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DRV8243H-Q1EVM: Voltage drops in output signal

Part Number: DRV8243H-Q1EVM
Other Parts Discussed in Thread: LM74610-Q1

Hello everyone,

I have a DRV8243H-Q1EVM. When I connect a motor and operate the bridge with PWM, I have periodic voltage drops on the output side.

The signals can be seen on the attached oscilloscope image. Could this error be caused by an incompatible setting?

We want to drive a motor in bidirectional mode with pwm control.

I have made the following settings on the test board:

ITRIPI LVL2

IPROPI 1kOhm

DIAG LVL1

SLEW RATE LVL1

MODE LVL3

I have a 12V DC motor. The motor turns and I can also control the speed and change the direction via PWM.

I only let the motor run at idle and you can hear how the motor goes down with the speed for a short time when the voltage has a negative peak.

When idling, the motor draws approximately 0.8A.

I tried this with the GUI from TI and also with an external ST µC. The result was the same.

The error also occurs if I only set the controller to awake in the GUI and set the Enable Driver to Enable without setting a PWM or start the drive.

Many thanks in advance.

  • Hey Bernhard,

    A few debug questions:

    1. Does it occur periodically?  Every 1.4 seconds? 
    2. In your scope shot above, were you running at 100% duty cycle?  It looks like 100%, else we would see the output PWM from 0 to 12V and back. 
    3. What is the state of nFAULT during this event, I'm having trouble making sense of the digital lines in your scope shot.  Looks like nFAULT stays high the whole time? 
    4. Can you try with a different motor model to see if a completely different motor results in the same issue with this driver?  Ideally something with different capacitance/resistance, not just another copy of this motor.  Wondering if this issue follows the motor or the motor driver. 

    I tried to recreate your issue on a DRV8245 EVM but could not replicate it.  I have requested a DRV8243H-Q1EVM, but it will be a few days before it arrives for me.  

    Best,

    Jacob

  • Hey Jacob,

    1. Yes, it occures periodically.

    2. Yes in the scope I had set 100% duty cycle but I also tried with other duty cycles with the same result.

    3. The nFault is high and is never down after the reset on wake up.

    4. I also tried another motor but the result was the same.

    I connected the power supply on the grey conector.

    When I connect the power supply parallel also to the red VM connector and the black GND connector the negative peaks disappear.

    So I have a solution, but I can't figure out why I also have to cennect the power supply also at these two connectors.

    Greetings 

    Bernhard

  • Hey Bernhard,

    Very interesting.  Given that, I wonder if it is a manufacturing issue on our reverse polarity protection or filter circuit on the input.  The below circuit is connected between the grey connector and the VM net (red VM connector).  Can you look on your EVM and make sure C51 and the other components around it look soldered correctly? 

    Can you also take a scope capture including the VM voltage signal along with the motor waveform, measured at the big red connector?  Want to see if VM dips momentarily at the same time as well or not. 

    I will test this out on my DRV8243H-Q1EVM once it comes in.  

    Best,

    Jacob

  • Hello Jacob,

    the solder joints look OK and I can't see any other damage or anything like that.

    Here is the picture of the voltages: (The voltage drops can also be seen in the VM voltage)
    Green is the motor voltage OUT2 and orange is the VM voltage.

    Greetings,

    Bernhard

  • Hey Bernhard,

    I have discovered the cause of this.  It is a feature of the LM74610-Q1 Zero IQ Reverse Polarity Protection Smart Diode Controller on the EVM.  https://www.ti.com/lit/ds/symlink/lm74610-q1.pdf#page=9 The device has a Zero IQ design, and it needs to have this 2% off time to achieve this.  It results in a voltage drop of 1 body diode forward voltage drop for 2% of the time.  

    As you discovered, you can bypass this by powering the EVM directly from the red banana jack connectors.  

    Best,

    Jacob

  • Hello Jacob,

    thank you very much for the quick and competent answer. :)

    Best regards
    Bernhard