A4988 Stepper Motor Driver Carrier
 

The A4988 stepper motor driver carrier is a breakout board for Allegro’s easy-to-use A4988 microstepping bipolar stepper motor driver.
The driver features adjustable current limiting, overcurrent protection, and five different microstep resolutions.
It operates from 8 – 35 V and can deliver up to 2 A per coil with sufficient additional cooling
(it can deliver up to approximately 1 A per phase without a heat sink or forced air flow).
 

This product is a carrier board or breakout board for Allegro’s A4988 DMOS Microstepping
Driver with Translator and Overcurrent Protection; we therefore
recommend careful reading of the A4988 datasheet (380k pdf) before using this product.
This stepper motor driver lets you control one bipolar stepper motor at up to 2 A output current per coil
(see the Power Dissipation Considerations section below for more information).
 

This product ships with all surface-mount
components—including the A4988 driver IC—installed as shown in the product picture.

The Black Edition A4988 stepper motor driver carrier is available with approximately 20% better performance.
Except for thermal characteristics, the Black Edition and this (green) board are interchangeable.
We also sell a larger version of the A4988 carrier that has reverse power
protection on the main power input and built-in 5 V and 3.3 V voltage regulators that eliminate the
need for separate logic and motor supplies.
 

מאפיינים

• Simple step and direction control interface
• Five different step resolutions: full-step, half-step, quarter-step, eighth-step, and sixteenth-step
• 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
• Short-to-ground and shorted-load protection
   

The driver requires a logic supply voltage (3 – 5.5 V) to be connected across the VDD and GND pins and a motor supply voltage of (8 – 35 V) to be connected across VMOT and GND. These supplies should have appropriate decoupling capacitors close to the board, and they should be capable of delivering the expected currents (peaks up to 4 A for the motor supply).
 

Motor connections

Four, six, and eight-wire stepper motors can be driven by the A4988 if they are properly connected; a FAQ answer explains the proper wirings in detail.
 

Step (and microstep) size

Stepper motors typically have a step size specification (e.g. 1.8° or 200 steps per revolution), which applies to full steps.
A microstepping driver such as the A4988 allows higher resolutions by allowing intermediate step locations,
which are achieved by energizing the coils with intermediate current levels.
For instance, driving a motor in quarter-step mode will give the 200-step-per-revolution
motor 800 microsteps per revolution by using four different current levels.

The resolution (step size) selector inputs (MS1, MS2, MS3) enable selection from the five step resolutions
according to the table below.
MS1 and MS3 have internal 100kΩ pull-down resistors and MS2 has an internal 50kΩ
pull-down resistor, so leaving these three microstep selection pins disconnected results in full-step mode.

For the microstep modes to function correctly, the current limit must be set low enough (see below) so that current limiting gets engaged.
Otherwise, the intermediate current levels will not be correctly maintained, and the motor will effectively operate in a full-step mode.
 

Control inputs

Each pulse to the STEP input corresponds to one microstep of the stepper motor in the direction selected by the DIR pin.
Note that the STEP and DIR pins are not pulled to any particular voltage internally,
so you should not leave either of these pins floating in your application.
If you just want rotation in a single direction,
you can tie DIR directly to VCC or GND.
The chip has three different inputs for controlling its many power states: RST, SLP, and EN.
For details about these power states, see the datasheet. Please note that the RST pin is floating;
if you are not using the pin, you can connect it to the adjacent SLP pin on the PCB.

Current limiting

To achieve high step rates, the motor supply is typically much higher than would
be permissible without active current limiting.
For instance, a typical stepper motor might have a maximum
current rating of 1 A with a 5Ω coil resistance, which would indicate a maximum motor supply of 5 V.
Using such a motor with 12 V would allow higher step rates, but the current must actively be limited to under 1 A to prevent damage to the motor.

The A4988 supports such active current limiting, and the trimmer potentiometer on the board can be used to set the current limit.
One way to set the current limit is to put the driver into full-step mode and
to measure the current running through a single motor coil without clocking the STEP input.
The measured current will be 0.7 times the current limit
(since both coils are always on and limited to 70% of the current limit setting in full-step mode).
Please note that changing the logic voltage, Vdd, to a different value will change the current limit setting since
the voltage on the “ref” pin is a function of Vdd.

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).
The ref pin voltage is accessible on a via that is circled on the bottom silkscreen of the circuit board.
The current limit relates to the reference voltage as follows:

Current Limit = VREF * 2.5

So, for example, if the reference voltage is 0.3 V, the current limit is 0.75 A. As mentioned above, in full step mode,
the current through the coils is limited to 70% of the current limit,
so to get a full-step coil current of 1 A, the current limit should be 1 A/0.7=1.4 A,
which corresponds to a VREF of 1.4 A/2.5=0.56 V. See the A4988 datasheet for more information.