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TPS54429 / Routing FB and VO line

S.Satoshi
Guru 21685 points
Other Parts Discussed in Thread: TPS54429

Hi,

Please let me ask about routing the FB and VO line of TPS54429. I'd like to know the reason why the FB and Vo line are routed separately from Vout but it can be bifurcated near each pin. Please refer the inserted drawing and give your comments.

Your quick and thorough response will be appreciated.

 

Best Regards,

Sonoki / Japan Disty

  • 0
    TI__Guru**** 191445 points

    The VO and VFB pins serve two distinct and different functions even though they both are sourced from the output voltage node of the converter.  VO is used for the adaptive on time control and is used to set the on time for each switching cycle.  The VFB pin is connected to the hysteretic off time comparator.  Additionally there is ripple injection applied to that node by the internal DCAP2 circuitry.  It is best to keep the two traces isolated as much as possible.  For the EVM and system evaluation boards, we designed immediately for best practice by routing separate traces from the output point of regulation to the VO pin and the resistor divider network to the VFB pin.  You may possibly be able to run a single trace, but I have not tried it. 

  • 0 in reply to JohnTucker
    Guru 21685 points

    Hi John-san,

    Thank you for your quick response! I understand that the functions of these two pins and so is should be kept the two traces.

     

    I'd like to ask one more about this. Can you estimate what will happen if the FB pin and VO pin are connected near each pins?

     

    Best Regards,

    Sonoki

  • 0 in reply to S.Satoshi
    TI__Guru**** 191445 points

    I have never tried it.  I expect the differencess would be subtle.  On an EVM, you may not notice it.  It could have more of an effect on a user PCB with potentially more noise sources.  For most layouts, it is really not all that difficult to run two parallel lines from the point of rgulation back to the IC.

  • 0 in reply to JohnTucker
    Guru 21685 points

    John-san,

    Thank you for your comments. I'll try it by using EVM by myself !!

    Best Regards,

    Sonoki