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TPS23756: PoE Priority Circuit Using Controlled Adapter High-Side Switch Vout drop issue

Sam Shyu36
Intellectual 735 points
Part Number: TPS23756
Other Parts Discussed in Thread: PMP20859

Dear Sir,

We use application note ( slva306a ) to do PoE Priority Circuit Using Controlled Adapter High-Side Switch (as below circuit). But Vout will drop when Adapter supply first then PSE plug in (as below waveform ; CH1: Vout; CH4 VDD1). Do you have any suggestion for Vout drop issue?

Best Regards,

Sam Shyu

  • 0
    TI__Genius 9230 points

    Hi Sam,

    This circuit is not intended for smooth transition from adapter to PoE input. The PoE input will take priority, but the adapter input will turn off at Vdd-Vss = ~30V before the PoE input exceeds the rising UVLO (36V) to turn on the hotswap FET.

    If the customer needs smooth transition between adapter & PoE input, I recommend using the example in section 3.6 of SLVA306A or modifying our hitless transition design, PMP20859, to use a single channel instead of 2.

    Thanks,
    Tom Amlee
    PoE PD Apps Engineer

  • 0 in reply to Thomas Amlee
    Intellectual 735 points

    Hi Tom,

    Thanks!

    Best Regards,

    Sam