AMIS-30623 Datasheet, PDF (36/67 Pages) AMI SEMICONDUCTOR – LIN Microstepping Motordriver

AMIS-30623 LIN Microstepping Motordriver
Data Sheet
15.3.2. PWM Regulation
In order to force a given current (determined by Irun or Ihold and the current position of the rotor) through the motor coil while ensuring
high energy transfer efficiency, a regulation based on PWM principle is used. The regulation loop performs a comparison of the sensed
output current to an internal reference, and features a digital regulation generating the PWM signal that drives the output switches. The
zoom over one micro-step in the figure above shows how the PWM circuit performs this regulation. To reduce the current ripple, a
higher PWM frequency should be selectable. The RAM register PWMfreq is used for this (Bit 0 in Data 8 of SetMotorParam).
Table 22: PWM Frequency Selection
PWMfreq
Applied PWM Frequency
0
22,8 kHz
1
45,6 kHz
15.3.3. PWM Jitter
To lower the power spectrum for the fundamental and higher harmonics of the PWM frequency, jitter can be added to the PWM clock.
The RAM register PWMJEn is used for this. (Bit 0 in Data 8 of SetStallParam). Readout with GetFullStatus (Bit 0 Data 8 IFR 2).
Table 23: PWM Jitter Selection
PWMJEn
Status
0
Single PWM frequency
1
Added jitter to PWM frequency
15.3.4. Motor Starting Phase
At motion start, the currents in the coils are directly switched from Ihold to Irun with a new sine/cosine ratio corresponding to the first
half (or micro) step of the motion.
15.3.5. Motor Stopping Phase
At the end of the deceleration phase, the currents are maintained in the coils at their actual DC level (hence keeping the sine/cosine
ratio between coils) during the stabilization time t_stab(see AC Table). The currents are then set to the hold values,
respectively Ihold x sin(TagPos) and Ihold x cos(TagPos) as illustrated below. A new positioning order can then be executed.
Ix
Iy
t
Figure 22: Motor Stopping Phase
t_stab
PC20051123.5
AMI Semiconductor – June 2006, Rev 3.0
36
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