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LM43601: low consumption mode with 5V IN and 5V OUT

Alexandre BALDINO
Intellectual 520 points
Part Number: LM43601

Hello,

I use the LM43601 simple switcher in many designs.

I've selected this component because of its EMC and low current performances.

It works fine when supplied by a 15V source.

When my system goes in standby mode, the LM43601 is supplied by a 5V source. And I need a 5V output which delivers around 300µA.

So I suppose the simple switcher will not switch anymore (will stay closed), and will still be able to drive a current around 300µA with an output voltage around 5V.

But the experiments don't give this theoretical result.

May be there's something wrong in my design, but I'd like to know if my supposition (5V in ~5V out with 300µA load) is correct?

Thank you

Best regards

Alex

  • 0
    TI__Mastermind 23845 points
    Hi,

    I believe you are operating in dropout mode when VIN is approximately equal to VOUT. There will be a minimum off time of 100ns as well as efficiency at 300 uA of load current that will limit makes your VOUT is slightly lower than 5V. The part will still switch because it is not at the VIN UVLO level.

    Thanks
    -Arief
  • 0 in reply to Arief Hernadi
    Intellectual 520 points

    Hi,

    Thank you for your answer.

    So, how can I get the efficiency or the input current consumption please?

    Best regards

  • 0 in reply to Arief Hernadi
    Intellectual 520 points
    I forgot to write that I need an ultra low input current, and in this case (5Vin - 5Vout 300µA), how can I get its value?
  • 0 in reply to Alexandre BALDINO
    TI__Genius 11085 points
    This condition is not a regular operating condition for a buck converter. It is a dropout condition when the regulator tries to maintain Vout as much as it can, but due to low Vin, it can only do so much.

    The light load efficiency is high with this family of parts because it operates at very low switching frequency at light loads, with decent about of room between Vin and Vout. But with Vin very close to Vout, the ripple current is really small, it will not trigger PFM mode and foldback the frequency to very low. The switching frequency will foldback to about 1/8 of the RT frequency. The input current from the supply will be much higher than Vin=15V condition.

    If input current from supply is a critical parameter, you could use a bypass LDO to supply the 5V under standby condition. Or switch the output of the LM43601 to 3.3V in standby. Or raise the standby Vin to 7.5V.

    Hope these helps,

    Yang
  • 0 in reply to YangZhang
    Intellectual 520 points

    Thank you Yang, your answer is clear.

    I need to design a solution in low power mode.

    Thank you again.

    Best regards