DRV 8825 drive carrier phase current

We have been using the DRV 8825 for many years without problems. Nice product.

From datasheet on Pololu - DRV8825 Stepper Motor Driver Carrier, High Current
Continuous current per phase:1.5 A
Maximum current per phase:2.2A

The way to set the phase current is with the trimpot that sets both avref and bvref.
Trimpot in schematic (pololu.com)

The pins are as follows
from drv8825 guide: DRV8825 Stepper Motor Controller IC datasheet (Rev. F) (ti.com)

from the product page
Pololu - DRV8825 Stepper Motor Driver Carrier, High Current

We recently used changed the motor in our product from a 2.6A (0.9ohm and low L) to a 2.0A motor with 2.0A and much higher L. The driver is now getting hotter but we didn’t change anything. I woudl not expect it to get hot as 2.0A is very close to the 2.2A limit of the driver.

The VREF was measured and found to be 1.65V which means 3.2A per coil phase if this is correct. However, the datasheet shows 2.2A max which is closer to our 2.0A rating.

We are confused as we have a 2.0A motor that is causing it to get very hot where as the previous was 2.6A (lower inductance).

What is the current coming from the DRV 8825 carrier when it is configured this default way it ships?


We do not set the potentiometers on our stepper motor drivers, including the DRV8825, to a specific position before they ship. Additionally, it is possible to set the potentiometer in a position that configures a current limit beyond what our board and the driver can actually handle, so it is very important that you configure the current limit on every driver you receive to a value that is appropriate for your stepper motors. If your stepper motor is rated for higher than 1.5A per phase, we typically recommend setting the current limit to 1.5A (VREF = 0.75V) since that is the maximum current we found the driver could handle continuously in our testing (open, room temperature environment without additional heat sinks or other cooling). If VREF is 1.65V on your DRV8825 drivers, that is way too high!

In general, the driver can get quite hot (hot enough to burn you) during normal operation, but that by itself does not immediately indicate a problem with the driver. Could you try reducing your current limit to 1.5A (i.e. setting VREF to 0.75V) and seeing if you have any issues other than heat? If you continue to have problems, please describe what happens in detail and post some pictures of your board that show all of the connections in your setup.

- Patrick

So thank you for the prompt and concise answer.

So we do buy many hundreds of these drivers each year, for many years, the trimpot is always set to about 1.65V. Since the driver has a maximum value of 2.2A even with a heatsink, if the TI 8825 is running, it means it is producing closer to 3.3A by default if the pot is not adjusted.

Is there something wrong with this deduction?

I would advise against thinking of these drivers as having a “default” current limit. We do not specifically set the trimpots on the boards or check whether they are adjusted to a particular position, so you should not count on them always being set to a specific value, even if that is what you have seen in the past. For that reason, you should always check and set them yourself.

As described in the product page description under the “Power dissipation considerations” header, the DRV8825 driver IC has a maximum current rating of 2.5 A per coil, but the current sense resistors further limit the maximum current to 2.2 A. So, if the current limit is set higher than 2.2A, the board might not work as expected, or you might damage it.

However, there are other factors that can affect how much current your board is handling other than the current limit. Can you tell me how you are powering your stepper motor drivers and post more information about the motors you are using with them, like a datasheet or product page link for them?

- Patrick