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LM5109: LM5109 doesn't work correctly.

Hamid Kavian Athar
Intellectual 550 points
Part Number: LM5109


Hi forum,

I am using LM5109 to drive high-side and low-side n-channel mosfets. I am going to drive a three phase PMSM motor. when I drive an H-bridge, it looks fine. there are the wave forms:

LO pin;

HB pin:

HO pin:

HS pin:

HO and LO pins together:

finally here is my schematic:

when I drive three phases, they sink a lot of current of +9V power supply and the drivers don't work correctly. could you please tell me what I should do?

thanks in advance.

  • 0
    TI__Mastermind 32576 points

    Hi Hamid,

    Can you show me how all three phases connect together?

    Also, just to make sure the part isn't going into UVLO, can you measure HB to HS on the scope? You can use a differential probe or use the math function on the oscilloscope.

    Can you also measure HO to HS using the same technique?

    Best regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Intellectual 550 points

    Thanks Ethan for the reply. here is signal of pins 5 through 8 . 

    in this picture yellow signal (ch1) shows pin 8 (HB), light blue signal (ch2) shows pin 7(HO), the pink signal (ch3) is pin 6 (HS) and the dark blue signal (ch4) shows pin 5 (LO).

    if this image does not provided the information you are looking for, let me know.

    thanks.

  • 0 in reply to Hamid Kavian Athar
    TI__Mastermind 32576 points

    I can't quite read these images. Does your oscilloscope have the math function to subtract signals? If you use the subtract function to see HB-HS and HO-HS, that will make the waveforms a lot clearer.

    Also, while all three phases are on, can you measure VDD on the scope as well? I want to make sure the driver isn't going below the min operating voltage of 8 volts.

    Thanks for being patient with this.

    Best regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Intellectual 550 points

    sorry, when I was working on my board a power mosfet melt and unfortunately its pads damaged. therefore the pcb is not usable anymore. i have ordered another pcb. I will provide the images that you asked as soon as I receive the board.

    best regards,

    Hamid Kavianathar