3-Axis Bi-Polar Stepper Motor Driver Kit
User Manual
Version 2.0
Model: SideStep
Stepper Motor Microstepping Driver Specs:
- Chopper Current Driver
- .5 - 2.5 Amp Current Limiting
- Dual H-Bridge Configuration
- Full, Half, Quarter, & Eighth Microstepping Resolution
- 8V - 32V Supply
- Optional Integrated Charge Pump for 5V Logic Side
Description
The SideStep is a complete microstepping motor driver and control system with a built-in translator. It is designed to operate bipolar stepper motors in full-, half-, quarter-, and eighth-step modes, with output drive capability of 32 V and up to 2.5 A. This driver utilizes the Allegro A3977 chip which includes a fixed off-time current regulator that has the ability to operate in slow-, fast-, or mixed-decay modes. This current-decay control scheme results in reduced audible motor noise, increased step accuracy, and reduced power dissipation. The SideStep is one of the smallest stepper driver boards in its class, making it ideal for incorporating into robots and other industrial control equipment.
Bipolar Chopper Drivers
Bipolar chopper drivers are by far the most widely used drivers for industrial applications. Although they are typically more expensive to design, they offer more performance and increased efficiency. Bipolar chopper drivers use an extra set of switching transistors to eliminate the need for two power sources. Additionally, these drivers use a four transistor bridge with recirculating diodes and a sense resistor that maintains a feedback voltage proportional to the motor current. Motor windings, using a bipolar chopper driver, are energized to the full supply level by turning on one set (top and bottom) of the switching transistors. The sense resistor monitors the linear rise in current until the required level is reached. At this point the top switch opens and the current in the motor coil is maintained via the bottom switch and the diode. Current "decay" (loss over time) occurs until a preset position is reached and the process starts over. This "chopping" effect of the supply is what maintains the correct current voltage to the motor at all times.
Features
- Hardware or software selectable phase, enable, and direction signals
- Current limit adjustable by potentiometer
- Wide range of motor power (5-35 V)
- Power (for logic) indicator LED
- ±2.5 A, 35 V Output Rating
- Automatic Current Decay Mode Detection/Selection Mixed-, Fast-, and Slow-Decay Modes
- 3.0-5.5 V Logic Supply Voltage Range
- Home Output
- Synchronous Rectification for Low Power Dissipation
- Internal UVLO and Thermal-Shutdown Circuitry
- Crossover Current Protection
Flexible Design
The SideStep was designed with flexibility in mind with features including:
- Internal synchronous-rectification control circuitry is provided to improve power dissipation during PWM operation.
- Internal circuit protection includes thermal shutdown with hysteresis, under-voltage lockout (UVLO), and crossover-current protection. Special power-up sequencing is not required.
- The logic signals are brought out to a .1" pin header on one side, allowing for use of an IDC cable to connect your boards. Every other pin on the IDC header is connected to ground, which acts to shield the control signals from noise. Noise in a stepper control system can cause miss stepping, which can damage your equipment, cause injury, and ruin your work piece.
- The Vref signal and HOME signals are brought out to this header to allow advanced connections to control devices, such as a microcontroller which can adjust the driver's output current on-the-fly.
- The dip switch can be left uninstalled or removed and wired to a microcontroller to change the step resolution mid-motion for advanced speed ramping.
- The main control signals, STEP, DIRECTION, and ENABLE, as well as a GND connection, are brought out to WAGO type screw clamps for easy wiring to common devices, such as parallel port breakout boards.
- A two-stage, noise filtered, charge pump section is included. The first stage is regulated to 12 V, and has a header for a 12 V DC cooling fan. The second stage drops this 12 V down to 5 V which powers the driver's logic. This allows the logic supply to be driven from the same 12-24 V supply that the motor drive section is powered from. The logic supply has a power-on LED indicator.
- Alternately, the 12 V regulator can be left uninstalled or removed, allowing separate supplies for the logic and drive sections. The fan connector can be used for the power supply input.
- Both regulator sections can be left uninstalled or removed, to allow a single logic supply to be fed to the driver through the IDC pin header, such as from our PBX-1 breakout board with integrated charge pump.
- Additionally, the 5 V pin on the pinheader can be used to feed other boards from a single board, or to feed pull-up resistors for limit and home switches, provided that the current limits of the 7805 regulator are not exceeded.
- An 8-pin SIP resistor acts as the pull-ups for the logic signals. The eighth pin acts as a bridge in the event that your application requires reversed logic to the step and direction signals. Simply, cut off the necessary pin(s) from the SIP resistor before installing. A provision for an inline resistor and a decoupling capacitor has been included for noise filtering on the STEP signal.
- A solder jumper on the SR signal, which disables the drivers built-in synchronous rectification, allows for wiring external diodes for reduced heat dissipation. Wire one side of the jumper to +5V to disable synchronous rectification, or install the jumper to ground to enable this internally on the driver.
- A large ground plane exists for heat dissipation however, the layout of the components of this driver board allows for the use of a standard 1" square BGA heatsink. The board's large ground plane makes a heatsink unnecessary in many applications; however, use of a heatsink is recommended, especially when driving motors at higher than 1.5 amps per phase.
- An under-voltage lockout circuit protects the A3977 from potential shoot-through currents when the motor supply voltage is applied before the logic supply voltage. All outputs are disabled until the logic supply voltage is above 2.7V; the control logic is then able to correctly control the state of the outputs. Thermal protection circuitry turns off all the power outputs if the junction temperature exceeds 165°C. As with most integrated thermal shutdown circuits, this is intended only to protect the A3977 from failure due to excessive junction temperature and will not necessarily protect the IC from output short circuits. Normal operation is resumed when the junction temperature has decreased by about 15°C.
Setting Current Limit
- Measure the DC voltage between the Ref Pin and GND, and adjust the trimmer as follows: Vref = 1.6 * desired motor current.
- 2.5 A = Vref 4.0 V
- 2.0 A = Vref 3.2 V
- 1.5 A = Vref 2.4 V
- 1.0 A = Vref 1.6 V
- 0.5 A = Vref 0.8 V
WARNING: Do not exceed 4.0 V!
- Determine the step resolution you wish to use, and set the dip switches according to Figure 2.
- If driving your motors at more than 1.5Amp, install a BGA heatsink over the driver chip. Contact us if you need heatsinks.
- Apply power.
- Connect a voltmeter between the VREF signal and GND and adjust the current trimmer to the desired voltage determined above.
FIGURE 2:
WARNING: The SideStep has an optional on board voltage regulator section for supplying the logic side of the driver when NOT using one of our breakout boards or as a stand-alone stepper motor driver. JP1 must be removed when supplying the 5V logic voltage through the IDC cable header. Applying 5V through the IDC header, for example, when using on of our breakout boards, with this jumper installed will destroy your board and void your warranty!
WARNING: Never remove a connection to the stepper motor with power applied. There is a HIGH probability the A3977 IC will be damaged. The A3977 is rated for 35V DC max. The power supply voltage should be limited to ~32V DC to allow for back EMF generated by the stepper.
WARNING: If the motor is connected during this adjustment, excessive heating may occur. Most motors can NOT experience temperatures above 100°C. At these temperatures internal melting and seizure may occur. Short-term current overdrive will, in general, not harm most motors.
Motor Wiring
A chopper drive allows a stepper motor to maintain greater torque or force at higher speeds. The chopper drive uses Pulse Width Modulation and current sense feedback to regulate a constant current output of the drive transistors. The chopper gets its name from the technique of rapidly turning the output voltage on and off (chopping) to control motor current. Low impedance motor coils will deliver the best performance for a chopper driver. The chopper drivers main benefit is allowing you to overdrive your motors with a higher than rated supply voltage, which will charge the coils faster. So long as you do not exceed the breakdown voltage of the stepper motors coils, and do not exceed the rated voltage of the drives, you will benefit from faster acceleration and higher top end speeds, without harming your motors.
Microstepping electronically divides a full step into smaller steps by holding the stepper motors phases "in between" it's physical steps. For example, if a stepper motor provides 200 steps per revolution, then a eighth step micro-step driver would deliver 1600 steps per revolution. Micro-stepping increases step resolution and also reduces losses due to audible distortion and resonance. This results in a stronger, smoother operating drive. When microstepping, you must multiply the number of steps per unit by the micro-step resolution in the CNC control software. Microstepping effectively reduces the step increment of a motor at the cost of accuracy, because the electronic resolution does translate exactly to physical resolution. Therefore you should not rely on microstepping to increase your accuracy, but instead adjust your drive screw pitch when you need closer tolerances.
Installation Instructions
Control Software SetupThe SideStep is negative logic. The STEP, DIRECTION, and ENABLE lines should be inverted in your software. Please contact us if you need help configuring your software. Minimum pulse width for the step pulse is 5 uS. Maximum step frequency is 40 kHz. You may destroy your drivers if you try to exceed 40kHz. Most steppers torque really drop above 1 kHz at full step, or 8 kHz if you're using the eighth-step mode. |
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