TIDA-00830
24V Stepper Motor Design with AutoTune™
TI Reference Design
3
much fast decay is needed. An example of a motor tuning that utilizes too much fast decay at some
steps is shown in
Figure 3
below. This results in a large amount of power supply decay current ripple.
Figure 3.
Supply Current Ripple Using Fast / Slow Decay
Figure 4.
Supply Current Ripple Using
AutoTune
To avoid this issue, the DRV8880 has an adaptive decay mode called AutoTune
™ that automatically
adjusts the amount of fast decay inserted during t
OFF
to best suit the motor characteristics and load
conditions at any instance in time. An example of AutoTune working is shown in
Figure 4
above.
4. AutoTune
By utilizing AutoTune
™, the user can simply connect a motor and the driver will begin spinning it in the
most effective way possible without requiring any other parameter tuning. AutoTune operates by
actively calculating and adjusting the current decay. Each drive cycle has a mandatory t
BLANK
interval to
drive the motor. Once the t
BLANK
interval has elapsed, the device can continue with the remainder of
the t
DRIVE
interval if it has not hit the current limit I
TRIP
, or stop driving and begin decaying current if the
current limit has been reached based on whichever decay setting AutoTune
™ chooses.
t
BLA NK
t
DRIVE
t
SLOW
t
OFF
t
FA ST
I
TRIP
In
c
re
a
s
in
g
P
h
a
s
e
C
u
rr
e
n
t
(A
)
Figure 5.
Mixed Decay Timing Profile
If AutoTune
™ selects a mixed decay mode the driver actively inserts different percentages of fast
decay during each t
OFF
interval, and effectively lowers the current ripple while driving the motor in the
most efficient way possible. An example of a mixed decay current profile is shown in
Figure 5
above.
Since the driver is allowed to actively change the decay pattern it can also easily adapt to changing
motor operation factors without requiring the user to retune any of the driver parameters. This is an
especially relevant feature in applications where the motor will be run for long periods of time and aging
effects need to be considered.
