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LM5117: Low Side FET Not Connected

Mark Ackerson
Genius 10190 points
Part Number: LM5117

Customer is having problems ATE testing the 0 ohm resistor connected between LM5117 LO pin and low side FET gate.  What would be the failure mode if this resistor is missing or not soldered properly?  Would the regulator work at all or could this be caught at final functional test?  Please advise.

Thanks,
Mark

  • 0
    TI__Guru 74232 points

    Hi Mark,

    If the low-side FET gate resistor fails open circuit, then the gate is open and may float high. In some cases, a pulldown resistor is present from gate to source that may alleviate this, but it is still not an active pulldown when the high-side FET turns on and SW increases at high dv/dt.

    In general, my recommendation is not to use a low-side FET gate resistor. The low-side FET is not used in the switching commutation process, only the high-side FET, hence a gate resistor at LO is not required.

    Regards,

    Tim