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Start-up period – Motorola M68HC08 User Manual

Page 146

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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.

For More Information On This Product,

Go to: www.freescale.com

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