Datasheet

PWM
RCx
PWM_ON
DECAY
VCC
BLANK
PWM_OFF
VBLANK
S
Q
Q
R
FAST_DECAY
0.21 × VCC
C
R
BLANK
ON
ITRIP
ON
PWM
ON
PWM
OFF
(t
OFF
)
Winding
Current
RCx
Voltage
ITRIP
0.6 × VCC
0.6 ×
VCC
0.21 × VCC
To other PWM
V
DECAY
FAST
(t
FD
)
SLOW
DECAY
V
BLANK
DRV8818
SLVSAX9C –SEPTEMBER 2011–REVISED NOVEMBER 2013 www.ti.com
Figure 3. PWM
Microstepping Indexer
Built-in indexer logic in the DRV8818 allows a number of different stepping configurations. The USM1 and USM0
pins are used to configure the stepping format as shown in the table below:
USM1 USM0 STEP MODE
0 0 Full step (2-phase excitation)
0 1 1/2 step (1-2 phase excitation)
1 0 1/4 step (W1-2 phase excitation)
1 1 Eight microsteps/steps
The following table shows the relative current and step directions for different settings of USM1 and USM0. At
each rising edge of the STEP input, the indexer travels to the next state in the table. The direction is shown with
the DIR pin high; if the DIR pin is low the sequence is reversed. Positive current is defined as xOUT1 = positive
with respect to xOUT2.
Note that the home state is 45 degrees. This state is entered at power-up or device reset. The HOMEn output
pin is driven low in this state. In all other states it is driven logic high.
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