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TPS2373: APD

Kuan Wei Chen (Kevin Chen)
Genius 9710 points
Part Number: TPS2373


Dear Team,

Can you help on double check the APD pin design is correct or not?

Besides, if APD pin is higher than 1.65V, the hot swap MOSFET will turn off directly, right?

The customer mentioned higher APD voltage will have lower VDD voltage here.

Can you help on confirming it?

BR

Kevin

  • 0
    TI__Genius 9230 points
    Hi Kevin,

    We do not recommend this method. When APD is above 1.65V, the hotswap will turn off, which then lowers the voltage on the APD pin (due to the RTN referenced voltage divider). The PSE will then attempt detection, class, & inrush which then causes the APD voltage to rise again above 1.65V, turning the hotswap FET off, starting the cycle over.

    Instead, we recommend "corrupting" the detection waveform by implementing the circuit detailed in section 3.5 of our adapter OR-ing appnote: www.ti.com/.../slva306a.pdf

    Regards,
    Tom Amlee
    PoE PD Apps Engineer
  • 0 in reply to Thomas Amlee
    TI__Genius 9710 points
    Dear Tom,

    But TPS2373 have APD pin, why not utilize this pin?
    If we adopt your suggestion to use Vdd through photo and BJT to connect DEN pin, will it happen the same issue which I have right now?
    Or because a slight affect on the DEN will cause hand shaking fail here? Is this the reason you suggest connect DEN instead of APD.
    I think you can also suggest a APD solution here.

    BR
    Kevin
  • 0 in reply to Kuan Wei Chen (Kevin Chen)
    TI__Genius 9230 points
    Hi Kevin,

    The APD is intended for primary side adapter oring (option 2). To confirm, is their adapter on the output of the power converter (option 3)?

    With their current implementation, the PSE would continually try reconnecting. By purposely failing detection, you can insure that the PoE handshake sequence will not progress further than detection & not keep retrying inrush (which may cause thermal shutdown).

    Regards,
    Tom Amlee
    PoE PD Apps Engineer