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TPS51200: REFOUT overshoot at power down

Kazuki Itoh
Genius 10730 points
Part Number: TPS51200

Hello team,

Could you please help us to address REFOUT overshoot issue at power down?

It looks like it happens when VIN powers down before VLDOIN powers down.

Please find internal link here for the waveform and schematic. (Please connect to VPN for download)

Best regards,

Itoh

  • 0
    TI__Expert 5965 points

    Hi Itoh-san,

    When EN goes low (in this case, EN is the same as 3.3V), TPS51200 discharges REFOUT by an internal FET. If VIN goes low as well, the discharge FET loses driver voltage and will be off. In this case, if REFIN is still high, REFOUT will try to follow REFIN and will rise up again. I think this is what happened in this case. 

    Regards,

    Weidong

  • 0 in reply to Weidong Zhu
    TI__Genius 10730 points

    Hello Weidong-san,

    It makes sense that the power sequence turns the discharge FET on and off.

    However, I wonder why the peak of REFOUT overshoot goes over 1V because REFIN is 0.675V in this case.

     Is the internal unity gain buffer at REFIN pin biased by the VLDOIN (1.35V)?

    What do you recommend to avoid this issue?

    Do you recommend to enable TPS51200 from the separate signal? 

    Regards,

    Itoh

  • 0 in reply to Kazuki Itoh
    TI__Expert 5965 points

    Hi Itoh-san,

    I'll need to check with design team on how the unity gain buffer is connected and why the overshoot can go beyond 0.675V. Will keep you updated.

    To avoid this issue, I think you can recommend customer to power down VLDOIN before removing 3.3V supply to TPS51200. I think this is usually the case in the system design.

    Regards,

    Weidong

  • 0 in reply to Weidong Zhu
    TI__Expert 5965 points

    Hi Itoh-san,

    We were not able to duplicate this from our side. We suspect there is a leakage from VDDQ to VTTREF on the load side. That's why this issue goes away when VLDOIN is powered down at the same time with 3.3V.

    Regards,

    Weidong