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LM5123-Q1: En/Dis the device

Ohad Fundoianu
Intellectual 270 points
Part Number: LM5123-Q1
Other Parts Discussed in Thread: LM5121

Tool/software:

Hi Harry, 

Does the UVLO_EN pin allows when connected to a HOST (MCU) in addition to its resistor divider, to shut-down the LM5123-Q1 when pulled low by the HOST? Is it, as a result of shut down, turns off the HO and LO outputs in a way that the two high and low FETs are turned off and no voltage transferred to the Drain of the high FET? 

Thanks, 

Ohad

  • 0
    TI__Genius 15755 points

    Hello Ohad,

    Thanks for starting a new thread for a different topic.

    Yes, it is possible to connect an MCU in addition to the UVLO resistor divider to shut-down the LM5123-Q1.

    During the shutdown, both gate driver outputs, HO and LO, will be low and both FETs are turned off.

    But, with a regular BOOST topology it is NOT POSSIBLE to disconnect the output.

    The High-side FET has a built-in body diode which will always be conducting when Vin is bigger than Vout.

    Already before the controller is enabled for the first time, this diode will be conducting and charge the output capacitors to the input voltage (minus a diode drop),
    and it will also supply the load with that voltage.

    You will need another "breaker" in series which will allow to disconnect the load / output.

    The LM5121 has a control for such a breaker FET built in.

    Best regards
    Harry