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WEBENCH® Tools/LM25011: Webench does not allow Iout minimum to be specified

Robert puopolo
Prodigy 20 points
Part Number: LM25011

Tool/software: WEBENCH® Design Tools

I used Webench to design a 14-18V to 12 V switcher at .350 ma output. It is an incredible tool. I have a DC motor load that is on for only 20 seconds at a time.

1) How does the regulator behave with a dynamic load? I know this is complicated, but any way to estimate if damage can be done to the regulator and overshoot in response?

2) If a minimum load is needed, doesn't seem I can specify thru Webench, though other forms on the TI site allow minimum current to be specified for regulator designs.

Thanks,

Robert 

  • 0
    TI__Prodigy 700 points
    Hi Robert,

    first thanks for using LM25011 and Webench designer.

    1) The LM25011 is part of the COT regulators and known for fast load transient response / good dynamic response. If your concern is potential back EMF / voltage from potential large inductance of the DC motor load then you can place a diode across the DC motor with a filter cap.

    2) thanks for the finding. It is forwarded to the Webench team to look into.

    Hope that answers your questions...

    Best Regards,
    Robert L
  • 0 in reply to Robert Loke
    TI__Prodigy 700 points

    New_Rload_HotWire.docxHi Robert,

    some update on LM25011 Webench designer.

    The reported Rload bug will be fixed soon and the Webench team suggested some workaround for the time being. The workaround is to use startup sims in the “EDIT” mode and update the schematic Rload to a new resistor (the steps are in the attached word document).

    I hope this helps you going and maybe you would like to try your design in the lab on an EVM out.

    Best Regards,

    Robert L

  • 0 in reply to Robert Loke
    Prodigy 20 points

    Thanks very much for replying. I normally put the kick-back diode for all my designs. As it turned out I used the LM25011 in two different supplies on the same board, both work great, I would not have been able to accomplish without Webench.  

    The transient response is very stable, in isolation, the brushless motor at turn on peaks at 2.1 amps and decays to steady-state of 350ma 50-100ms out. I specified a 350ma load to Webench. In practice, when connected to the switcher, the 12 volts will dip to about 7 volts and flatten out within 16ms! No overshoot, just a clean exponential rise back to 12V. I assume increasing the output cap would help, but it works great for now.

    Robert Puopolo