Microcontroller and h-bridge choices for custom driver

hardware support
1

I’m currently developing a PCB to drive NEMA23 steppers with integrated encoders. Looking to make something that’s affordable but can drive fairly big motors. I’ve been looking at a lot of different drivers and microcontrollers and think I have settled on DRV8873 drivers with an RP2040.

For the motors, I was thinking about the 2 x VNH7070AS but they can only handle PWM up to 20KHz so now leaning towards the 2 x DRV8873 as don’t what audible noise. It has a lower current output but still enough for what I need and up to 100KHz PWM.

On the microcontroller side, thinking about an RP2040 as they’re super cheap, rock solid and I should be able to do 30KHz PWM with 12 bit resolution.

Anyone have any opinions about this setup, especially the VNH7070AS vs DRV8873? Thanks!

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Sounds pretty good unless you need current sensing as well, in which case the RP2040 is not ideal due to poor ADC.

It definitely sounds like the DRV driver is the one to go for :slight_smile:

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Thanks @runger! Was ignoring current sense as it’s not implemented for stepper motors at the moment, just BLDC motors…

void linkDriver(BLDCDriver *driver);

You think stepper current sense might be added in the future?

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It was actually added in the last (2.3.4) release! :slight_smile:

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@runger Ah, interesting. Back to the drawing board. Guess I could use an ESP32 or maybe an external ADC chip.

Is current sensing used at all in angle control mode?

Also, the datasheet for the DRV8873 says…

A current mirror allows the controller to monitor the load current. This mirror approximates the current through the high-side FETs, and does not require a high-power resistor for sensing the current.

…so assuming it wouldn’t work with SimpleFOC anyway as it’s high side current sensing? Maybe the VNH7070AS is the way to go after all as looks like it’s inline :thinking:

Thanks!

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It can be - the current sensing is used at the lowest level, to control the FOC loop, and works in combination with the higher level control for velocity or angle in the move loop…

I think maybe the benefits of the DRV chip outweigh the current sensing thing. You can always add external inline sensing if you want it.

Or you can add the high side sensing to SimpleFOC, that’s a matter of software. :slight_smile: I didn’t check the details of the current sensing implementation in the DRV8873, I should take a look.