TPS2372: power up issue

Sam Ting

Part Number: TPS2372

Hi team,

We have a PD design with TPS2372, but have power-up issue as shown below, the voltage waveform was measured from VDD and VSS pins.

The PSE is standard IEEE802.3af and the load between VDD and RTN pins is 200 Ohm.

Could you help check the schematic and provide the suggestions to solve the issue? Thanks!

Schematic:

Best regards,

Sam Ting

over 3 years ago

0 Michael Pahl over 3 years ago

TI__Mastermind 21320 points

Hello,

If the PSE is only IEEE802.3.af, then it can only provide up to 13W of power (Class 1-3).

Overall, the PD is set to class 8 (71W), and CLSA pin has 63.4ohm. A IEEE802.3.af PSE will not recognize this as a valid class since it only knows up to class 3. That is why it is not powering up.

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards,

Michael P.

Applications Engineer

Texas Instruments

0 Sam Ting over 3 years ago in reply to Michael Pahl

TI__Intellectual 2710 points

Hi Michael,

Therefore, we should modify R_CLSA / R_CLSB to one of the 0-3 class definitions in the table below. Is this correct? Thank you!

Best regards,

Sam Ting

0 Michael Pahl over 3 years ago in reply to Sam Ting

TI__Mastermind 21320 points

Hello,

Yes.

Additionally, if you are new to PoE, please see our training portal: https://training.ti.com/power-over-ethernet-poe-training-series

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards,

Michael P.

Applications Engineer

Texas Instruments

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TPS2372: power up issue