参数资料
型号: ST72141K2B3/XXX
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PDIP32
封装: 0.400 INCH, PLASTIC, SDIP-32
文件页数: 88/133页
文件大小: 2615K
代理商: ST72141K2B3/XXX
Obsolete
Product(s)
- Obsolete
Product(s)
ST72141K2
58/133
MOTOR CONTROLLER (Cont’d)
The Figure 36 gives the step ratio register value
(left axis) and the number of BEMF sampling dur-
ing one electrical step with the corresponding ac-
curacy on the measure (right axis) as a function of
the mechanical frequency.
For a given prescaler value (step ratio register) the
mechanical frequency can vary between two fixed
values shown on the graph as the segment ends.
In autoswitched mode, this register is automatical-
ly incremented/decremented when the step fre-
quency goes out of this segment.
At fcpu=4MHz, the range covered by the Step Ra-
tio mechanism goes from 2.39 to 235000 (pole
pair x rpm) with a minimum accuracy of 1.2% on
the step period.
To read the number of samples for Zn within one
step (right Y axis), select the mechanical frequen-
cy on the X axis and the sampling frequency curve
used for BEMF detection (PWM frequency or
measurment window frequency). For example, for
N.Frpm = 15,000 and a sampling frequency of
20kHz, there are approximately 10 samples in one
step and there is a 10% error rate on the measure-
ment.
Figure 36. Step Ratio Bits decoding and accuracy results and BEMF Sampling Rate
Step Ratio (Decimal)
N.Frpm
1
2.
3
9
4.
7
9
7.
1
8
9.
5
7
14
.4
19
.1
28
.7
38
.3
57
.4
76
.6
11
5
15
3
23
0
30
6
46
0
61
4
92
0
12
30
18
40
24
50
36
80
49
00
73
50
98
00
14
70
0
19
60
0
29
40
0
39
20
0
58
80
0
78
40
0
11
80
00
15
70
00
23
50
00
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
avg Zn ~ 7Fh ± 0.6%
100%
BEMF
samples
ΔZn/Zn
0%
10%
50%
1
2
4
10
200 Hz
20 kHz
avg Zn ~ FFh ± 0.4%
avg Zn ~ 7Fh ± 0.6%
avg Zn ~ FFh ± 0.4%
avg Zn ~ 55h ± 1.2%
Fn
3.Fn
Fn+1 = 2.Fn
3.Fn+1 = 6.Fn
Fstep = 6.N.Frpm = N.F / 10 N.F = 10.Fstep
N: Pole pair number
Fstep: Electrical step frequency
ST[3:0]
avg Zn ~ 55h ± 1.2%
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