Motorola M68HC08 - Manual (Page 146)

User Guide
Designer Reference Manual DRM028 — Rev 0
146 User Guide MOTOROLA
Running state, or has a low start-up torque, DO decrease or increase
the PER_CMT_START_US value.
Table 6-2 shows typical setting
examples.
Must be:
PER_CMT_START_US<=PER_CMT_MAX_US/2
NOTE: Setting this constant is an empirical process. It is difficult to use a precise
formula, because there are many factors involved which are difficult to
obtain in the case of a real drive (motor and load mechanical inertia,
motor electromechanical constants, and sometimes also the motor
load). So they need to be set with a specific motor.
PER_CMT_START_US can be evaluated with PC master software
tuning file tuning_bldc.pmp.
Maximal commutation period limit [
µs]:
/* CAN_CHANGE_6_EXPER: */
#define PER_CMT_MAX_US 65536.0
Range: <0,65535*UNIT_PERIOD_T2_US>
Usually it is not recommended to change PER_CMT_MAX_US. The
change is only necessary if the commutation period at start-up is to
long.
Alignment to Start Increment of the regulators output [-]:
/* CAN_CHANGE_7_EXPER: */
#define START_INCR_OOUTREG 20.0
Range: <-128,127>
Table 6-2. Start-up Period
Motor Size
Typical
PER_CMT_START_
US
First-to-Seco
nd
Commutation
Step Period
Second-to-Thi
rd
Commutation
Step Period
Slow motor/high load and
motor mechanical inertia
8000.0 µs 8 ms 8–16 ms
Fast motor/high load and
motor mechanical inertia
2000.0
µs
2 ms 2–4 ms
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Freescale Semiconductor, Inc.
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