the amplifier output voltage should be within the typical output voltage range, then it will take typically 200ns for the time it takes for the amplifier to return to normal operation within 0.1% of the desired output signal. 

       The Figure 6-22 shows an overdriven response driven at 2x, ideally this would go up all the way to 2.5 + ESD 0.1V at +/-2.5V supply config. However, amplifier clamps at 1.6V as shown in the figure. It would have been useful to shown the overdrive recovery response like we do in OPA857 as shown below:

       I can check if we have these plots to share for OPA858.

      During your testing are you seeing a high overdrive recovery time, or is the output still in overdrive/clamped state?

    Best Regards,
    Sima