A4980LP View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
MFG CO.
'A4980LP' PDF : 44 Pages View PDF
A4980
Automotive, Programmable Stepper Driver
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, IPn , where P is the phase, A or B, and n
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.
Table A1. Quarter-Step Phase Current Magnitudes
Magnitude
(%)
Phase B
Phase A
0.
38.3
70.7
92.4
100.
IA0
–
IA8
–
–
IB4
–
IB12
IA1
IA7
IA9 IA15 IB3
IB5
IB11 IB13
IA2
IA6 IA10 IA14 IB2
IB6 IB10 IB14
IA3
IA5 IA11 IA13 IB1
IB7
IB9 IB15
–
IA4
–
IA12 IB0
–
IB8
–
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 A4980 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
A4980 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.
IB
100%
92%
70%
38%
0
-38%
-70%
-92%
-100%
100%IA
92%
70%
38%
0
-38%
-70%
-92%
-100%
12 13 14 15 0 1 2 3 4 5 6 7 8 9 10 11 12
Figure A8. Phase current sequence for quarter step
Figure A9. Measured sixteenth-step phase current sequence
Allegro MicroSystems, Inc.
41
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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