A4988 stepper driver

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Pololu stepper driver a4988
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Ready for shipping Weight: 0.005 kg
A4988 stepper driver
Kit includes
  • Pololu A4988 Stepper Driver
  • 1x16-pin breakaway 0.1" (2.54mm) male header
  • Heat Sink 6.3mm X 4.8mm w/ adhesive tape.

    Main caracteristics
  • 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
  • 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

    Power connections
    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).

    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, and MS3) enable selection from the five step resolutions according to the table below. MS1 and MS3 have internal 100k? pull-down resistors and MS2 has an internal 50k? 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 skip microsteps.
    Usual setting is sixteenth step, meaning all the jumper are set on the Ramps board.

    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 5? 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.
    To set the current limit measure the voltage on the “ref” pin and to calculate the resulting current limit (the current sense resistors are 0.05?). The ref pin voltage is accessible on a via that is circled on the bottom silkscreen of the circuit board. See the A4988 datasheet for more information.

    Power dissipation considerations The A4988 driver IC has a maximum current rating of 2 A per coil, but the chip by itself will overheat at lower currents. The actual current you can deliver depends on how well you can keep the stepper motor driver cool. The carrier’s printed circuit board is designed to draw heat out of the A4988 chip, but to supply more than approximately 1 A per coil, a heat sink is required.

    More information at Pololu and RepRap.
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