SLVA321A August   2011  – April 2021 DRV8811 , DRV8818 , DRV8821 , DRV8823 , DRV8823-Q1


  1.   Trademarks
  2. 1Introduction
    1. 1.1 Asynchronous Decay
    2. 1.2 Synchronous Decay
  3. 2Current Recirculation
    1. 2.1 Fast Decay
    2. 2.2 Slow Decay
    3. 2.3 Mixed Decay
      1. 2.3.1 Mixed Decay Modes
    4. 2.4 Smart Tune
  4. 3References
  5. 4Revision History

Mixed Decay Modes

There are two ways to handle mixed decay mode in stepper motor drivers: fixed and adjustable.

Fixed Mixed Decay Mode: Fixed mixed decay mode will time division multiplex a fast to slow decay ratio to a percentage that is preset into the core of the driver. For example 30% of the time on fast decay and 70% of remaining cycle time on slow decay.

Adjustable or Programmable Mixed Decay Mode: With device families such as the DRV88xx, an analog input is provided such that an analog voltage on the input encodes the mixed decay ratio. Whereas the DRV84xx family feature either digital input pins or register settings to select mixed decay ratios. Particular device datasheets provide specific details of setting the mixed decay ratio.

The required mixed decay ratio is determined by the application use case. Factors such as step rate, motor supply voltage, phase current setting, winding resistance and inductance determine the required mixed decay ratio to achieve the desired current ripple target. This process is called tuning. Tuning is very specific to the application use case.