A3981KLPTR-T Allegro Microsystems Inc, A3981KLPTR-T Datasheet - Page 20

• Manufacturer Part Number: A3981KLPTR-T
• Description: AUTOMOTIVE PROGRAMMABLE STEPPER DRVR
• Manufacturer: Allegro Microsystems Inc

Specifications of A3981KLPTR-T

• Applications: Stepper Motor Driver, 2 Phase
• Number Of Outputs: 1
• Voltage - Load: 7 V ~ 28 V
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP (0.173", 4.40mm Width) Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

A3981
Motor Movement Control
The A3981 provides two independent methods to control the
movement of a stepper motor. The simpler is the Step and Direc-
tion method, which only requires two control signals to control
the stepper motor in either direction. The other method is through
the serial interface, which provides more flexible control capa-
bility. Both methods can be used together (although it is not
common), provided the timing restrictions of the STEP input in
relation to the STRn input are preserved.
Phase Table and Phase Diagram
The key to understanding both of the available control methods
lies in understanding the Phase Current table (table 7). This table
contains the relative phase current magnitude and direction for
each of the two motor phases at each microstep position. The
maximum resolution of the A3981 is one-sixteenth microstep.
That is 16 microsteps per full step. There are 4 full steps per elec-
trical cycle, so the phase current table has 64 microstep entries.
The entries are numbered from 0 to 63. This number represents
Figure 3. A3981 Phase Current table as a phase diagram; values shown
are referred to as the Step Angle Number
31
32
33
30
34
29
35
36
28
27
37
26
38
39
25
40
24
41
23
22
42
43
21
44
20
45
19
18
46 47 48 49 50
17
I
A
16
15
14
51
13
52
12
53
11
10
54
55
9
Application Information
Automotive, Programmable Stepper Driver
56
8
57
7
58
6
59
5
60
4
61
3
62
2
1
63
0
I
B
the phase angle within the full 360° electrical cycle and is called
the Step Angle Number. This is illustrated in figure 3.
Figure 5 shows the contents of the phase current table as a phase
diagram. The phase B current, I
plotted on horizontal axis and the phase A current, I
on the vertical axis. The resultant motor current at each microstep
is shown as numbered radial arrows. The number shown corre-
sponds to the one-sixteenth microstep Step Angle Number in the
phase current table.
Figure 4 shows an example of calculating the resultant motor
current magnitude and angle for step number 28. The target is to
have the magnitude of the resultant motor current be 100% at all
microstep positions. The relative phase currents from the phase
current table are:
Assuming a full scale (100%) current of 1A means that the two
phase currents are:
Figure 4. Calculation of resultant motor current
31
32
30
29
28
27
26
I
B28
25
= – 92.19%
24
I
I
I
I
A
B
A
B
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
= 37.50%
= –92.19%
= 0.3750 A
= -0.9219 A
B
, from the phase current table, is
157.9°

28
=
I
A
I
=37.5%
A28
A
I
, is plotted
B
20