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TPS65988: VBUS and PP_HV capacitance

Daniels Kurgs
Prodigy 180 points
Part Number: TPS65988

Hello TI Team,

we are planning to use the TPS65988 as a dedicated power source for both ports and are unsure about the capacitance on our device. Our device would be entirely self-powered.

Both USB 3.2 spec (Section 11.4.4.1) and USB 2.0 spec (7.2.4.1) expect  at least 120uF of low ESR capacitance on the VBUS pins on downstream facing ports.

The datasheet, however, has absolute max limits of 12uF on VBUS (Table 29).

1. Should we understand that the bulk capacitance needs to be placed on the PP_HV pins in source only configuration? This might expose the internal power path switches to higher inrush currents etc.

2. Or - can the VBUS capacitance limit be ignored if the product is configured in source only mode?

Thank you!

Kind regards,

Daniels

  • 0
    TI__Mastermind 32661 points

    Daniels,

    1.  The only time that you need 120uF of capacitance is if you plan to support fast role swap in a DRP.  Because your system is described as a DFP, you only need to have 10uF of capacitance.

    2.  You cannot ignore the VBUS capacitance limit.  It is necessary to meet the specified operation of the device.

    Regards,

    Chuck