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TPS610333: When disabled, is output high-impedance?

Ev Zin
Prodigy 50 points
Part Number: TPS610333

Hello

I want to use the TPS610333 as a backup power system to temporarily power a board using a supercap as a source. The TPS610333 will be connected to the system 5V rail in parallel to another, main switching regulator. During normal operation, the TPS610333 is disabled. I will be controlling the TPS610333 enable pin with a voltage monitor to detect when main power fails, so I am hoping that the output of the TPS610333 is high-impedance when disabled. Is this case? Or more generally, is it ok for the TPS610333 to see 5V at the output when it is not the one providing the power?

Thanks!

  • 0
    TI__Expert 8515 points

    Hi Ev,

    When disabled, the output is disconnected with input, so it is high-impedance, and also no problem with 5V at the output when disabled.

    Regards,

    Nathan

  • 0 in reply to Nathan Ding
    Prodigy 50 points

    Thank you for the response. One follow up question, if there is a collapsing 5V at the output when the TPS610333 turns on (meaning the output may not be completely dead to 0V when the TPS610333 enables), will that be a problem? I am trying to eliminate the need for a load switch or series schottky diode protecting the VOUT from any reverse current flow from the 5V rail.

  • 0 in reply to Ev Zin
    TI__Expert 8515 points

    Hi Ev,

    When enabled, with PFM mode, if setting the pre-bias voltage a little higher than (at least 1% higher) the target output voltage of the IC, it is no problem. For example, the output voltage of TPS610333 is 5V, and the voltage at output when enabled is 5.1V, it is no problem, otherwise the supercap may be discharged even when the pre-bias voltage is present.

    With FPWM, we don’t recommend to do this, there may be an inverse current going through the IC.

    Regards,

    Nathan

  • 0 in reply to Nathan Ding
    Prodigy 50 points

    The output of the TPS610333 would not ever see more than 5V on the output. What i meant was as the main switching regulator shuts down, the 5V on the rail would be falling as the TPS610333 becomes active. So the TPS610333 would be seeing a non-zero voltage at the output (but still 5V or less) when it starts up. I just was wondering if there would be an issue of a non-zero, but 5V or less, voltage at the output of the TPS610333 when it starts up would be a problem. Based on your answer, I don't think it would be...?

    I was planning on using FPWM mode but i guess i could use the PFM if needed. The super cap would be isolated from the input of the TPS610333 with a load switch and not enabled until the main power went down. The load switch isolating the super cap and the enable on the TPS610333 would activate at the same time via a signal from a voltage monitor. Where i was trying to avoid putting a load switch or diode was between the TPS610333 output and the 5V rail.

  • +1 in reply to Ev Zin
    TI__Expert 8515 points

    Hi Ev,

    Sorry for misunderstanding your question.

    It is no problem for TPS610333 to startup with a non-zero voltage at VOUT, no matter it is PFM or FPWM.

    TPS610333 can support startup with pre-bias voltage at VOUT.

    Regards,

    Nathan