AMIS-30522 Datasheet, PDF (9/29 Pages) AMI SEMICONDUCTOR – Micro-stepping Motor Driver

AMIS-30522
8.2.2. Automatic Duty Cycle Adaptation
In case the supply voltage is lower than 2*Bemf, then the duty cycle of the PWM is adapted automatically to >50% to maintain the
requested average current in the coils. This process is completely automatic and requires no additional parameters for operation.
The over-all current-ripple is divided by two if PWM frequency is doubled (see Table 16).
Icoil
Duty Cycle
< 50%
Duty Cycle >50%
Actual value
Duty Cycle < 50%
Set value
T_PWM
Figure 7: Automatic Duty Cycle Adaptation
t
PC20070604.2
8.3 Step Translator
8.3.1. Step Mode
The step translator provides the control of the motor by means of SPI register Stepmode: SM[2:0], SPI register DIRCNTRL, and
input pins DIR and NXT. It is translating consecutive steps in corresponding currents in both motor coils for a given step mode.
One out of seven possible stepping modes can be selected through SPI-bits SM[2:0] (see Table 28) After power-on or hard reset,
the coil-current translator is set to the default 1/32 micro-stepping at position ‘0’. Upon changing the step mode, the translator
jumps to position 0* of the corresponding stepping mode. When remaining in the same step mode, subsequent translator positions
are all in the same column and increased or decreased with 1. Error! Reference source not found. lists the output current vs. the
translator position.
As shown in Figure 8 the output current-pairs can be projected approximately on a circle in the (I_x,I_y) plane. There is, however, one
exception: uncompensated half step. In this step mode the currents are not regulated to a fraction of Imax but are in all intermediate
steps regulated at 100 percent. In the (I_x,I_y) plane the current-pairs are projected on a square. Error! Reference source not found.
lists the output current vs. the translator position for this case.
Table 9: Square Translator Table for Full Step and Uncompensated Half Step
Stepmode ( SM[2:0] )
MSP[6:0]
101
110
Uncompensated Half-Step
Full Step
000 0000
0*
-
001 0000
1
1
010 0000
2
-
011 0000
3
2
100 0000
4
-
101 0000
5
3
110 0000
6
-
111 0000
7
0*
% of Imax
Coil x
Coil y
0
100
100
100
0
-100
-100
-100
100
100
0
-100
-100
-100
0
100
Rev. 2 | Page 9 of 29 | www.onsemi.com