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TPS7A4101: Should we take any countermeasures against reverse voltage?

Shinsuke Tanaka
Intellectual 520 points
Part Number: TPS7A4101

Dear Sirs or Madams,

If my understanding is correct, generally speaking the voltage on OUT pin of LDO should NOT exceed that on IN pin 

in order to avoid the reverse current from OUT pin to IN pin. 

But on our prototype board, the voltage on OUT pin becomes about 0.8V higher than that on IN pin

which I refer to as reverse voltage here, only during powering down of IN pin side.

Currently we are NOT sure on what paths the electrical charges on OUT pin side are discharged,

so we are NOT sure if the reverse voltage mentioned above actually causes reverse current from OUT pin to IN pin.

On this condition, should we take any countermeasures to avoid the reverse voltage?

Best regards,

Shinsuke Tanaka

Schottky
  • 0
    Guru 140200 points
    Hi Shinsuke,

    datasheet says that only a differential output to input voltage of 0.3V is allowed. More can kill the regulator. So, I would think about connecting a protection diode from output to input.

    Kai
  • 0 in reply to kai klaas69
    Intellectual 520 points
    Dear Kai-san,

    I appreciate your rapid response so much.
    I understand that reverse voltage at powering down which we are now experiencing should be avoided.
    I know that insertion of a diode between IN pin and OUT pin is an effective countermeasure, but our prototype board has limited space
    and adding one more diode is not necessarily preferable.
    So, if you have any other ideas to avoid reverse voltage, could you please let me know it?
    For example, I now think we should try to decrease the impedance between OUT pin and GND in order to accelerate the discharge
    from OUT pin side by adding pull down resistors etc.
    What do you think of this idea?

    Best regards,
    Shinsuke Tanaka
  • 0 in reply to Shinsuke Tanaka
    Guru 140200 points
    Hi Shinsuke,

    yes, decreasing the impedance between the output pin and GND can help. Depends a bit on your circuit.

    Kai
  • 0 in reply to kai klaas69
    Intellectual 520 points
    Dear Kai-san,

    I appreciate your rapid response.
    We'll try this countermeasure. I don't have further questions.

    Best regards,
    Shinsuke Tanaka