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TPS65988: Time required for source switch from VIN_3.3V to Vbus

Max Guan
Intellectual 1350 points
Part Number: TPS65988

Hi team,

If Vin_3.3Vdrops due to some kinds of reason/protection and PD have to switched to be powered from Vbus, how much time it will cost for PD to be powered from Vbus? Is there a reference time range for that?

Customer reports a PD re-negotiation and see Vbus drop to around 5V and return to 20V about 2s after VIN_3.3V drops. ( Notebook connected to Type-C adapter and Notebook 3.3V rail cutoff)

Thanks.

  • 0
    TI__Mastermind 36756 points

    Hi Max,

    When VIN_3V3 is initially present during bootup (device is not in dead battery mode) then VIN_3V3 is removed and falls below 2.85 V. In this case, a hard reset of the TPS6598x is initiated by device firmware, prompting a reboot. Once a specified time interval is passed without a valid external VIN_3V3 supply, the device firmware initiates a hard reset of the TPS65988. After VBUS transitions to VSAFE0V, a new PD contract is negotiated and TPS65988 reboots in dead battery mode.

    If this answers your question, PLEASE select This resolved my issue

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    TI__Intellectual 1350 points

    Thanks Eric,

    So you mean there will be a reboot of FW if Vin_3.3V is cutoff and PD transmits to be powered from Vbus, and this will also lead to negotiation again, right?

    And you mentioned there is a specified time interval, is this defined in spec and have some values?

    Also checked from customer, it's an OVP test on 3.3V rail with adapter connected and 20V on Vbus. And I asked for their waveform capture of this process. CH1 is Vbus and CH4 is gate control signal for external switch. So it seems the external switch is turned off after Vin_3.3V drop below 2.85V as you mentioned. And is there any problem on waveform from your point of view?

    Thanks.

    Max

  • 0 in reply to Max Guan
    TI__Mastermind 36756 points
    Hi Max,

    Your scope shot looks good. The PD controller is behaving as expected.

    Thanks,
    Eric