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LMZ12002 - Vin<Vout

Lucas da Silveira
Prodigy 110 points
Other Parts Discussed in Thread: LMZ12002

Hello,

I am using a LMZ12002 on a project and I would like to know:

If the feedback resistors of LMZ12002 are configured as so the Vout is 5v, what would happen if Vin<5v ? Will the MOSFET be constantly ON ?

and what Would happen if Vin is floating and a voltage of 4.2V is present in Vout ?

Thank you

  • 0
    TI__Mastermind 23835 points
    Hi,

    Are you using a battery at the output?
    In this case, if VIN <5V then the mosfet will shut off and if you have the battery at the output, the current will flow backward from input to the output.
    If the VIN is floating and you have battery at the output, then the VIN voltage will be equal to the battery voltage minus the voltage drop of the body diode of the internal MOSFET.

    Thanks
    -Arief
  • 0 in reply to Arief Hernadi
    Prodigy 110 points

    Hi,

    Yes, At the output there is going to be a linear charger in parallel with a reversed schottky diode charging a backup battery.

    Even if Vin is not low enough to disable the IC, is the MOSFET  going to remain OFF ? like a 4.5V input.

    Thanks

  • 0 in reply to Lucas da Silveira
    TI__Mastermind 23835 points
    Sorry, i just realized that your input is lower than your output.
    So yes, the mosfet will be on at maximum duty cycle try to meet the 5V but at the end it will not be able to get to 5V
    So at 4.5V input, the output most likely will drop to be lower than 4.5V (Vout is approximately 4.5V - MOSFET drop - Inductor loss)

    Thanks
    -Arief