AMIS-30532 Datasheet, PDF (12/29 Pages) ON Semiconductor – Micro-Stepping Motor Driver

AMIS--30532
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
Icoil
Duty Cycle
< 50%
Duty Cycle >50%
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 SPI
Control Parameter Overview PWMF).
Duty Cycle < 50%
Actual value
Set value
t
T_PWM
Figure 9. Automatic Duty Cycle Adaptation
Step Translator and 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 SPI Control Parameter
Overview). 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 versus
the translator position.
As shown in Figure 10 the output current--pairs can be
projected approximately on a circle in the (I_x, I_y) plane.
There are, however, two exceptions: uncompensated half
step and full step. In these step modes the currents are not
regulated to a fraction of I_max but are in all intermediate steps
regulated at 100%. In the (I_x, I_y) plane the current--pairs are
projected on a square. Table 9 lists the output current versus
the translator position for these cases.
Table 9. SQUARE TRANSLATOR TABLE FOR FULL STEP AND UNCOMPENSATED HALF STEP
Stepmode ( SM[2:0] )
101
110
% of I_max
MSP[6:0]
Uncompensated Half--Step
Full Step
Coil x
Coil y
000 0000
0*
--
0
100
001 0000
1
1
100
100
010 0000
2
--
100
0
011 0000
3
2
100
--100
100 0000
4
--
0
--100
101 0000
5
3
--100
--100
110 0000
6
--
--100
0
111 0000
7
0
--100
100
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