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
22,8 kHz
45,6 kHz
0
1
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
1
Single PWM frequency
Added jitter to PWM frequency
15.3.4. Motor Starting Phase
At motion start, the currents in the coils are directly switched from Iholdto Irunwith 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 tstab(see AC Table). The currents are then set to the hold values,
respectively Iholdx sin(TagPos)and Iholdx cos(TagPos) as illustrated below. A new positioning order can then be executed.
Ix
Iy
t
PC20051123.5
tstab
Figure 22: Motor Stopping Phase
AMI Semiconductor – June 2006, Rev 3.0
36
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