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OPA454 feedback capacitor

Dario Di Turi
Prodigy 120 points

Hi.

How to calculate the value of feedback capacitor Cf in the datasheet in figure 60 (External outputs transistors boost output current greater than 1A)?

Thank's

  • 0
    Guru 21975 points

    Dario,

    This may not be an entirely satisfying  answer but this capacitor value Cf is probably best determined by experimentation. The optimum value will depend on many factors including closed-loop gain (R1, R2), transistor selection, load characteristics (resistive/capacitive, etc.) and output current range.

    I suggest that you start with approximately 500pF. Use the response to a small input step voltage of 50mV, or so, to test the circuit with your actual operating conditions. Focus attention on the response at the lowest expected current levels. A response of greater than approximately 20% overshoot is tending toward instability and needs a higher capacitor value.

    Regards, Bruce.