AN1627 Freescale Semiconductor / Motorola, AN1627 Datasheet - Page 17

• Manufacturer Part Number: AN1627
• Description: Low Cost High Efficiency Sensorless Drive for Brushless dc Motor Using MC68HC (7)05MC4
• Manufacturer: Freescale Semiconductor / Motorola

zero crossing signals (see Figure 6-1.). The values obtained from the tables are stored into internal
temporary variables in order to be ready when commutation is performed. The polarity edge sensitivity
(IEDG2) of the Timer Input Capture 2 Function is toggled (see Figure 5-3.) in order to detect the rising
or falling edge of the zero crossing signal. The edge polarity corresponds to the rotor position and the
actual commutation stage.
5.2.4.5
The Ramp routine calculates commutation period (Timer1) such that an “S” speed ramp is achieved. No
arithmetic division is required.
The formulas implemented are given below:
Const is a parameter which changes the slope of the Ramp
PeriodStart is the value of the commutation period when ramping is started.
PeriodStop is the value of the commutation period when ramping is finished.
5.2.5
5.2.5.1
Timer1 (A/D conversion) and Timer2 (commutation) are asynchronous software timers served by this
routine.
If the OC Interrupt is caused by Timer1 the A/D conversion of DC-Bus current is done here first in order
to be synchronized (within 4
the Over-current and Peak-current detection routines to make sure that it is within the limits. The flag for
the Current Controller is set. This flag causes the Current Controller subroutine to be called with new
data measured in this ISR.
On the other hand, if OC Interrupt is caused by Timer2, then the preset values (calculated in
Commutation subroutine) are put into the PWM registers (CtlA, CtlB) and the MUX command is output
too.
AN1627
REV 0.2
Acceleration:
Deceleration:
Ramp Subroutine
ISR - Interrupt Services Routines
Timer Output Compare Interrupt Service Routine
2500
2000
1500
1000
Speed [rpm]
500
0
0.000
Freescale Semiconductor, Inc.
2.000
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Period
s ) with the PWM signal (see Figure 5-5.). The obtained value goes through
Period




n
n


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4.000
time [s]


Figure 5-4.
Period
Period




n
n



--------------------------------------------------------------------------------------- -

--------------------------------------------------------------------------------------
Ramp
0.000
Period
Period




n
n


2.000
PeriodStart
PeriodStop

  h ex

  h ex
4.000


Speed [rpm]


Const
Const
time [s]

2500
2000
1500
1000
500
0





MOTOROLA
(EQ 5-1.)
(EQ 5-2.)
17