DRV8434S: A few questions regarding step and decay mode

Hi Kawasaki-san,

Thanks for your post.

Yoshikazu Kawasaki said:

1. The sttepping is configured by MICROSTEP_MODE which is in one quadrant. For example, if MICSROSTEP_MODE=0110b, DRV8434S will increase/decrease current 16 steps in one quadrant, so it will have 16x4=64 steps in 360deg. Am I correct?

Yes 360 ° angle -or- one full sine wave in microstep mode. See below stepper current waveform for 1/16 microstep mode. One full sine wave of the current has 16 x 4 = 64 steps aka microsteps. The motor would've moved by 64 steps during this single sine wave cycle. 

Yoshikazu Kawasaki said:

2. The datasheet on page 11 says "The DRV8434S comes with smart tune decay modes". Would you please tell me how to find which decay mode is performed at a certain moment if there is? Would it be found by checking the DECAY[2:0] in CTRL2 control register?

After a power on or wake up from sleep the default setting for the CTRL2 register DECAY[2:0] will be 111b or Smart tune Ripple Control STRC decay mode. The DRV8434S stall detection features requires its decay mode to be set with STRC decay mode. For all other decay modes stall detection will not function. To confirm which decay mode was configured in the register CTRL2 DECAY[2:0] can be read at any time.

Yoshikazu Kawasaki said:

3. The table 7-7 on page 20 says "Mixed decay: 30% fast" or "Mixed decay: 60% fast" as DECREASING STEPS. Does it mean slow decay is 70% and fast decay is 30% if it is "Mixed decay: 30% fast"?

Yes correct. For Mixed 30 % fast, slow would be 70 % and fast would be 30 %. Likewise for Mixed 60 % fast, slow would be 40 % and fast would be 60 %. Thank you.

Regards, Murugavel