AMIS-30521 Datasheet, PDF (9/26 Pages) AMI SEMICONDUCTOR – Micro-stepping Motor Driver

AMIS-30521 Micro-stepping Motor Driver
Data Sheet
8.2.2. Automatic Duty Cycle Adaptation
Incase 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 14: 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 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] (Table 26: 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: Circular Translator Table lists
the output current versus 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: Square Translator Table for
Umcompensated Half StepSM[2:0] = 101 lists the output current versus the translator position for this case.
Table 9: Square Translator Table for Umcompensated Half StepSM[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-20683-001
9
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