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TPS546C20A: Can external power be applied to BP3.

Ronnie Hughes
Expert 3080 points
Part Number: TPS546C20A
Other Parts Discussed in Thread: TPS546D24A

Customer needs to change output voltage via PMBus interface before Vin is available.  Can power be applied to BP3 pin to power up the regulator when Vin is not present?  Any potential to damage the internal 3.3V LDO by doing this?  Will there be an leakage back to Vin from BP3 being powered?

Thanks,

  • 0
    TI__Mastermind 48200 points

     

    The TPS546C20A does not support doing this.

    1) BP3 does not support back-biasing.

    The BP3 LDO includes a parasitic BP3 to AVIN diode that would attempt to charge AVIN through BP3 if BP3 is greater than AVIN.

    2) The TPS546C20A Under Voltage Lock-out requires AVIN, BP6 and BP3 to all be powered prior to enabling PMBus communication.

    To program the TPS546C20A before PVIN is applied, they would need to separate AVIN and PVIN and power AVIN above 4.2V to enable the PMBus of the TPS546C20A.  However, PVIN is powered, the high-side current limit requires AVIN = PVIN while holding AVIN less than PVIN will disable the high-side current limit and short circuit protection.

    The TPS546D24A, a newer, higher current 4x stackable average current mode control part with PMBus is designed to allow PMBus programming by powering the IC from a diode connected 3.3V supply.  An external 3.3V supply can be diode-ORed into AVIN to power VDD5 and BP1V5 with no power applied to PVIN.

    If a 4.0V - 5.25V supply is available to power VDD5 separately from AVIN, AVIN can be powered from 3.3V, VDD5 from 5V and PVIN from any voltage within its range.  The TPS546D24A senses the high-side FET current from PVIN to SW rather than AVIN to SW, so there is no requirement that AVIN be equal to PVIN.