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OPA170 / reverse rush current from output capacitor

Toshiyuki
Mastermind 7075 points

Other Parts Discussed in Thread: OPA170

Hi,

We are able to use OPA170 under the following conditions.

Vin=36V, Vout= up to 35V, Io=3.5mA max

When Vin is toggled 36V to 0V, do a reverse rush current problem occur from output capacitor?

Best Regards,

Kato

  • 0
    TI__Guru 64885 points

    Hello,

    During power-down if a condition where the output voltage is greater than the supply voltage by ~0.3V then the output protection structures will turn on and conduct current.  If the current through the protection device is greater than 10mA for any length of time then damage will likely occur to the amplifier output stage. 

    The current that the output stage must sink to discharge the output capacitor is directly related to the value of the output capacitance and the rate of change of the supply voltage (i=C*dV/dt).  If a series resistor is placed between the op amp output and the output capacitor this will also affect the current the op amp must discharge.

    Please post a scope shot of the power-supply ramp down waveforms and we'll analyze the situation further.