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Original question:

TPS2372-4EVM-006: TPL indication led is blinking

TPS2372-4EVM-006: unsupported device handshaking

omer nazir
Prodigy 50 points
Part Number: TPS2372-4EVM-006


Hi,

I designed a costum board by takind an example of TPS2372-4EVM-006 and it works. I have a problem when ı set resistor values of CLSA and CLSB.  I assigned CLSA pin as 63.4R and CLSB pin 90.9R for 70w power request from PoE switch (25w each port).

TPS2372-4 (or poe switch) isn't supposed to allow power (or handshake). I am always getting power 50v. (AMPS_CTL is  disabled or not)

when  I set CLSA pin as 63.4R, TPL indicator is always on even if I changed CLSB pin resistor value.

for CLSA pin as 90.9R, no indication is on. Changing the CLSB resistor value does not change the indication.

last one If I remove resistors, BT indication is on.

I don't want TPS2372-4 to handshake with the unsupported device.

Can you help to figure out the problem?

thank you 

Ömer

  • +1
    TI__Mastermind 37111 points

    Hi Ömer,

    Thanks for reaching out.

    When you set CLSA pin as 63.4R and CLSB pin 90.9R which is Class-8 configuration for TPS2372-4. PSE can send 90-W (45-W per port), and PD can receive 71.3W considering a 100-m Ethernet cable. 

    If your PSE could not support 90-W power, it will go into power demotion mode, which can only send 30-W out, and PD can receive 25.5W considering a 100-m Ethernet cable and 2-pairs. I think the PD will still accept the PSE even PSE can not support full power and goes into power demotion mode. You may need to use the TPH/TPL/BT pins to let the load MCU side take action in this case.

    Depending on the PSE is AT (Type-2) or BT 4-paris (Type-3,4), you could see the below two different LED combinations. 

    Best regards,

    Diang