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TPS2378: Change from adapter to PoE power source of TPS2378

takahiko yokota
Mastermind 7135 points
Part Number: TPS2378
Other Parts Discussed in Thread: TPS23753,

Hi

My customer will design the circuit of option3 in "Advanced Adapter ORing Solutions using the TPS23753" using TPS2378.
According to  this document, there are the times to change from adapter to PoE power source.
Could you tell me these times?

Best regards,
Yokota
  • 0
    TI__Genius 9230 points
    Hi Yokota,

    Typically, the amount of power available to the PSE is not enough to power every downstream PD device, so power must be budgeted. Because of this, a customer may use adapter priority so that PoE can be a backup supply if an AC mains connection is not available near where the PD is deployed.

    Let me know if this answer your question.

    Regards,
    Tom Amlee
  • 0 in reply to Thomas Amlee
    Mastermind 7135 points
    Hi Tom-san

    Thank you for the reply.
    My customer consider powering from PoE if AC adapter came off.
    So they would like to know the time to change from AC adapter to PoE.
    Could I get that time?


    Best regards,
    Yokota
  • 0 in reply to takahiko yokota
    TI__Genius 9230 points

    Hi Yokota,

    The time it would take for the PD to switch to PoE input would be in the hundreds of miliseconds. PD & PSE would need to perform detection, class, then power on. This is a long enough period of time for the output voltage to drop.

    To shorten this amount of time, see section 3.6. It talks about keeping the PSE connected to the PD while the adapter has priority. I do not have the time length for this kind of transition, but it would not be long enough to see a noticeable hit on the output voltage.

    Regards,
    Tom Amlee
    PoE PD Apps Engineer