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OPA355-Q1: How to coodinate phase margin of high speed amplifier

Takao Yamamoto5
Expert 1690 points
Part Number: OPA355-Q1
Other Parts Discussed in Thread: TINA-TI,

Dear all,

My customer concern oscillation of this high speed amplifier with high load capacitance(around 1nF).

Could you teach us the appropriate way to coodinate phase margin?

Simulation by TINA-TI? Test by FRA? or Test by oscilloscope with changing capacitance load and resistor?

We think that high speed amplifier can oscillate easier than general purpose amplifiers.

So, we would like to know the right way to coodinate phase margin.

Best regards,

  • 0
    Guru 140200 points
    Hi Takao,

    first, you should carry out a phase stability analysis as discussed in the TI's stability videos:

    training.ti.com/ti-precision-labs-op-amps

    Then, you can check the result with the scope.

    Which method is best to cure the instability heavily depends on your circuit. You might want to show us a schematic?

    Kai
  • 0
    TI__Genius 15975 points
    Hi Takao-san,

    For high load capacitance drive, usually the higher frequency inductance in the device output needs to be isolated from the capacitive load. This isolations is usually done by the inclusion of a series resistor.

    I would recommend looking at Figure 35 in the OPA355-Q1 datasheet, which shows a schematic of 100-ohm series isolation resistor while driving a 1nF capacitive load.

    As Kai mentioned, the phase stability analysis can be found in the TI's stability videos training: training.ti.com/ti-precision-labs-op-amps

    It would be helpful if you can forward the schematic for further support.

    Best Regards,
    Rohit