TPS2373: TPS2373 design issue(12V high current output)

Hi Penny:

I already follow your suggested add more loading. But need output more then 12V/0.4A.

The LED behavior stable(no blinking).But TPS2388x EVM GUI display"PSE output about 6W"

In addition, I tried to use the TPS2373-4EVM-758 EVB board. But the EVB board is only 1.94W. (LED display is correct)

What is the difference between these two designs? Could you have any idea for this issue?

Thanks!

Caspar 

Hi Caspar,

Please capture port current waveform with your board connecting to TPS23881EVM(use current probe at the cat 5 cable pair 36 and 45 or pair 12 and 78). Please compare the waveform when the load is 6W (when the LED doesn't blink) and light load (when the LED blinks). BTW, did you enable auto MPS function with TPS2373 on your board? Thanks.

Best regard,

Penny

Hi Penny:

I will follow your suggested compare the waveform.
But sorry I'm not so sure about auto-MPS.
Our circuit follow TPS2373 class-5 circuit design. Why you asked auto MPS function?
( Can it effect VCOUT voltage???)
About our product TPS2373 circit. Please see the below.

Thanks!
Caspar

Hi Caspar,

I thought you were seeing the LED on the PSE board blinking.  Am my understanding correct?

From the schematic, looks like the auto MPS is enabled. 

The auto MPS function doesn't change the Vout but it provides valid MPS signal to the PSE port to keep it on. Otherwise, the PSE port would be shut off if there'e no valid MPS current on the port. 

We will need to look at your port current and voltage waveforms. Thanks.

Best regards,

Penny

Hi Penny:

Sorry I'm not so sure about MPS function.
If I disable auto MPS function. Can it will effect any POE function?
about pair current waveforms. please see the below.
(I only posted pair 1 & 2 . because other pair the same this status)

Thanks!

Caspar

Dear Penny:

Thanks for your information. But this product is "POE splitter".

Customer can use 12V output power for any application.

Could you have any suggest about this issue?(add any load circuit on this circuit??)

Thanks!

Caspar

Hi Penny：

Thanks so much!
I will waiting for your information.

Caspar

Hello Caspar,

Can you take a waveform of the voltage across R30?

Additionally, can you state the differences between your schematic and the PoE reference design, including the front end?

Also as a side note, I am not the UCC AE, I am the TPS2373 AE :) 

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

Regards, 

Michael P.

Applications Engineer

Texas Instruments 

Hi Michael & Penny:

I already check my product about TPS2373 circuit. It almost the same as TI Class 5 EVB circuit.

But I still can double check it again.

About R30 waveform, please see below

• 745mW=> LED blink
• 8W=>LED no blink
• 80W=>LED no blink

Thanks!

Caspar

Hello Casper,

The Automatic Maintain Pulse Signature (MPS) function should be sending this signal when there is light load condition, but it looks like it is not. Can you compare the voltage on this pin to the voltage on the EVM that is working?

What could be happening is:

- the board is not built the way the schematic is

- parts are not populated correctly

- the IC is damaged 

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

Regards, 

Michael P.

Applications Engineer

Texas Instruments 

Hi Michael :
Thanks you for your replied. But the direction is very wide.
It keep difficult to lock in the problem.

About IC, I already exchange IC between EVB and my product. But the result is the same.
could you please provide class 5 EVB for test.

I really no any idea for this issue.

Thanks!

Caspar

Hello,

I would start with the components involved with Automatic MPS and the front end. If it is not the IC, and the schematics are exactly the same, then that leads me to believe either something is installed the wrong value, broken, backwards, something is shorted, etc. 

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

Regards, 

Michael P.

Applications Engineer

Texas Instruments