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WEBENCH® Tools/TPS54326: Vout Tolerance question

Steven Chen61
Prodigy 160 points
Part Number: TPS54326

Tool/software: WEBENCH® Design Tools

Hi,

I am using WEBENCH tool to design power solution and please explain the Vout Tolerance of WEBENCH for me so that I could know if it meets my demand for ripple & noise, I would like to know if the Vout Tolerance is contain DC voltage accuracy and AC ripple content.

I've tried using TPS54326 by this tool and get a value 2.61% for the Vout Tolerance, and my chipset's spec is 1% for DC voltage accuracy and 2% for AC ripple content, is it okay for the chipset?

  • 0
    TI__Guru**** 191445 points

    Steven,

    Stacking up all the tolerances is a little bit tricky.  But to start with the internal reference tolerance is +/- 1 % at 25 C. and about +/- 1.8% over temperature.  So if you need better than 1% accuracy over temperature, you may need to look elsewhere.  What chip set requires 1% accuracy?  Very few regulators have better than 1% tolerance on the reference voltage and then there are line, load and external component tolerances to consider.

  • 0 in reply to JohnTucker
    Prodigy 160 points

    Hi, John

    It's Broadcom's chipset and its operating condition spec as below.

    What I confusing is, is it just need the voltage tolerance meets the ±3% spec? Or we must separate the voltage tolerance to DC accuracy and AC ripple? But how could we check the DC accuracy and AC ripple separately while we measuring power noise? Please advise and thanks!

  • 0 in reply to Steven Chen61
    TI__Guru**** 191445 points

    Steven,

    For dc accuracy, you pretty much have to go from the specification, then add in tolerance for your voltage feedback divider.  For AC ripple, that is usually a measurement.  You can calculate it also, but you will find in real life PCB and component parasitics will limit the minimum achievable output ripple to 7 to 10 mV or so without a secondary filter on the output.

    I see there are multiple voltage rails required.  Have you considered using a multi-channel PMIC?  They are designed to power these types of applications specifically.     That is where I would look first.