VNH5019 Output doesn't go to 0V when PWM is 0V

Support Motor controllers/drivers and motors
1

Hi,

I’m new to motor drivers, and I think I might have a misconception about it. I’m trying to drive an actuator using the VNH5019 (in its non dual form). I want to apply a PWM signal and the output of the VNH5019 to go from 0 to the tension I put on VIN depending on the modulation width, in a more or less linear way.

I have:

  • VDD to 3.3V and GND to 0V
  • VIN to 5.5V and its respective GND to 0V connected to a power supply (VDD and VIN don’t share the same GND, and the GND is floating)
  • Finally I have connected INA to 3.3V, INB to 0V

I observe:

  • If I connect PWM to 3.3V, I have a spot-on tension of 5.5V between OUTB and OUTA
  • But If I connect PWM to 0V, I have a tension of 1.668V. If I increase VIN, this value increases also and it seems it is proportional
  • (If I apply a PWM signal, then I have a tension between 1.668V and 5.5V that seems to be proportional to the modulation width)

Is it normal? I was expecting that if I would connect PWM to 0V, I would have a tension of 0V between OUTB and OUTA.

Thanks for any information on that matter,

Raphael

2

Hello, Raphael.

Like other motor drivers, the output of the VNH5019 should vary approximately linearly between 0V and VIN based off of the duty cycle of the signal sent to the PWM pin. In reality, there might be some small negligible voltage (maybe measurable in the mV) across the outputs if the duty cycle of the PWM pin is zero, but it should definitely not be as high 1.6V.

In general for electronics like these, you should connect the grounds of your system together, and this could be the source of your issue. Also, it is not entirely clear what you mean when you say your ground is floating. Can you post a schematic diagram of your system?

-Jon

3

Hi Jon,

I won’t have the time to make schematic diagram of the system right now apart from what I describe with text, but I’ll do it later (end of the week).

I’ve tried to connect the two GNDs and it doesn’t change a single thing.

Anyway it looks like it’s connected on the VNH5019 schematic isn’t it? https://www.pololu.com/file/0J503/VNH5019_carrier_schematic.pdf

By floating I meant that I’m using a bench power supply for VIN and GND, and that I didn’t connect the Ground of the power supply to the Earth (doing so actually change things a bit but create a ground loop I think as I see more noise)

Thanks,

Raphael

4

Yes, the grounds are internally connected on the board. It was not clear how you were connecting ground from what you said in your first post, and if it was not properly connected, that could have been an easy solution, so that is why I pointed it out. Generally, for this type of electronics you do not need to connect GND on your power supply to Earth ground, so not connecting them would not usually be referred to as floating.

Can you use a multimeter to double check that you are connecting PWM to GND for your test and make sure everything is disconnected from the output of the driver? What do you measure when you separately measure the voltage across OUTA and GND and OUTB and GND? Are you using a multimeter to look at the voltages? Can you also post pictures that clearly show all of your connections? That should be faster than making a diagram and will likely show more anyway.

-Jon

5

Hi Jon,

Sorry for the late reply, didn’t have a time to work on a reply in the meantime.

What you say matches what I thought, and I discovered that if I just swap the signal to INA and INB the opposite led doesn’t light at all.

I guess that there was a problem with my board, or a problem with my cables. I’ve ordered the same chip but in its dual shield version and I’ll come back to this thread when I’ve solved those basic issues.

Thanks,

Raphael

6

Hi Jon,

So I received my dual board, soldered it and this time everything seems fine.

I think at some point I had a problem with the previous board, but I also made a mistake I think: When I was measuring, I didn’t use a load, and doing this for a short time on the new board actually shown the same exact voltage on the OUTA/OUTB output. If I put a small load of 100Ω I see the voltage difference go to 0.

Would the lack of loads on OUTA/OUTB could possibly fry the shield?

Thanks,

Raphael

7

I am glad your new motor driver seems to be working out for you!

In general, there is no reason that a brushed DC motor driver like the VNH5019 would be damaged by operating it without a load connected across its outputs.

-Jon