Calibrating A4988 via REF

Support Motor controllers/drivers and motors
1

Hi, I’m trying to setup the A4988 Stepper Motor Driver with Voltage regulator. I’d like to use REF pin to set the current limiting. It’s quickly referenced on the web site “Another way to set the current limit is to measure the voltage on the REF pin and to calculate the resulting current limit (the current sense resistors are 0.05Ω). See the A4988 datasheet for more information.” Since I’m by no means an EE, I have no idea how to figure it out from the datasheet.

The electrical specs for my motor hooked up as Bipolar in series are: Volts=8.4, Amps=1.4, Ohms=6, Impedence=27.2 mH, Holding torque=3.0 Nm. 0r 425 oz-in

Based on this, what is the procedure for setting up this motor using this process?

Thanks for any help anyone can offer.

I did view the getting started guide, but it uses the other method for calibration. Plus the diagrams are clear enough for a noob like myself. I’d prefer to see actual pictures and maybe a step-by-step video. :smiley: I’m connecting it to a Max32 from kellyware.com.

2

Hello.

The current limit can be calculated from the equation:

ITripMax = Vref / (8 * 0.05) = 2.5 * Vref

So if you have some target current limit, you should turn the pot until the Vref voltage is:

Vref = ITripMax / 2.5

I think your stepper motor is a little overpowered for the A4988 driver, at least in its stock configuration (you might be able to get around an amp per coil without overheating the driver). If you add a heat sink, you might be able to get closer to the stepper motor’s maximum current of 1.4 A per coil.

So, assuming you are not using a heat sink, I recommend starting out with a current limit under an amp. If you want to set the limit to 750 mA, you would set Vref to 0.75 / 2.5 = 0.3 V.

- Ben

3

Thanks, Ben. I did get some heatsinks for the chip, but I’ll start slow and see how hot they get before ramping up.