Raspberry Pi 4 Model B wont boot with DRV8835 + S7V8F5

This is my first post to this forum but I hope someone can help me!
I have a brand new Raspberry Pi 4 Model B + DRV8835 dual motor driver + a voltage regulator S7V8F5.
The OS is Raspian and with the motor driver connectors unplugged the Pi boots just fine when powered only with the USB power source and the dual motor driver board not connected.

When i connect the dual motor driver board to the Pi I have been told that I should NOT connect BOTH USB C power and the 12V DC power connector as it will fry the Pi. So I am unplugging the USB C power source, and relying on the power to the dual motor driver board to power everything.

The trouble is, the Pi will not boot when powered via the dual motor driver board .
If I leave the dual motor driver board connected but disconnect the power lines to it, and use USB power, then the Pi boots.

Is my information on not connecting both power sources correct?

I’ve attached some photos of the overall connections, my 12V DC power plug and the way I’ve connected the regulator to the motor board.

I’m pretty new to this game so I hope someone is able to put me out of my misery and help with identifying the issue…

Thanks and best wishes to everyone in these difficult times!

Hell, Mark.

I noticed a few problems with your setup. First, your S7V8F5 regulator is attached backwards on your DRV8835 dual motor driver. As described on the product page, the motor driver board’s VOUT pin should connect to the regulator’s VIN pin, while the regulator’s VOUT pin should connect to the motor driver board’s 5V pin. Having it connected backwards means you were applying power to the regulator’s output instead of its input, which might have damaged it.

Second, neither the DRV8835 or the S7V8F5 are rated to handle 12V, so applying 12V with your power adapter also could have damaged them. Before proceeding, I recommend testing both your regulator and you driver with a lower voltage supply independently from both your Raspberry Pi and each other to see if they are still working.

If you need to operate with 12V, then I suggest using our Dual MAX14870 Motor Driver for Raspberry Pi along with either our D24V10F5 or our D24V22F5 regulator.

With either the DRV8835 or MAX14870 expansion boards, it is okay to independently power your Rapsberry Pi (such as through the USB C connector) and the driver, in which case you should not connect a regulator on your driver expansion board. If you do have a regulator connected on your driver expansion board so that you can power both your motors and your Raspberry Pi from one source, then you need to be careful never power to the Raspberry Pi through another source at the same time.

By the way, you might also want to check out this video about installing terminal blocks:

- Patrick

Hi Patrick,
Thanks for your comments and suggestions, I really appreciate them.
I’ll do some investigating this weekend.
Cheers Mark

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