A3981KLPTR-T Allegro Microsystems Inc, A3981KLPTR-T Datasheet - Page 39

• 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
opposite direction. In addition the phase B current at quarter-
step positions 3, 5, 11, and 13 also have the same magnitude as
that of phase A at quarter-step position 7, with a positive current
direction for steps 3 and 13 and a negative direction for steps 5
and 11. Similar symmetry can be applied to the phase B current at
quarter-step position 7, calculated above.
This means that only five discrete current magnitudes are
required, including 0% and 100%, in order to drive the stepper
motor to all 16 quarter-step positions. Using the same nomencla-
ture as figure A7, that is, I
is the quarter-step number from figure A6, table A1 shows where
each of the five magnitude values are used.
Figure A8 shows these values plotted as a current sequence
diagram. This figure is therefore the time-based equivalent of the
phase diagram in figure A6.
Figure A8. Phase current sequence for quarter step
Table A1. Quarter-Step Phase Current Magnitudes
Magnitude
-100%
-100%
100%
100%
-38%
-70%
-92%
-38%
-70%
-92%
100.
92%
70%
38%
92%
70%
38%
38.3
70.7
92.4
(%)
0.
0
0
I
I
B
A
12 13
I
I
I
I
A0
A1
A2
A3
–
14 15
Phase B
I
I
I
I
A7
A6
A5
A4
–
0
Pn
1
, where P is the phase, A or B, and n
I
I
I
I
A10
A11
A8
A9
–
2
3
I
I
I
I
A15
A14
A13
A12
4
–
5
I
I
I
I
6
–
B3
B2
B1
B0
7
Phase A
I
I
I
I
8
B4
B5
B6
B7
–
9
Automotive, Programmable Stepper Driver
10 11 12
I
I
I
I
B11
B10
–
B9
B8
I
I
I
I
B12
B13
B14
B15
–
Higher Microstep Resolution
The principles described above can easily be extended to higher
microstep resolutions. As the microstep resolution increases, it
becomes more apparent that the phase current sequences approxi-
mate ever closer to a sin and cosine function. Figure A9 shows
the measured phase current sequence of the A3981 running in
sixteenth-step mode. The phase current sequences for eighth-step
and sixteenth-step resolutions are shown in figures A10 and A11.
Most applications using small motors are limited to sixteenth-step
mode due to the mechanical precision of the motor. Larger, high-
precision stepper motors are sometimes driven at 32, 64, or even
up to 256 microsteps in some extreme cases.
Practical Implementation
A system to drive a stepper motor with microstep capability
requires sequencers, current reference generators, and current
controllers. Developing such a system from discrete components,
or even using a fast microcontroller, is a complex task. The
A3981 is one of several fully integrated stepper drivers that are
available with microstep resolutions, from simple half step to
sixteenth step and higher, using programmable current tables. All
aspects of the stepper control system are included in these single
chip solutions and many of them can be controlled by a simple
Step and Direction interface.
Figure A9. Measured sixteenth-step phase current sequence
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
39