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LM5101A High output issues

Travis Mckane
Prodigy 10 points
Other Parts Discussed in Thread: LM5101A

Hi,

I've been working with the LM5101A for a week now and have been having some trouble getting a signal out of the HO output of the IC.

Right now these drivers will be sending a signal to a half H-bridge that will power a 1 phase of a 3 phase motor.  

I am using IRF3806 FETs for both my high and low side of each half h bridge.  I initially tried to test the LM5101A's without hooking up the HO to the gate of the high side transistor just to see if there was an output waveform that would be larger than the input (HI).  I can confirm on oscilloscope that I am inputting proper PWM waveforms, I can also confirm that the LO, low side output of the drivers, are outputting the proper waveform for my low side FET.  The issue is that the HO output is independent of the HI PWM input.  The waveform that is outputted on HO is the DC rail voltage, Vcc inputted on the  IC.

I have a proper bootstrap capacitor (4.7uF) and a decoupling cap from Vcc to VSS.  I am not using an external bootstrap diode.

Any help would be appreciated.

Thanks

  • 0
    TI__Intellectual 2320 points

    Hello Travis,

    During the normal operation, the HO output (HIGH) for the driver should be the V(HB) -V (HS).The bootstrap capacitor you  presently have in the circuit (4.7uF) is too big. You should try with a smaller rating capacitor. A 0.1uF cap should be sufficient. Is it possible for you to send the circuit schematic?

    Regards,

    Sourav Sen