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LMZ31707: Pre-bias limit on output before startup

Russell Wetherley1
Expert 4255 points
Part Number: LMZ31707

Hello E2E,

According to section 10.7, the device can start into a pre-biased voltage.  What is the voltage limit on this pre-bias?

Are there any corner cases where a 3v3 voltage on the output could harm the LMZ31707 before startup?  What if the pre-bias is larger than the voltage you want to start up in?

Thanks!

Russell

  • 0
    TI__Mastermind 35165 points

    Hi Russell,

    The regulator in this module uses diode emulation for improved light load efficiency so it has ~0A sinking current limit making it very robust with a pre-biased output. If the pre-bias is greater than the set output voltage, the regulator will go into skip mode and stop switching. The regulator will start switching once the output drops enough that the module needs to start regulating it.

    The one thing I can think of to be careful of is if this pre-bias source can source a lot of current, is present before the input voltage and the input can sink current. The pre-bias source could then push current backwards through the IC through the body diode of the HS FET to the input. The device would not be able to limit current flowing through it this way. However something like this can typically only happens in lab setting, not in a real application.

    Anthony