Pololu A5984 Stepper Motor Driver Carrier – Fixed 1A 5V / 660mA 3.3V (Blue Edition)

This is a Pololu carrier board for Allegro’s A5984 microstepping bipolar stepper motor driver. It offers eight different microstep resolutions (down to 1/32-step) and has over-current and over-temperature protection, and it features an adaptive decay algorithm that automatically optimizes the motor current waveform.

This version has a fixed current limit of 1A when VDD is 5V or 660mA when VDD is 3.3V and a four-layer PCB for better thermal performance. It can typically deliver phase currents up to the fixed limit of 1A without a heat sink or forced air flow. 

We are offering these carrier boards with support from Allegro Microsystems as an easy way to control bipolar stepper motors using their A5984 DMOS Microstepping Driver with Translator and Overcurrent Protection; we therefore recommend careful reading of the A5984 datasheet before using this product.

We offer this carrier with, or without, headers pre-soldered – please select an option before adding to cart. This product ships with all surface-mount components – including the A5984 driver IC – installed as shown in the product picture.

Warning: This product can get hot enough to burn you long before the chip overheats. Take care when handling this product and other components connected to it.

Features

• 8V to 40V supply voltage range (note: these are not recommended for use with 36V batteries, which can be well above nominal when fully charged)
• Simple step and direction control interface
• Eight different step resolutions:
  • Full-step with 100% current
  • Modified full-step (71% current)
  • 1/2-step with 100% current
  • Modified 1/2-step (circular)
  • 1/4-step
  • 1/8-step
  • 1/16-step
  • 1/32-step
• Adaptive Percent Fast Decay (APFD) current control algorithm, also known as QuietStep, automatically adjusts the amount of fast decay to optimize the motor current waveform
• Over-temperature thermal shutdown, over-current protection, and under-voltage lockout
• 2 oz copper PCB for improved heat dissipation; 2-layer (green PCB) and 4-layer (blue PCB) options available
• Exposed solderable ground pad below the driver IC on the bottom of the PCB
• Module size, pinout, and interface match those of our Pololu A4988 stepper motor driver carriers in most respects

Specifications

Minimum operating voltage	8V
Maximum operating voltage	40V
Continuous current per phase with VDD=5V	1A
Continuous current per phase with VDD=3.3V	660mA
Minimum logic voltage	2.5V
Maximum logic voltage	5.5V
Microstep resolutions	Full with 100% current full with 70% current non-circular 1/2, 1/2, 1/4, 1/8, 1/16, 1/32
Current limit	​Fixed 1A@5V / 660mA@3.3V
Reverse voltage protection?	N
Header pins	Not included
Size	0.6″ × 0.8″
Weight	1.2 g

Using the driver

Power connections

The driver requires a motor supply voltage of 8 V to 40 V (absolute max) to be connected across VMOT and GND. This supply should be capable of delivering the expected stepper motor current.

Motor connections

Four, six, and eight-wire stepper motors can be driven by the A5984 if they are properly connected; an FAQ answer on the Pololu website explains the proper wirings in detail.

Warning: Connecting or disconnecting a stepper motor while the driver is powered can destroy the driver. (More generally, rewiring anything while it is powered is asking for trouble.)

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 A5984 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, and MS3) enable selection from the eight step resolutions according to the table below. The driver defaults to full step with 100% current. 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 skip microsteps.

MS1	MS2	MS3	Microstep Resolution
Low	Low	Low	Full step with 100% current
Low	Low	High	Half step with 100% current (also called non-circular half step)
Low	High	Low	1/16 step
Low	High	High	1/32 step
High	Low	Low	Modified full step (71% current)
High	Low	High	Modified half step (circular)
High	High	Low	1/4 step
High	High	High	1/8 step

Control inputs and status outputs

The rising edge of 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 VDD or GND.

The chip has thee different inputs for controlling its power states: RESET, SLEEP, and ENABLE. The RESET pin (RST) is floating by default; this pin must be high to enable the driver (it can be connected to the adjacent SLEEP pin or directly to a logic “high” voltage between 2 V and 5.5 V, or it can be dynamically controlled from a digital output of an MCU). The default state of the SLEEP (SLP) and ENABLE (EN) pins is to enable the driver (the carrier board pulls SLEEP up to VDD and pulls ENABLE down to GND). See the datasheet for more details.

The A5984 also features an open-drain FAULT (nFAULT) output that drives low whenever the driver detects an over-current fault. The carrier board pulls this pin up to VDD, so no external pull-up is necessary on the FAULT pin. Bringing RESET or SLEEP low clears a latched fault.

Current limiting

To achieve high step rates, the motor supply is typically 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 5 Ω coil resistance, which would indicate a maximum motor supply of 5 V. Using such a motor with 9 V would allow higher step rates, but the current must actively be limited to under 1 A to prevent damage to the motor.

The A5984 supports such active current limiting, and this version of the carrier has a fixed current limit set with on-board resistors. The current limit is proportional to the logic voltage, VDD; for this board, it is about 1 A when VDD is 5 V or 660 mA when VDD is 3.3 V. More generally, the current limit in amps relates to VDD in volts as follows:

Current Limit = VDD / 5

You will typically want to choose a current limit that is at or below the current rating of your stepper motor.

Note: The coil current can be very different from the power supply current, so you should not expect the current measured at the power supply to match the current limit. The appropriate place to put your current meter is in series with one of your stepper motor coils. If the driver is in full-step 100% current or full-step 71% current modes, both coils will always be on and limited to 100% or 71% of the current limit setting, respectively. If your driver is in one of the microstepping modes, the current through the coils will change with each step, ranging from 0% to 100% of the set limit. See the A5984 datasheet for more information.

Power dissipation considerations

The A5984 has a maximum current rating of 2 A per coil, and it can supply up to around 1.2 A continuous per coil on this Blue Edition carrier board without overheating under typical conditions (i.e. operation in open space at room temperature), so this version that has a fixed current limit of 1 A or less will generally not need any special cooling to operate. However, additional cooling might be required for applications that limit heat dissipation, such as use in enclosed spaces or high ambient temperature conditions.

Warning: This product can get hot enough to burn you long before the chip overheats. Take care when handling this product and other components connected to it.

Please note that measuring the current draw at the power supply will generally not provide an accurate measure of the coil current. Since the input voltage to the driver can be significantly higher than the coil voltage, the measured current on the power supply can be quite a bit lower than the coil current (the driver and coil basically act like a switching step-down power supply). Also, if the supply voltage is very high compared to what the motor needs to achieve the set current, the duty cycle will be very low, which also leads to significant differences between average and RMS currents.

Additionally, please note that the coil current is a function of the set current limit, but it does not necessarily equal the current limit setting as the actual current through each coil changes with each microstep.

Resources

• Dimensions
• Schematic
• 3D Models
• Drill Guide
• A5984 datasheet
• Video: setting the current limit on Pololu stepper motor driver carriers
• Allegro product page for the A5984 DMOS Microstepping Driver

Package Contents

• 1x Pololu A5984 Stepper Motor Driver Carrier, Fixed 1A@5V / 660mA@3.3V, Blue Edition (with or without headers pre-soldered – select option before adding to cart)