A3977 Single Stepper Motor Driver Board


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This board is based on Allegro Microsystems A3977 Stepper Motor Driver IC.

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The A3977 is a complete microstepping motor driver, with built-in translator. It is designed to operate bipolar stepper motors in full-, half-, quarter-, and eighth-step modes, with output drive capability of 12 V and ±2.5 A. The A3977 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.


  • ±2.5 A per phase
  • 24 V output rating
  • Mixed, fast, and slow current decay modes
  • Synchronous rectification for low power dissipation
  • Internal UVLO and thermal shutdown circuitry
  • Crossover-current protection

Input Connections: 

Stepper Controller Board Input Pinout

A3977 Datasheet : 


Microstep Selection:

microstep selection

Current Setting:

To set the max current per phase place voltage meter from gnd to REF.  Then follow table below to get your desired current by adjusting the Cur pot.


Decay Mode:

You can also select the Decay mode with the PFD pot. When a STEP input signal commands a lower output current from the previous step, it switches the output current decay to either slow-, fast-, or mixed-decay depending on the voltage level at the PFD input. If the voltage at the PFD input is greater than 0.6 VDD then slow-decay mode is selected. If the voltage on the PFD input is less than 0.21 VDD then fast-decay mode is selected. Mixed decay is between these two levels. Use again your voltmeter to adjust the voltage with the pfd pot.


A3977 Schematics

Board Layout:

Board Layout


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