Pwm Frequency Setting - Motorola M68HC08 Reference Manual

CAUTION:
6.5.7.2 Current Sampling Period
DRM028 — Rev 0
MOTOROLA
Freescale Semiconductor, Inc.
Range: <1,255>
The final PWM period is defined by setting SET_PER_PWM.
The PWM period [ s] is:
PWM period = PERIOD_PWM_US = SET_PER_PWM*2 (EQ 6-14.)
With default software setting (oscillator clock, etc.).
The final PWM frequency [Hz] is:
PWMfrequency
With default software setting.
Settings for some important PWM frequencies are listed in
Table 6-3. PWM Frequency Setting
SET_PER_PWM
16.0
25.0
32.0 (default)
128.0
Current measurement sampling period is synchronized with PWM.
Therefore, changing PWM frequency automatically changes the current
sampling period. This, apart from other things, effects the current
regulator. Therefore, after changing PWM frequency, changing (or
checking) current sampling period is strongly recommended.
Current sampling period should usually be changed in two cases:
1. When PWM frequency is changed
2. Motors with externally low electrical constant
If the motor electrical constant is lower than default current sampling
period of 128 s, the current regulator may not work properly.
User Guide
For More Information On This Product,
Go to: www.freescale.com
6
10
= ------------------------------------------------ -
2SET_PER_PWM
PWM Frequency
(FREQUENCY_PWM)
31.250 Hz
20.000 Hz
15.625 Hz
3.90625 Hz
User Guide
Tuning for Customer Motor
(EQ 6-15.)
Table 6-3.
PWM Period
(PERIOD_PWM_US)
32 s
50 s
64 s
256 s
Designer Reference Manual
157