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webench design reliability?

or nsl
Intellectual 280 points
Other Parts Discussed in Thread: TPS54340

Hello,

I designed with webench on tps54340 a couple of months ago and when i got to test the pcb according this design, the output voltage is less than it should be

- Output should be 5v with/without load and in the test - got 4.85v load 1A and 4.73v @load 2.09A):

In addition, i made a new webench simulaltion today with the same parameters and it gives a different valeus for Rcomp (24.9K instead of 26.1k) and Ccomp2 (20pf instead of 16pf) (all rest are the same).

Question - can Webench be trusted for correct designs outputs for selecting the correct valeus of ressistors and capacitors ets'?

byd, all tests made in lab with 25 celsiouse and proper conditions.

thank you in advance,

WebenchReportsServlet.pdf

 

  • 0
    TI__Guru**** 191445 points

    I suppose webench could calculate slightly different values.  Can you provide your inputs?  I will try it.  in any case, those changes are pretty small and will not have much effect on the loop response.  I almost never use webench for compensation design though.

    The calculation for output is pretty straight forward.  What value FB resistors are you using?  How are you measuring the voltage?  Right at the point of regulation?

  • 0 in reply to JohnTucker
    Intellectual 280 points

    Hi John,

     

    Thank you for your reply.

     

    The inputs was: 10-24vin, 3A Iout and 5v Vout. The FB resistors used 10.2k and 53.6k as to the webench design which I attached on my post previously. Measurement of the output voltage measured on the pcb contacts at point of regulation.

      

    Thanks

     

  • 0 in reply to or nsl
    TI__Guru**** 191445 points
    Those resistors calculate to 5.004 V output. If your PCB is well designed and your measurement technique is correct, you should get much better regulation than you report. You also have to follow the BOM exactly. Load regulation on the EVM is better than +/- 0.6%, or about +/- 30 mV for %V output. Although I don't personally use Webench for designs very often, it should give correct values. You can always double check them by hand.
  • 0 in reply to JohnTucker
    Intellectual 280 points

    I followed webench bom and testing methode but didnot get 56k resistor on first webench simulation, now if doing this simulation it gives different resistors and caps valeus including 56k res, maybe webench valeus needs to be checked manualy and only meant for overall refernce.

    thank you