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TPS2384: TPS2384 Power always ON

Alexander Ncube
Prodigy 20 points
Part Number: TPS2384

Good day,

We are working on incorporating the TP2384 PoE PSE into our existing switch design so we followed there reference design in the TPS2384 Evaluation module (SLVU126D). The differences between this design and ours are as folows

1) I2C communication is not used so the clock, data and address pins are left floating

2) the device is always in auto mode (MS=0)

3) Only using 1 Port the rest are terminated according to (SLVA231A)

The issue is that the TPS2384 is able able to detect, classify and power an IEEE802.3af PD only once and afterwards the N pin is always grounded (Port 1). Measuring between RTN and this particular N pin if using a multi-meter in diode test shows a 0.7V drop.

Please correct me if I am wrong, If an Ethernet cable is not connected to the TPS2384 port the open circuit voltage is approximately 22V and when a cable is plugged in the detection cycle starts (4.4V and 8.8V) and in my case the voltage goes to approximately 48V with respect to RTN because the backup timer is implemented (ALTA/B == HIGH == 3.3V). This was observed the first time as expected.

But after a full detection, classify and power cycle, disconnecting the PD or even restarting the TPS2384 this particular pin is always 0V with respect to RTN which means that power is always supplied to the PD without classification or detection.

Whats causes this problem ? Is it possible that the TPS2384 chip is blown and if so why ?

Thank you,

Kind Regards,

Alexander M Ncube

  • 0
    TI__Genius 15685 points
    Hi Alexander,

    Thanks for using TI PSE! When you said restarting, do you mean you power cycled the board and there is still 48V across P and N? Is there anything between P and N that still consumes power after you remove the PD (like LEDs)? Thanks.

    Best regards,
    Penny
  • 0 in reply to Penny Xu
    Prodigy 20 points

    Hi Penny,

    Thank you for your response, when I say restart I am referring to power cycle and yes there is a 48V potential difference between the P and N pin of this particular port.

    And to answer your second question, there are no LEDs across the pins once the PD has been removed.

    I have even tried removing the 0.22uF capacitor but still no change.

    Thanks again,

    Alexander

  • 0 in reply to Alexander Ncube
    TI__Genius 15685 points

    Hi Alexander,

    Sorry for late response. 0.22uF is recommended for system stability requirement. Did you use AC disconnect or DC disconnect? Thanks. 

    Best regards,

    Penny

  • 0 in reply to Penny Xu
    TI__Expert 5615 points
    Alexander,

    It has been nearly a month since we last received an update from you.

    Are you still requiring our assistance? If not, please let us know so that we can close this thread.

    Thank you,