DRV8825 Datasheet, PDF (10/22 Pages) Texas Instruments – STEPPER MOTOR CONTROLLER IC

DRV8825
SLVSA73C – APRIL 2010 – REVISED MAY 2011
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The DRV8825 supports fast decay, slow decay and a mixed decay mode. Slow, fast, or mixed decay mode is
selected by the state of the DECAY pin - logic low selects slow decay, open selects mixed decay operation, and
logic high sets fast decay mode. The DECAY pin has both an internal pullup resistor of approximately 130 kΩ
and an internal pulldown resistor of approximately 80 kΩ. This sets the mixed decay mode if the pin is left open
or undriven.
Mixed decay mode begins as fast decay, but at a fixed period of time (75% of the PWM cycle) switches to slow
decay mode for the remainder of the fixed PWM period. This occurs only if the current through the winding is
decreasing (per the indexer step table); if the current is increasing, then slow decay is used.
Blanking Time
After the current is enabled in an H-bridge, the voltage on the xISEN pin is ignored for a fixed period of time
before enabling the current sense circuitry. This blanking time is fixed at 3.75 μs. Note that the blanking time also
sets the minimum on time of the PWM.
Microstepping Indexer
Built-in indexer logic in the DRV8825 allows a number of different stepping configurations. The MODE0 - MODE2
pins are used to configure the stepping format as shown in Table 2.
MODE2
0
0
0
0
1
1
1
1
MODE1
0
0
1
1
0
0
1
1
Table 2. Stepping Format
MODE0
0
1
0
1
0
1
0
1
STEP MODE
Full step (2-phase excitation) with 71% current
1/2 step (1-2 phase excitation)
1/4 step (W1-2 phase excitation)
8 microsteps / step
16 microsteps / step
32 microsteps / step
32 microsteps / step
32 microsteps / step
Table 3 shows the relative current and step directions for different settings of MODEx. 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 if the step mode is changed while stepping, the indexer will advance to the next valid state for the new
MODEx setting at the rising edge of STEP.
The home state is 45°. This state is entered at power-up or application of nRESET. This is shown in Table 3 by
the shaded cells.
1/32 STEP 1/16 STEP 1/8 STEP
1
1
1
2
3
2
4
5
3
2
6
7
4
8
9
5
3
10
11
6
Table 3. Relative Current and Step Directions
1/4 STEP 1/2 STEP
1
1
FULL
STEP
70%
2
WINDING
CURRENT
A
100%
100%
100%
99%
98%
97%
96%
94%
92%
90%
88%
WINDING
CURRENT
B
0%
5%
10%
15%
20%
24%
29%
34%
38%
43%
47%
ELECTRICAL
ANGLE
0
3
6
8
11
14
17
20
23
25
28
10
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