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TPS78001 / Operation with prebiased condition

S.Satoshi
Guru 21675 points
Other Parts Discussed in Thread: TPS780

Hi,

Please let me know the operation of TPS78001 with prebiased condition and concern. I'm assuming the 2.5V prebias will be applied to Vout via 10kohm after power up. I understand that the output voltage can not be regulated correctly and the Vout will be higher than normal voltage.

  • Do you think this will be cause of damage or unstable operation?
  • Do you think this will be cause of false operation of active pull-down circuit?

Your comment will be appreciated.

Best Regards,

Sonoki / Japan Disty

  • 0
    TI__Guru 55940 points
    Sonoki-san,

    As with many LDOs that do not have a dedicated reverse voltage circuit, TPS780 is not intended for the output to exceed the input. This condition will allow for reverse current to flow through the body diode of the pass element. The body diode does not limit the current; therefore, we recommend using external circuitry (ie diode in parallel with the LDO) to create a robust path for the reverse current.

    The active discharge function only operates when Vin is greater than 2.2V per sectino 7.3.3 of the datasheet. If Vin is greater than 2.2V and EN is logic low, the pulldown circuitry will attempt to pulldown the output voltage through a 10k resistor.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Guru 21675 points

    Hi Ryan,

    Thank you for your comment. I understand that the active pull-down circuit will not be activated at EN=Low regardless biased condition to Vout.

    And also I know that we need to care about reverse current but at this time input voltage is higher than biased voltage, so I believe there is no risk of it.

    Best Regards,

    Sonoki

  • 0 in reply to S.Satoshi
    Guru 21675 points

    Sorry, there is typo. it should be "EN=High"...

    I understand that the active pull-down circuit will not be activated at EN=High regardless biased condition to Vout.