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DS90UB953-Q1: Disconnect DS90UB953 from DS90UB954 while power supply is working

Part Number: DS90UB953-Q1

 Dear Sir,

In my case, my customer maybe disconnect the DS90UB953-Q1 board from DS90UB954 board while the system power is working, and POC power mode is used in my case.

Is there any damage risk for both of DS90UB953 and DS90UB954?

For example, the energy stored in Induce and Cap will go through the AC couple cap and into RX and TX pins , Can this energy damage 953 and 954?

Best regards,

David

 

Tiger

  • I can't get your issue well. since you disconnect UB953 and UB954, why Power can be delivered again?
    anyway, please follow up TI's PoC design, it is ok even if you had no high speed signals from UB953 to UB954.

    best regards,
    Steven
  • In reply to Junqiang Shi:

    Dear Steven,

    In fact, 953 are connected with 954 HUB with push-pull connector, sometimes the customer need to replace the 953 but forget to turn off the system power.

    The energy stored in INDUCE(POC couple INDUCE) will go back to TX pins of 953 , I think it maybe destroyed 953 by this huge induced voltage, is it right?

    Best,

    David

    Tiger

  • In reply to Tiger Wang:

    the in-parallel resistors with inductor provides engergy discharge, and the high speed pins are safe.


    Steven
  • In reply to Junqiang Shi:

    Dear Steven,

    I had not seen the resistor paralleled with induce in EVM or datasheet schematic, if a resistor paralleled with INDUCE, the power noise will couple with the signal,I think it is not good for stable high speed communication.

    David

    Tiger

  • In reply to Tiger Wang:

    I think you ignore it in our ref. design. May I know your PoC  design in your sch.? I will point out it.

    regards,

    steven

  • In reply to Junqiang Shi:

    Dear Steven,

    Is it R25 in 953EVM schematic?

    David

    Tiger

  • In reply to Tiger Wang:

    Dear Steven,

    If POC is not permitted(J15 is open) and powered by external power, all POCrelated components, L4,L5,R35,L7//R25, are still be on PCB.

    I want to know how these components impact on SI, signal integration? the STUB is also just like an antenna, EMC/EMI may be a big risk.

    If I design my hardware like Ref design, can you give me some advice and avoid these concerns?

    David

    Tiger

  • In reply to Tiger Wang:

    sorry I can't understand your issue well. pls paste your sch. for review.
    for emc/emi, pls refer ub953/954 d/s on one layout example which is used to reduce stub.

    steven
  • In reply to Junqiang Shi:

     Dear Steven,

    Please see the red rectangle, if POC mode is not used, do  these components in red rectangle impact the SI and also arise EMI issue?

    Tiger

  • In reply to Tiger Wang:

    The highs speed signal does not care for whether the power supply is deliver or not if PoC network is alive. from AC viewpoint, the DC power supply is believed as "grounding" as well. So it has no issue for such application. Also, please be careful the high speed signal layout, the EMI is under control.

    best regards,
    Steven

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