Tool/software:
Hi Team,
Can you walk me through how the choice between slow-decay, fast-decay and mixed-decay modes impacts torque ripple and heat dissipation at higher microstepping resolutions (e.g. 1/32 step), and what guidelines you recommend for selecting the optimal decay mode when driving up to 2.5 A continuous at 24–45 V
Hi Ernest,
Thank you for posting in this forum.
Can you walk me through how the choice between slow-decay, fast-decay and mixed-decay modes impacts torque ripple and heat dissipation at higher microstepping resolutions (e.g. 1/32 step), and what guidelines you recommend for selecting the optimal decay mode when driving up to 2.5 A continuous at 24–45 V
The decay settings impact the fidelity of the coil current waveforms, especially with microstepping modes where the current profile expected is sinusoidal. The decay mode defines how fast the current decays during current regulation chopping while the motor is running and BEMF is present. For decreasing current steps, for example in the 2nd and 4th quadrant of the sine wave without fast decay component the coil current would not decay fast enough to achieve the target current value. Fast decay means bridge reversal for a period of time which would mean higher energy dissipated in the driver which will impact efficiency. This is why we have mixed-decay.
See below snippet from page-13 of the datasheet. Mixed day is applied for decreasing currents or in other words 2nd and 4th quadrant of the current waveform, For the 1st and the 4th quadrant slow decay is used automatically. Slow decay is the most efficient because there is no bridge reversal. In summary for microstepping Mixed decay mode must be used. In this device 75 % of the tOFF is fast decay during mixed decay operation. For some motors and operating supply voltage range this may not be the best option.
The DRV8825 is one of our first generation integrated stepper drivers. Since then we've had several innovative integrated stepper drivers. For example the DRV8434. This device has Smart Tune decay modes which automatically determine the ideal ratio between the fast and slow decay operation based on operating voltage, speed, current and motor parameters. Smart Tune Ripple control decay mode offers lowers current ripple, hence lowest torque ripple. For newer designs we recommend considering the DRV8434 or similar family of stepper drivers. Thank you.
Regards, Murugavel
