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LM61440-Q1: Issue Creating Webench Design Under 3A Iout

Antonio Fadhel
Genius 9410 points
Part Number: LM61440-Q1

Hi Team,

My customer is trying to run a Webench simulation for the LM61440-Q1: 8V-24V input, 5V output, 1.1A out, 1.1MHz fsw preferred, for a USB application. However, if they select an Iout of 3A or lower Webench returns a stability error and cannot generate the design. Any idea what the issue with the design would be? My guess is that it is recalculating the external components for lower pk-pk ripple current and resulting in values that lower phase margin, but the design parameters seem well within the capabilities of the device. 

Looking at Table 3 and adjusting for their design parameters, I would think a 3.9uH inductor 3x22uF 16V caps, and 22pF Cff should work well for 5V/1.1A/1.2MHz. Please let me know if you see any issues.

Thanks,

Antonio

  • 0
    TI__Guru 50120 points

    Hi Antonio,

    Thanks for bringing this up to my attention.

    I will need to contact the WEBENCH support team to understand why this is resulting in a design issues.

    I was able to confirm that for 3A the WEBENCH result shows error. However if you changed the input to 4A the WEBENCH design was able to simulate the circuit.

    It may be a coding/program issue.

    I'll let you know when I hear back from the team.

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    TI__Genius 9410 points

    Thanks, Jimmy. Please keep me posted.

  • 0 in reply to Antonio Fadhel
    TI__Guru 50120 points

    Definitely. I just got the issue assigned so hopefully I hear back from the support team soon.

  • 0 in reply to Jimmy Hua
    TI__Guru 50120 points

    Hi Antonio,

    I had the WEBENCH support team help with fixing some coding issue that cases unstable design for this device(seen in other e2e posts as well). The model should be online within a week from today. 

    Please wait until next week to check the latest WEBENCH model of this device.

    I will be closing this thread for now. If you have further questions after using the model, please reply to this thread and we can continue this discussion.

    Regards,

    Jimmy