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Big Gain from OPA548

Mitch Ridgeway
Expert 6635 points

Other Parts Discussed in Thread: OPA548

Hello,

I am using the OPA548 and am getting a very large gain. I am expecting a gain of 4, but I am getting a gain of 60 (with and without a load). I am supplying the chip with 18V. When I input 200mV, my output is 12V. I am attaching a schematic of my design. Do you know why my gain is so high?

Thanks,

Mitch Ridgeway

  • 0
    TI__Guru* 93105 points

    Hi Mitch,

    Your OPA548 application circuit is straightforward and doesn't hint at any reason why the gain would be 60 V/V, instead of the expected 4 V/V. Have you measured R19 and R18 to be sure they are the values you intended? Have you seen this gain descrepancy on more than one board?

    When you observe the OPA548 output with the 200 mV applied at the input, does the output waveform show any distortion or show any evidence of instability? Does this high gain occur at any particular frequency, or is consistent across the useable bandwidth?

    Regards, Thomas

    PA - Linear Applications Engineering