AMIS-30522 Datasheet, PDF (9/28 Pages) AMI SEMICONDUCTOR – Micro-stepping Motor Driver

AMIS-30522 Micro-stepping Motor Driver
Data Sheet
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 (Table 16: SPI Control Register 1).
Icoil
Duty Cycle
< 50%
Duty Cycle >50%
Actual value
Duty Cycle < 50%
Set value
T_PWM
Figure 7: Automatic Duty Cycle Adaption
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] (Table 28: SPI Control Parameter Overview
SM[2:0]) 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. Table 10 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. Table 9 lists the output current vs. the
translator position for this case.
Table 9: Square Translator Table for Uncompensated Half Step SM[2:0] = 101
Stepmode ( SM[2:0] )
% of Imax
101
Uncompensated Half Step
Coil x Coil y
0*
0
100
1
100
100
2
100
0
3
100
-100
4
0
-100
5
-100
-100
6
-100
0
7
-100
100
AMI Semiconductor – June 2007, M-20684-001
9
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