TPS2378: What happens if TPS2378 get 48V direct input without Detect/Classification?

Nicky Lim

Genius 3195 points

Part Number: TPS2378

Hello,

Make TPS2378 circuit as below.

Power source is only PoE Injector which does not have PSE function.

So, TPS2378 gets 48V directly from injector without Detect/Classification function.

At that time, its output voltage is around 7V, not 48V.

Why this kind of problem is occurred?

Please check below schematic and let me know the root cause.

Regards,

Nicky

TPS2378.pdf

over 6 years ago

0 Thomas Lewis over 6 years ago

TI__Expert 5615 points

Nicky,

My apologies for the slow response here. Our team was short staffed last week but I wanted to let you know that your question has been received and you will receive a reply on Monday latest.

Thank you for your local support and promotion of PoE products from Texas Instruments,

0 Darwin Fernandez over 6 years ago in reply to Thomas Lewis

TI__Mastermind 41790 points

Hi Nicky,

By output, do you mean VDD to RTN? Or VDD to VSS?

If RTN, then the PD controller is probably folding back and you need test with no load first, then increase load after VDD-RTN is 48v.

If VSS then the injector is folding back and the load may be too high that injector cannot provide the power. Please confirm. Thanks!

0 Nicky Lim over 6 years ago in reply to Darwin Fernandez

Genius 3195 points

Hi Darwin,

Output is VDD to RTN.

Could you let me know what means the PD controller is folding back? and how can fix it?

And could you review attached full schematic?

Regards,

Nicky

TPS2378 sch.pdf

0 Darwin Fernandez over 6 years ago in reply to Nicky Lim

TI__Mastermind 41790 points

Hi Nicky,

Let's check first if this is the issue we need to solve. Can you try removing L402 just to see if VDD-RTN can turn ON to 48V? Thanks!

Power management

Power management forum

TPS2378: What happens if TPS2378 get 48V direct input without Detect/Classification?