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TPS2372: Please help to check dual signature application

user4206464
Intellectual 460 points
Part Number: TPS2372
Other Parts Discussed in Thread: TPS23881, TPS2378EVM-602

Hi expert,

For this data page 20, does PSE use 2 different RJ45 or 2 different channels? 

We concern that the VDD of 2 PSE channels, VDD1 of TPS2372(PD1) and VDD2 of TPS2372(PD2) are connected together.

When PD1 finish the handshaking, the VDD2 of PD2 will be pulled up to 54V, it will make PD2 handshaking fail. Like the attached waveform.

Channel3 finished the handshaking and power on, at the same time Channel is pulled up to 54V.

Is my reasoning right?

UpgradingIEEE802.3atandNon-StandardHighPowerPSESystemtoIEEE802.3btCompli....pptx

  • 0
    TI__Mastermind 40100 points

    Hi User,

    I recall looking at your schematic, you have diodes on RTN of each PD correct? If you didn't have diodes then yes, what you say is correct. However, if you have diodes on RTN of each PD, then the VDD-RTN voltage on PD1 should not find it's way to PD2.

    This means the only other way is if voltage from the PD front end, but I also recall in your schematic you have diode bridges so this shouldn't be the issue.

    The only way for to happen is if your schematic is bypassing the diode bridge or the series RTN diode. Can you help debug this?

    Otherwise, as I recommended in last post, you can either use the TPS23881 because PSE GUI can tell you directly what class/detection it sees on each channel.

    Also, you can take the TPS2378EVM-602 this has a similar configuration as your design (series RTN element and diode bridge). Can you test your PSE with this EVM to see if you have issues with that PSE?