TPS2372: TPS2372-4 function failure

Hi Gary,

TPH/TPL/BT pins are open-drain. When function fails, can you check the pin voltage on the chip side? Want to know if it is the BJT/3.3V failure or the TPS2372 pin failure. 

The NC pin should be leaved open. Does CVOUT connect to any nodes?

And could you let me know the resistance of the cycled resistors?

Best regards,

Diang

Hi Diang,

Cvout1 don't connect with anything.

R42 is 1kΩ.

R22 is 1MΩ.

We will test 3.3V/BJT later.

Hi Gary,

Thanks for your reply, please test the voltage one the pin directly.

I am wondering if 1M is too large for 3.3V bus voltage. Though the on resistance of TP pins is ~0.27V/2mA = 135 Ohm, and off resistance is 7V/1uA = 7MOhm. Is the 3.3V/1M=3.3uA current able to drive the BJT? 

Best regards,

Diang

Hi Diang,

We use two of TPS2372(U2 ＆ U3) to detect the power on the same Internet BUS. U2 is for the front 2x pairs and U3 is for anther 2x pairs.

We found that all the damage TPS2372 are U3.U3 is on the top layer of PCB and far away from D11 and C22.

U2 is on the bottom layer of PCB and its D15 and C6 are on the top layer and closed with U2_pin1.

What do you think about the layout. is it the IC damage reason that D11 and C22 are far away from U2?

Hi Gray,

Thanks for your updates. I will take a look and get back to you later.

Best regards,

Diang

Hi Gray,

Thanks for your patience.

May I know why two TPS2372-4 were used here?  

Two TPS2372-4 (dual-PD) normally are for two RJ-45 ports. If you only have one port there may be a risk that one TPS2372-4 is one and another is off. Then if both TPS2372-4 shared the same VDD-RTN buses without oring diodes, the off PD's TPH/TPL/BT pins may not stressed when the PD is off state. 

Can you share more details in the schematic? 

And do you think if one TPS2372-4 (up to Class-8, 71.3 W power) is enough in your case?

Best regards,

Diang

Hi Diang,

My customer indeed use 2x TPS2372 in this project and I think one of it is enough but customer has already finished the product. This product is used for measuring the functionality of POE and PD instead of powering devices through network cables.

Two of TPS2372 don't use same VDD but use the same RTN. U2 connects with first pair and third pair and U3 connects with second pair and fourth pair as below:

Hi Gray,

Thanks for your reply.

I will be out of office until Mar 27. Sorry for the delay response in E2E and thanks for your patience.

Best regards,

Diang

Hi Gray,

Thanks for your patience.

Since a FA request had been built, I will close this thread for now. We will have further discussion in email.

Best regards,

Diang