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Detecting Power Dropout to TPS2379

TIguru
Expert 1430 points
Other Parts Discussed in Thread: TPS2379

I have a question relating to TI's TPS2379 POE controller.  There is an output signal on the part, T2P, which is used for Type 2 PSE indication and also, from what I’ve read in the data sheet, an inrush current indication.  My question is this: Once the POE system is up and operating, if there’s a power dropout (48V drop out) to the chip, will we get an indication of this through the T2P indication?  I’m attempting to give my processor an early indication that power is lost.  We currently have the T2P interfaced through an optocoupler as shown on page 21 of the data sheet.  The output of the isolator goes directly into the CPU.  

Please advise.  Thank you!

TG

  • 0
    TI__Mastermind 41790 points
    Hi TG,

    If the power goes below the UVLO of the PD, T2P will release and go HIGH. However, note that if a type 1 PSE is connected to the PD, T2P will be HIGH so if there is a power drop, this pin will be ineffective in knowing whether voltage is dropped. The CDB pin might be a better choice. If you use it for SS, you will need a buffer so that the extra load does not effect startup.