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LM5051: LM5051 nFGD question

Red Yen
Expert 4360 points
Part Number: LM5051

Hi Support team 

According to the datasheet, when MOSFET is ON, INN PIN will be -100mV, nFGD will be high
When MOSFET is OFF, INN PIN will be -600mV, nFGD will be LOW
But the signal I measured at CH1 is -700mV, CH2 is also high, CH2 should pull LOW but not LOW.

may i have your comments?

CH1:PIN6 CH2:PIN4

  • 0
    TI__Genius 16305 points

    Hello Red Yen,

    This is not expected waveform, so could you confirm the measurement was made with reference to the INP/VSS pin voltage? I mean, is the INP/VSS pin connected to probe GND?

    Several factors can prevent the nFGD pin from indicating that the external MOSFET is operating normally. If the LM5051 is used to connect parallel, redundant power supplies, one of the connected supplies may hold the INP/VSS pin voltage close enough to the LM5051 INN pin voltage that the VSD(TST) threshold is not exceeded.


    Additionally, operating with a high output capacitance value and low output load current may require a significant amount of time before the output load capacitance is discharged to the point where the VSD(TST) threshold is crossed and the nFGD pin switches.

    Regards,

    Kari.