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LM5106 unstable output

Jean-Philippe Rey
Prodigy 240 points
Other Parts Discussed in Thread: LM5106

Hi,

I am using a board which contains two LM5106 (half-bridge gate driver), driving 4 MOSFET mounted in H-bridge configuration. I am driving a DC motor. The output of one branch is illustrated on the graph below:

As far as I understand, the branch turns "ON", and turns "OFF" 60 ms later, then the falling voltage slope is due to the induced voltage due to motor rotation. If I add some torque on the rotor, the falling slope gets more negative. If I add sufficient torque on the rotor, the "OFF" stage disappears and the bridge works well.

Why is the LM5106 driver is malfunctioning? I had a look at the datasheet, I know there is a undervoltage protection but the 12V rail, powering the driver as well as the bridge is perfectly stable. Why is the LM5106 working well when I add some torque on the rotor ?

Thank for any suggestions!

Best regards,

Jean-Philippe Rey

  • 0
    Prodigy 240 points

    Ok meanwhile I found it. As was driving my H-bridge with continous "1" input instead of PWM, the bootstrap capacitor couldn't stay charged. The workaround is to drive the h-bridge in PWM mode with dutycycle near 99%. This involves sufficient number of transitions to keep the bootstrap capacitor charged.

    !?#°@?&% bootstrap capacitors........

    Hope this could help someone a day.

    J-P

  • 0 in reply to Jean-Philippe Rey
    Prodigy 50 points

    I fell on the same catch. 

    Found solution before this post, but still happy to know that I am not the only one.

  • 0 in reply to markus.dnd
    Prodigy 120 points

    Hi We are using LM5106MM for motor drive application.

    When I load the motor I was able to stall the motor much before the rated torque and when we monitored the PWM which has pulses with in the ON time of the PWM. and motor voiltage is much lesser than the rated voltage.

    Then I changed the motor with a resistive load, the behaviour is same.

    Please let me know what is the cause, and why the driver is not able to drive the mosfets.

    Regards,
    Anoop