A4979 Datasheet, PDF (30/44 Pages) Allegro MicroSystems – The A4979 is a flexible microstepping motor driver with built-in translator for easy operation.

A4979
Microstepping Programmable Stepper Motor Driver
With Stall Detect and Short Circuit Protection
metrical about Step Angle Number 48 for phase A and about 32 A selection of the values and the corresponding phase current
for phase B. The forward and reverse profiles for each phase must table entries is shown in figure12. The full set of phase current
be the same.
table values is shown in the table below.
• The phase current must be zero at Step Angle Numbers 0 and 32
for phase A and Step Angle Numbers 16 and 48 for phase B.
Phase Current Table Programming Example
As an example of programming the phase current table, consider
the current profile shown in figure 11. This shows a profile where
the torque from each phase is required to be relatively higher
at the detent points, that is, the points where only one phase is
active. (This current profile does not relate to any specific motor,
it is only shown as an example.)
Figure 13 shows the required current for each phase at each
Step Angle Number as a percentage of the maximum phase
current, I_PMAX , defined above. The waveform conforms to the
required symmetry and zero crossing restrictions, so the profile
for phase A for Step Angle Numbers from 0 to 16 (outlined and
shaded) can be used to determine the phase table contents.
Step 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Value 10 20 25 28 29 30 31 32 35 40 50 58 60 62 63 63
PT 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
These 16 values are then loaded sequentially into the phase
current table through the Phase Table Load register of the serial
interface. Each value is then distributed to the appropriate Step
Angle Numbers as described above and as shown in table 4C in
the Phase Table Load Register section.
A representation of the final result is shown in figure 13. This
is the digitized version of the required current profile shown in
figure 13.
The first step is to digitize the profile into microsteps and the
percentage values into 6-bit numbers, as shown in figure 12.
At each of the one-sixteenth microsteps, identified by Step Angle
Number, the value of the phase current, as a percentage of the
maximum phase current, I_PMAX , is digitized to a 6-bit value from
0 to 63. The value 63 represents 100% of I_PMAX , 32 represents
32/63=50.8% and so on. The value at each Step Angle Number is
then assigned to its corresponding phase table values as follows:
PT n 1 DI_n
where DI_n represents the digitized value of the current at Step
Angle Number n.
Figure 13. Resulting example current profile
Allegro MicroSystems, Inc.
30
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com