A3981 Datasheet, PDF (22/42 Pages) Allegro MicroSystems – Automotive, Programmable Stepper Driver

A3981
Automotive, Programmable Stepper Driver
In half step and in quarter step, the single phase active positions
are used to preserve symmetry. However, if the motor is required
to stop with a significant holding torque for any length of time
it is recommended that the 45° positions be used; those are Step
Angle Numbers 8, 24, 40, and 56, as used with full-step resolu-
tion.
The following table summarizes the Step Angle Numbers used
for the four resolutions available when using the STEP input to
I_A
24
8
I_B
40
56
Figure 5. Full-step phase diagram using STEP input
I_A
16
24
8
32
0
I_B
40
56
48
Figure 6. Half-step phase diagram using STEP input
20
24
28
32
I_A
16
12
8
4
0
I_B
36
60
40
44
48
56
52
Figure 7. Quarter-step phase diagram using STEP input
control the output of the A3981:
Mode
Full
Half
Quarter
Sixteenth
Step Angle Numbers used
8, 24, 40, 56
0, 8, 16, 24, 32, 40, 48, 56
0, 4, 8, 12, 16, 20, 24, 28, 32,
36, 40, 44, 48, 52, 56, 60
All
The microstep select inputs can be changed between each rising
edge of the STEP input. The only restriction is that the MSO and
MS1 logic inputs must comply with the set-up and hold timing
constraints. When the microstep resolution changes, the A3981
moves to the next available Step Angle Number on the next rising
edge of the STEP input. For example, if the microstep mode is
sixteenth and the present Step Angle Number is 59, then with the
direction forwards (increasing Step Angle Number), changing
to quarter step mode will cause the phase number to go to 60 on
the next rising edge of the STEP input. If instead the microstep
mode is changed to half step then the phase number will go to 0
on the next rising edge of the STEP input. If the microstep mode
is changed to full step then the phase number will go to 8 on the
next rising edge of the STEP input.
Control Through the Serial Interface
The A3981 provides the ability to directly control the motor
movement using only the serial interface. In fact, all features
of the A3981, except sleep mode, can be controlled through the
serial interface thus removing the requirement for individual
control inputs. This can reduce the interface requirement from
multiple I/O signals to a single four wire interface.
Motor movement is controlled using the serial interface by
increasing or decreasing the Step Angle Number. Note that the
maximum value of the Step Angle Number is 63 and the mini-
mum number is 0.Therefore, any increase or decrease in the
microstep number is performed using modulo 64 arithmetic. This
means that increasing a Step Angle Number of 63 by 1 will pro-
duce a Step Angle Number of 0. Increasing by two from 63 will
produce 1 and so on. Similarly in the reverse direction, decreasing
a Step Angle Number of 0 by 1 will produce a Step Angle Num-
ber of 63. Decreasing by two from 0 will produce 62 and so on.
The least significant six bits of the Run register, bits 0 to 5, are
the step change number, SC[5..0]. This number is a two’s comple-
ment number that is added to the Step Angle Number causing it
to increase or decrease. Two’s complement is the natural integer
number system for most microcontrollers. This allows standard
Allegro MicroSystems, Inc.
22
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com