
CTM
REFERENCE
MOTOROLA
9-7
PULSE WIDTH MODULATION SUBMODULE
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9
9.3.1
PWM frequency
The relationship between the PWM output frequency (f
PWMO
) and the MCU system clock
frequency (f
SYS
) is given by Equation 1.
[1]
where N
CLOCK
is the CPSM clock divide ratio (2 or 3) and N
COUNTER
is the PWMSM counter divide
ratio.
9.3.2
PWM pulse width
The minimum output pulse width (t
PWMIN
) and the MCU system clock frequency (f
SYS
) is given by
Equation 2.
[2]
Table 9-2
PWM pulse and frequency ranges (in Hz) using /3 option (16.78 MHz)
Mnimum
pulse width
Bits of resolution
9
16
15
14
13
12
11
10
8
7
6
5
4
3
2
1
0.179
μ
s
0.358
μ
s
0.715
μ
s
1.431
μ
s
2.861
μ
s
5.722
μ
s
11.44
μ
s
45.78
μ
s
/3
/6
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k 87.38k 174.8k 349.5k 699.1k
1398k
2796k
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k 87.38k 174.8k 349.5k 699.1k
1398k
/12
/24
/48
/96
/192
/768
21.33
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k 87.38k 174.8k 349.5k 699.1k
10.67
21.33
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k 87.38k 174.8k 349.5k
5.333
10.67
21.33
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k 87.38k 174.8k
2.667
5.333
10.67
21.33
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k 87.38k
1.333
2.667
5.333
10.67
21.33
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
21845
43.69k
0.333
0.667
1.333
2.667
5.333
10.67
21.33
42.67
85.33
170.7
341.3
682.7
1365
2731
5461
10923
f
PWMO
f
COUNTER
CLOCK
N
=
t
PWMIN
N
SYS
---f
=
F
.
Freescale Semiconductor, Inc.