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TPS23731: detection FET bridge

JDJ
Expert 4486 points
Part Number: TPS23731

Hello,

In our testing, the TPS23731 PD chip failed to power on. The PoE PSE is designed to 802.3bt standard and the failure happens in the detection phase of initial ack. Here is a sample of the waveform on the PSE Mode0 and Mode1 pins in accordance to bt standard.

The default detect voltage setting for this controller on the low end is set to 4.8V and the high end is 8V in the above waveform. It appears that detection FET bridge turns on much before than it is supposed to.

Thanks

  • 0
    TI__Mastermind 37121 points

    Hi JDJ,

    Thanks for reaching out.

    Could you share the schematic of your PD design? The ideal diode bridge should turn on after the PD-PSE detection and classification. Better to turn on the FETs when VDD-VSS is higher than 20.5V (normally 25 - 30 V if no low voltage dc adapter or passive injector at VDD-VSS).

    Best regards,

    Diang