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WEBENCH® Tools/LM5088: WEBENCH simulation vs quick start excel calculator evaluation tool

kevin eckstein3
Prodigy 150 points
Part Number: LM5088

Tool/software: WEBENCH® Design Tools

I am getting drastically different answers from the two tools. Which is closer to reality?

My design is 14-50Vin 12Vout 5A.    

oscillator in webench is 524kHz (10uH) but "quick start excel calculator" I need ~ 450kHz and gives error "part will enter low dropout model...". for the similar size inductor value.

My design goal is to maximize efficiency.

  • 0
    Prodigy 150 points

    Also when I try and change the UVLO voltage in Quick start toll it states I need a password. What is the password?

  • 0 in reply to kevin eckstein3
    TI__Expert 3320 points

    Hi Kevin,

    Seems Webench model is ignoring minimum Ton and Toff restrictions of the device ( TonMin = 55nS, ToffMin = 365nS) while creating the design. For your input case 14-50Vin 12Vout 5A, and with Ton and Toff restriction maximum frequency comes out tobe 408KHz. We will update the Webench model and let you know once these changes are available on ti.com.

    For your input case anything above 408KHz and we violate minimum off time restriction which forces device in low dropout mode. Excel calculator seems tobe using old values of TonMin and ToffMin and needs a update. I will forward the request to concerned team.

    If we need to keep the frequency (450KHz), then please consider moving VinMin from 14 volts to 15V. This should increase the maximum frequency limitation from 408KHz to 547KHz. For higher efficiency design, you can click on "Change Optimization" in Webench design and select high efficiency design (drawback higher footprint). 

    Best Regards,

    Bhushan

  • 0 in reply to Bhushan Waghmare
    TI__Expert 3320 points

    Hi Kevin,

    We have updated the Webench model. The fix should be available on ti.com by the end of March 2020. We will keep you posted once changes are available.

    Best Regards,

    Bhushan 

  • 0 in reply to Bhushan Waghmare
    TI__Expert 3320 points

    Hi Kevin,

    The updated model is now available on ti.com.

    Best Regards,

    Bhushan