#2134 Fails To Adjust VREF

Neither of my #2134 motor controllers will adjust the VREF.

The following readings have been confirmed with meter and scope: DIR is low, /SLEEP is high (5V), GND is at ground with driving Arduino Uno. STEP is a 50% duty cycle square wave at 20 milliseconds.

At first test VMOT was not active. DRV8834 datasheet suggests VMOT provides some power for chip functions.

Question: Would signals on DIR, or /SLEEP or STEP without VMOT cause chip failure?

The schematic on product page shows two VINT connections. I presume these are Vdd to '8834 chip. Question what is source for '8834 Vdd?

I will continue to check out these boards. But I have ordered boards #1182 that use the A4988 chip. That chip has specific pin for Vdd, while the DRV8834 does not specify a Vdd pin.


I am sorry you are having trouble adjusting VREF on both of your DRV8834 drivers. VMOT needs to be connected in order for the current limit to be set, and sending logic signals to !SLEEP, STEP, and DIR while VMOT is disconnected could damage the driver. However, it could also still be working fine, so you should try connecting power to VMOT before setting VREF.

The DRV8834 has an internal logic voltage supply, so it does not need an external VDD connection like the A4988.


Thanks your for your response. First a question and then a comment:

Since the A4988 boards include a Vdd pin, may we conclude these boards can receive logic signals without motor power present?

Some clarification may be appropriate in your product pages:

Your schematic on the #2134 product page notes a “logic power supply” source separate from the “motor power supply.” But nowhere on that page is the customer told that motor power should be present anytime logic signals are present.

Also note that the video showing how to set the VREF says VREF adjustment should be made before the motor is connected. This could be interpreted to mean the adjustment should be made before VMOT is activated.

I’m not suggesting the video should be updated. But the DRV product page(s) might be updated to remind customers to have VMOT present.

Thanks again for your response.

Bob LeDoux

Yes, since the A4988 has a separate pin, VDD, for logic power, it does not need to receive power at VMOT for doing something like adjusting VREF. The DRV8834 does not have a separate logic supply connection; it gets logic power from VMOT.

Thanks for your feedback about the DRV8834 product page; I have passed it on to the appropriate people to consider making an update.


Good and timely support–thank you.

Bob LeDoux