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TPS54622: negative voltage on PH during start up. TPS54622

Given Ding
Expert 7325 points
Part Number: TPS54622

Hi Team,

I have a question on TPS54622.
During startup, there is negative voltage on PH but I'm not sure about the reason. It seems like body diode of LS has current . But  In startup, it should be DCM mode to achieve pre-bias startup. So want to check o this.

  • 0
    TI__Guru**** 191445 points

    Given,

    For TPS54622 the low side FET cannot sink any current until SS/TR reaches 1.4 V.  So during the on time, the inductor current ramps up and PH is at VIN.  During the off time the inductor current ramps down, and PH is negative equal to IL times RDSon.  when teh inducto current reaches zero, the low side FET turns off, so the PH waveform looks like DCM.