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).

Actual value

Duty Cycle

< 50%

Duty Cycle >50%

Duty Cycle < 50%

t

Icoil

Set value

PC20070604.2

Figure 7: Automatic Duty Cycle Adaption

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

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.

exception: uncompensated half step. In this step mode the currents are not regulated to a fraction of Imax but are in all intermediate

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

100

1

100

100

2

100

0

3

100

-100

4

0

-100

5

-100

-100

6

-100

0

7

-100

100

9

AMI Semiconductor

– June 2007, M-20684-001

www.amis.com