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[FAQ] TPS2373: Wiring of VC_IN and VC_OUT when no transfromer Aux Bias supply present

Prodigy 20 points

Replies: 1

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Part Number: TPS2373

Hi, 

I'm designing a .bt PoE 5-port switch with an ideal rectifier bridge. 

I want to use the PG pin, with a 10k ohm pull-up to 3.3V (one of the power supply outputs). It will trigger the ideal rectifier to transition to "ideal" state, and it will trigger my PSE chip to begin operation (TPS23880). 

This circuit does not use the transformer aux bias supply as shown in your typical circuits. Rather VDD and RTN directly feed the 24V and 3.3V supplies, both of which simply turn on as voltage is supplied to them. 

What should I do with the VC_IN and VC_OUT pins?

Thanks! Jo

  • Hi Jo,

    See the following example schematic:


    UVLO_SEL - shorted to RTN to reduce the leakage current into VC_IN
    VC_OUT - leave floating
    VC_IN must be connected to a zener diode shunt circuit to keep it above UVLO. Be sure that R102 in the example is 0.25W rated

    Regards,
    Tom Amlee
    PoE PD Apps Engineer

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