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DRV8838 reverse direction

Hi,

I am using and Arduino MKR1000 with the DRV8838 driver board.
Arduino VCC (3.3V) on DRV8838 VIN pin.
Arduino GND on DRV8838 GND pin
9V power supply

When I leave the PHASE pin LOW my output from the DRV8838 looks perfect, at any frequency i set it.

When i turn the PHASE pin HIGH my output looks like the photo below, always 1000hz. pulses during on “ON” phase of the PWM (when the output should be at -9V). This is at 100hz 50% duty cycle.

It has nothing to do with my code as I can simply apply 3.3V to the PHASE pin from VCC on the arduino and the output changes from the first photo to the second photo.

Motor was disconnected in these tests.
Soldering looks good

Please help.

Could you post pictures of your setup that show all connections including solder joints? Did you ever connect the driver to a motor and if so, could you post documentation for it? Did the driver ever work for you?

-Claire

I am having the same issue. I can only drive the motor one direction. My setup is below:

Power supply : 6v going to motor power, 5v going to logic in
Signal generator : 21kHz signal, manually changing the duty cycle, 0v-4v Peak to Peak. grounded with the power supply and connected to ENABLE pin
Scope: yellow channel is PWM signal, blue signal is the motor power channels

When the Phase pin is connected to 5V the motor spins. If the Phase pin is connected to ground, the motor will not turn. Also, if the Phase pin is left floating I get the same sort of noise on the motor output channels.




Hi.

The connections in your picture look okay, but it would be helpful to see pictures of the whole system that show all connections. My immediate suspicion in cases like these is a bad power or ground connection, so you should double-check that all of your wires (from both supplies, signal generator, and DRV8838) are making solid connections and that you are measuring the expected voltages on VCC and VIN. Also, could you try to disconnect the motor and use a meter to measure the driver’s output?

-Claire

100% sure there is no issue with power or signal. Vcc and Vin were measured with multimeter and match the values shown on the power supply.

Without the motor, I still see no output on reverse. The setup shown above was without the motor connected.

As I am the second person to see this issue, I suspect something is wrong with the drivers itself.

For context, we have sold many thousand of these boards and have not seen any larger pattern of complaints, so it seems very unlikely that there was a systematic defect with the driver. It is possible to damage just one side of the H-bridge on drivers like this, and your particular board could of course be damaged.

Looking back at your earlier post I noticed two things. Especially troubling is that you seem to be connecting a probe ground clip to one of the outputs. If that happened, you would be shorting the output to ground and it could be the kind of thing to damage that output. Did you really have that ground clip connected to the output?

The second thing is that the ground pad on the top right of the board looks like it doesn’t have much solder and might not be making a great connection. Could you try adding a bit of solder there and making sure it reflows over the whole ground pad?

-Claire

I don’t doubt that there are a lot of these boards out there and working. It is good to hear that there is no bigger issue. Considering that the OP and I are having the same issue I wonder if there is an easy way to kill this chip

The clip on the output is the oscilloscope ground. I do not believe that this would cause an issue. This is how I was verifying what the output signal is. Is there something with doing so that is bad? Also I am pretty sure I would have seen a spike on the power supply if I was shorting to ground, and I did not see one.

I will retouch the solder pad and try again.

I totally get what you were saying about shorting to ground, now. Thank you very much for spending the time to check out my pictures and help me see my screw up. I feel dumb for initially not seeing why this was the case. The trouble with a machinist learning electronics, I guess.

I appreciate your help and will definitely continue to preferentially buy from the team at Pololu.

It sounds like you might have resolved your issue. Were you able to get the driver working?

-Claire

100% and it works great.

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