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TPS23753A: schematic

Hiroshi Sato
Expert 2590 points
Part Number: TPS23753A

Hello,

We are now checking our customer's schematics and let me ask some topics.

Basically, the customer had made schematics refer to TPS23753AEVM-235 for their pre-production,

however, some board  did not work well .We had found that there are some differences between their schematics and the EVM.  

1.

About ethernet transformer. The customer draw the power lines from primary side,

Is there  any potential to failure ? (in EVM, they are drawn from secondary side)

2.

In one  customer's board, only R281 and R282 had burned out.

Could you guess the cause ?

I attached their schematic (only around the transformer) and datasheet of their transformer.

3.

In the EVM schematic, "Additional EMI filtering may be required" is described.

In definitely, when we have to use it ? 

(for example, a ferrite bead is required when the trace length longer than 40cm. )

Thanks and best regards,

Hiro

PoE_Transformer.pdf

  • 0
    TI__Genius 9230 points
    Hi Hiroshi-san,

    I can take a closer look tomorrow.

    Thanks for the question,
    Tom A.
  • 0 in reply to Thomas Amlee
    Expert 2590 points

    Hello Thomas-san,

    Thank you for replying,

    I'm looking forward to get your comment.

    Thank you.

    Hiro

  • 0 in reply to Hiroshi Sato
    Expert 2590 points
    Hello Thomas-san,

    Can I get your comment by Thursday ?

    Thank you.
    Hiro
  • 0 in reply to Hiroshi Sato
    TI__Genius 9230 points

    Hiro,

    I greatly apologize for the delay. I had become sick last week. To address your questions:

    1. In the EVM, the power is actually drawn from the primary side, if you are considering the data side to be the secondary. As long as the center tap is on the same side of the transformer as the ETHERNET POWER input, you are good.

    2. R281, R282, R279, & R280 need to go after caps C195, C 194, C193, & C111, but before FG ground. Additionally there should be an ESD capacitor between the 4 75 ohm resistors & FG ground. It appears they did not do a proper Bob smith termination. If only R281 & R282 are burning out, it is probably because those pairs are where the power is being transmitted.

    3. The addtional EMI filtering would be necessary if you are not passing conducted emissions testing, you have a earth grounded load that creates a ground loop, or the switching from the power stage is messing with the integrity of your data signals. For more information, see this app note: www.ti.com/.../slua469.pdf

    Thanks,
    Tom

  • 0 in reply to Thomas Amlee
    Expert 2590 points

    Hello Thomas-san,

    Thank you very much for your sending comment, we'll discuss with the customer.

    Excuse me for pressing several times during your sickness.

    Thanks and best regards,

    Hiro