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DRV8711: Additional Decay Mode description

Allen Blaylock
Intellectual 310 points
Part Number: DRV8711


I am looking for some additional description of the decay mode as set in bits [10-8] DECMOD in the DECAY register on the DRV8711. 

In mode 001, Slow decay for increasing current, mixed decay for decreasing current, how is it determined if current is increasing or decreasing?

I can think of two possible ways to determine if current is increasing or decreasing:

  1. Is it based on where in the microstepping table we are? For example in table 4 from the DRV8711 datasheet from 0 to 90 degrees BOUT current is decreasing so mixed decay would always be used on B while AOUT is increasing so slow decay would be used on A? 
  2. Is it based on where we measure the current after TBLANK. For example if we measure the current to be below itrip we use slow decay and if we measure it above itrip we use mixed decay?

Thanks,

Allen

  • 0
    TI__Guru** 114905 points

    Hi Allen,

    Increasing current is based on the microstepping table. 

    When the absolute value of xOUT current in the table is greater than the previous step, it is considered increasing current.

    As an example using 1/8 step in Table 4, increasing current for AOUT is steps 2 through 9 and 18 through 25.

    For BOUT, increasing current is steps 10 through 17 and 26 through 1.