• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 304 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS2378: TPS2378DDA

Shlomi Yehezkia
Mastermind 6150 points
Part Number: TPS2378

Hi Team,

My customer have a problem with the TPS2378DDA device

Vin- 48V

Current ~200mA

 

·         When they connect the system to DC in line it is working O.K. (POE is disconnected).

·         When they connect the system to POE (DC in is disconnected) with load the power is fluctuating.

See on the scope ~8V with ripple on the RTN pin and the system is not working.

·         When they connect the system to POE (DC in is disconnected) without load, the power Is OK.

After the power is stable and connect the load, the system is working OK.

 

Please help me to understand where is the problem.

 

Thanks,

Shlomi

Protection_and_Reset _ Protecti.pdf

  • 0
    TI__Mastermind 21320 points

    Hello Shlomi,

    Can you send a scope shot of VDD-RTN and VDD-VSS?

    Additionally, what is the load current for the system? 
    I think when the system has a load, the bulk capacitance is not able to charge and causes the output to be unstable. I would like to see the scope shots to test this. 

    Thank you.

    Regards,

    Michael Pahl

  • 0 in reply to Michael Pahl
    Mastermind 6150 points

    This is a scope plot of the power

  • 0 in reply to Shlomi Yehezkia
    TI__Mastermind 21320 points

    Hello,

    Thank you for the scope shots. So the IEEE 802.3 standard states that there cannot be a load for the first 80ms (this is listed on page 14 of the TPS2378 datasheet). What I believe is happening is the load is taking the current during in-rush which is not allowing the bulk capacitance to charge. This prevents the internal FET from turning on, which is confirmed in the scope shots. 

    I recommend either using a signal (such as CBD) or a microcontroller to delay the load until at least 80ms. Thank you.

    Regards,

    Michael Pahl