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TPS23731: DEN pin detect disable

Tommy Tzeng
Genius 5780 points
Part Number: TPS23731

Hi Team,

we want to use the dual input function, and also use the APD pin for the auxiliary power detect input, but we don't the LEDs of T2P & APDO to light up.

can we pull the DEN pin to GND? have any risk? or any suggestion to us? thanks.

  • +1
    TI__Mastermind 37121 points

    Hi Tommy,

    I am wondering how you configure the dual input. Is it PoE PD + 48V DC adapter?

    T2P and APDO are output pins, you can leave them open and it won't influence the APD's function. You can add a resistor divider on the DC adapter input side, when APD is high the PD's internal hotswap will be turned off to let the DC adapter has a higher priority. 

    Pulling DEN to VSS will force the PD to off too. But it normally need an optcoupler since VSS will be disconnected to RTN after hotswap is off. If your adapter refers to RTN, using APD is recommended. 

    Best regards,

    Diang

  • 0 in reply to Diang Xing
    Genius 5780 points

    Hi Diang,

    the attached file show warn after customer test Sifos_802.3at, may we know hoe to improve or modify any test methos? 

    thanks for your support and learn from you.

    3270BE-PD test-low limit-20240612.xlsm

  • +1 in reply to Tommy Tzeng
    TI__Mastermind 37121 points

    Hi Tommy,

    Thanks for update.

    IlimMinViolation WARN happens when you draw > 400 mA current from PSE in 0 - 1.5s period when the PD hotswap is on. Kindly increase the startup circuit delay time. In some cases, adding decoupling capacitor is a valid way to offer the transient turn on current and avoid the PD drawing high current from the PSE during transient. The layout to ensure these ceramic caps have a short path is important to achieve lower stray inductance and better effect. 

    Vhyst WARN happens when rising / falling UVLO difference less than 2.8V in your case. TPS23731 PD can be ~6V. For TPS23731 PWM CTL, you can try to increase the LINEUV lower resistor to let DC/DC turns off at a lower voltage.

    Best regards,

    Diang

  • 0 in reply to Diang Xing
    Genius 5780 points

    Hi Diang,

    thanks for you grest support, we will let customer try it.

  • +1 in reply to Tommy Tzeng
    TI__Genius 15275 points

    Hi Tommy,

    Thank for your response, I will mark this thread as closed. If you need further support, please feel free to open another question on E2E, thanks!

    Regards,

    Brandon