TPS23751: May we have 2 lan port PD (25W) solution?

Chu Stanley

Part Number: TPS23751
Other Parts Discussed in Thread: TPS2378

Hi Sir

My customer use tps23751 application in 1 LAN port PD (TPS23751) support 802.3at 25.5W and another one LAN is normal use(no PD function).

Currently new project, customer request both 2 LAN have PD function, but when we plug one port and another LAN port need disable.

May we have this kind reference design? what we need to notice in this kind application?

Another questions if TPS23751 plug 2 PSE, is the IC will be damage risk?

If we have 2port PD solution?

Bogey

over 6 years ago

0 Darwin Fernandez over 6 years ago

TI__Mastermind 41780 points

Hi Bogey,

In my opinion, customer should use two TPS2378 PDs and put them in parallel (connect VDD and RTN together). What will happen is if one PSE is connected to first PD, it will turn on to 48V and bias the VDD-VSS of the other PD. This will force the second PSE (when connected to the second port) to not pass detection and will not turn ON.

0 Raymond Liao over 6 years ago in reply to Darwin Fernandez

Prodigy 60 points

Hi Sir,

I don't have enough space to put two TPS2378PDs and one PWM IC on our small PCB dimension, I need to use similar TPS23751 PD with Flyback DC-DC Controller to reduce the placement space. Can you recommend me other solution?

If I want to use add two bridge diodes on each Ethernet port, and then connect to VDD and VSS together to only use one TPS23751 PD. Is there any side effect? I only hope not to damage any components, and also can accept this not work.

Raymond from CAMEO side

0 Darwin Fernandez over 6 years ago in reply to Raymond Liao

TI__Mastermind 41780 points

Hi Raymond,

Two of them connected to VDD-VSS would probably corrupt detection on both. How about use TPS23751 and parallel one TPS2378 at VDD-RTN?

0 Raymond Liao over 6 years ago in reply to Darwin Fernandez

Prodigy 60 points

Hi,

About this issue of two of them connected to VDD-VSS would probably corrupt detection on both, I want to experiment it on EVB board or our board. I don't concerned would probably corrupt detection issue, I can accept only hope expected it not work, so I hope don't any component damage happen includes PD and PSE side. How do you think?

0 Darwin Fernandez over 6 years ago in reply to Raymond Liao

TI__Mastermind 41780 points

Hi Raymond,

While I don't expect damage of components on the PD because it meant to handle 48V or the PSE (because the diode bridge will block the voltage), I have never seen VDD-VSS connected together for this type of application (I've only seen this for very high power PoE applications). But you can test it out on the EVM under your expected conditions to verify the solution as you mentioned. Be sure you adjust the detection and class resistors accordingly since both PD's will turn on detention/class resistors (not to mention the quiescent currents will double with two PD in parallel this way).

0 Raymond Liao over 6 years ago in reply to Darwin Fernandez

Prodigy 60 points

Hi Sir,

I have good news for these experiments on our board, it was workable solution for me. Of course as same you said that it was no damage of any components. So I only need to use add extra two bridge diodes on each Ethernet port, and then connect to VDD and VSS together at two bridge diodes of another Ethernet port for only use one TPS23751 PD. It was no side effect, it only have one Ethernet port of first plug in to sync up work from PSE to PD when two Ethernet ports to connect the PSE side together. So the PSE will always to establish on the one Ethernet port of first plug in.

When unplug either one Ethernet port, PSE will maintain to transfer another Ethernet port to reestablish it or still keep working it in one of the Ethernet ports.

Thanks a lot!

Raymond