TPS2378: TPS2378

Hi Oved,

Thank you for your question. 

The PoE applications engineering team is currently out of the office at this time and will respond to your post by end of day Monday, 6/8. 

Best Regards,

Brett Colteaux

PoE Product Marketing Engineer

Hello Oved,

The TPS2378 is a PoE PD device only. That means that it handles the power negotiation with the power sourcing equipment, but does not provide DC_DC control. 

So if your DC_DC is "in disconnected" then the system will probably not work since there is no DC-DC conversion happening. 

Additionally, part of the PoE standard is a Maintain Power Signature (MPS) signal. This signal tells the PSE that there is still something connected to the ethernet cable after initial power up. This signal is about a 10mA draw on VDD. The TPS2378 does not achieve this on its own, rather the DC-DC will draw this power. If the DC-DC is disconnected as you say, the PSE is probably powering up and then disconnecting power. 

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 again

this is the stage of the poe ic and the first dc-dc 
if I work with external power(dc in) in the top of the picture then everting is working good

but as I power the board from poe injector the board is starting up,everything seems to work good but after few minutes the board start like flickering and the current consumption is going down and the tps2378 start to worm

NOTE: the power consumption off the hole system everything is working is about 17W

please advise what is the problem in my board
about the poe injector I'm using 2 kinds

POE-48PBV2-EU

ADV-INJ30G

thanks a lot about your help

oved

Oved,

So you are saying the POE Injector and your board work for a few minutes with the TPS2378. Then the board gets warm, and the current consumption goes down. Does the IC get hot to touch?

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

Yes the ic get hot to touch