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LM3485: Minimum Load Current

Jim Gavin
Intellectual 920 points
Part Number: LM3485

Is there a minimum load current for the LM3485? I like the idea of using the LM3485 for my application since it has a very high load transient response. In my application I will be dropping from 18V to 12V and the load will be switched on/off via PWM, so the load will go from 0A to 2.5A and back to 0A very quickly. I also have a condition where the load is completely turned off and I want to make sure this is not an issue for the LM3485.

  • 0
    TI__Mastermind 30430 points

    Hystertic control architecture requires just inductor ripple, generated by the switching action of the device. This will cause sawtooth ripple on FB node, in addition on output. The ripple on output can be minimized by having feed forward cap to couple ripple on FB node and achieve required ripple amplitude without needing to account for feedback divider ratio.

    To answer your question, no, though be aware your switching frequency will vary a bit.

    COT, a variation I guess of hysteretic architecture overcomes the above downfall of pure hysteretic architecture.

  • 0 in reply to Marshall_Beck
    Intellectual 920 points

    I'm assuming that the sawtooth ripple will be at the PWM frequency and vary slightly with the PWM duty cycle of the load. Is that correct?

    When you say that the switching frequency will vary are you referring to when the load is actively being PWM'd or when the load is turned off?

  • 0 in reply to Jim Gavin
    TI__Mastermind 30430 points

    The ripple wiill be at the switching frequency of the regulator.

    Figure 20,21 will speak to the frequency variance. Demonstrated is frequency variance with vin and iout.