AN1931D Freescale Semiconductor / Motorola, AN1931D Datasheet - Page 25

• Manufacturer Part Number: AN1931D
• Description: 3-Phase PM Synchronous Motor Vector Control
• Manufacturer: Freescale Semiconductor / Motorola

MOTOROLA
PWM
GENERATOR
OUTPUTS 0, 1
PWM COUNTER
PWM SYNC
PWM
PINS 0, 1
POWER
STAGE
VOLTAGE
TC2
COUNTER
TC2
OUTPUT
ADC
CONVERSION
ADC
ISR
the synchronization module TC2 (Quad Timer C, counter/timer 2). A high-true pulse occurs for each
reload of the PWM, regardless of the state of the LDOK bit. The intended purpose of TC2 is to provide
a user-selectable delay between the PWM SYNC signal and the updating of the ADC values. A
conversion process can be initiated by the SYNC input, which is an output of TC2. The time diagram
of the automatic synchronization between PWM and ADC is shown in
However, all three currents cannot be measured from one voltage shape. The PWM period II in
Figure 4-11
time. If the on-time is shorter than a critical time, the current can not be accurately measured. The
critical time is given by hardware configuration (transistor commutation times, response delays of the
processing electronics, etc.). Therefore, only two currents are measured and a third current is
calculated from the following equation:
Figure 4-9. Time Diagram of PWM and ADC Synchronization
shows a moment when the bottom transistor of Phase A is switched on for a very short
dead-time/2
Freescale Semiconductor, Inc.
3-Phase PM Synchronous Motor Vector Control
For More Information On This Product,
dead-time
t1
0
Go to: www.freescale.com
=
i
A
+
t2
i
B
+
i
C
dead-time/2
Figure
4-9.
dead-time
System Concept
(EQ 4-4.)
25