Description
This A4988 microstepping bipolar stepper motor driver is ideal for Nema 17 bipolar stepper motor. It is suitable for 4 wire, 6 wire or 8 wires two-phase hybrid stepper motor if connected appropriately.
Features
- Simple step and direction control interface
- Five different step resolutions
- Adjustable current control lets you set the maximum current output with a potentiometer, which lets you use voltages above your stepper motor’s rated voltage to achieve higher step rates
- Intelligent chopping control that automatically selects the correct current decay mode (fast decay or slow decay)
- Over-temperature thermal shutdown, under-voltage lockout, and crossover-current protection
Specifications
- Minimum operating voltage: 8 V
- Maximum operating voltage: 35 V
- Continuous current per phase: 1 A (without a heat sink or forced air flow.)
- Maximum current per phase: 2 A (with additional cooling)
- Minimum logic voltage: 3 V
- Maximum logic voltage: 5.5 V
- Microstep resolutions: full, 1/2, 1/4, 1/8, and 1/16
Dimensions
Pinout and Connections
The A4988 driver has total 16 pins that interface it to the outside world. The connections are as follows:
Warning: A4988 uses low-ESR ceramic capacitors, which makes it susceptible to destructive LC voltage spikes, especially when using power leads longer than a few inches. Under the right conditions, these spikes can exceed the 35 V maximum voltage rating for the A4988 and permanently damage the board, even when the motor supply voltage is as low as 12 V. One way to protect the driver from such spikes is to put a large (at least 47 µF, preferably 100 µF) electrolytic capacitor across motor power (VMOT) and ground (GND) somewhere close to the board.
The A4988 driver has three microstep resolution selector inputs, MS1, MS2 & MS3 . By setting appropriate logic levels to these pins we can set the motors to one of the five step resolutions.
| MS1 | MS2 | MS3 | Microstep Resolution |
| Low | Low | Low | Full step |
| High | Low | Low | 1/2 step |
| Low | High | Low | 1/4 step |
| High | High | Low | 1/8 step |
| High | High | High | 1/16 step |
These three microstep selection pins are pulled LOW by internal pull-down resistors, so if we leave them disconnected, the motor will operate in full step mode.
If you need help controlling A4988 with Arduino or other microcontroller, you are welcome to contact us.
Setting the correct current
There’s a small trimmer potentiometer on the A4988 driver that can be used to set the current limit. You should set the current limit to be at or lower than the current rating of the motor.
You can set the current limit by measuring the voltage (Vref) on the “ref” pin (potentiometer).
- In the datasheet for your stepper motor find a rated current for stepper motor. In our case we are using NEMA 17 with rated current 250mA.
- Put the driver into full-step mode by leaving the three microstep selection pins disconnected.
- Hold the motor at a fixed position by not applying STEP pulses.
- Measure the voltage (Vref) on the metal trimmer pot itself while you adjust it.
- Adjust the Vref voltage using the formula: Vref = Current Limit x 0.4
For example, if your motor is rated for 250mA, you would adjust the reference voltage to 0.1V.
