4 improving data for feeding the curve fitter, 1 understanding the data and data format, An374 – Cirrus Logic AN374 User Manual
Page 25: 4m r, Eq. 22, Does not change, Code, Series, 1 t1 t0
AN374
AN374REV2
25
6.4 Improving Data for Feeding the Curve Fitter
This section demonstrates the use of a spreadsheet to manipulate the data collected in the previous section
to get a more accurate curve fit. The data is presented in a format compatible with the curve fitter software.
6.4.1 Understanding the Data and Data Format
The final data can be collected in a spreadsheet. An example of the spreadsheet is shown in Figure 16. Steps
are provided to the left to describe the process.
The NTC configuration section is shown in Figure 17. Values for Vref, Nbit and Ifs are internal parameters of
the IC that do not change. The beta and initial resistance at the initial temperature can be changed.
The NTC code can be generated using Equation 22. If temperature is specified in the system, then:
where
Temperature T1 and T0 are in degrees Kelvin
NTC Beta
4334 Vref
1.25
ENTER DIM VALUES (BwDim, RedDim), CURRENTS (I_bw, I_red)AND NTC TEMPERATURE (Tntc) in deg. C
NTC T0 °C
25 Nbit
8
NTC code IS COMPUTED FROM Tntc AND NTC PARAMETERS
NTC Rs at T0
100000 Ifs
8.00E-05
Series R
14000
іNTC PARAMETERS
enter
enter
љ
љ
BwDim
I_bw (A)
ї enter
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1
0.068
0.2
0.131
Tamb(room)
computed
ќ
enter
ќ
0.3
0.190
ї enter
5.00
0.042
0.078
0.110
0.138
0.161
0.180
0.196
0.207
0.216
0.221
0.09
0.16
0.23
0.28
0.33
0.37
0.40
0.42
0.44
0.45
0.4
0.246
15.00
0.044
0.083
0.116
0.145
0.170
0.190
0.206
0.218
0.227
0.233
0.09
0.17
0.24
0.30
0.35
0.39
0.42
0.45
0.46
0.48
0.5
0.297
25.00
0.046
0.087
0.122
0.153
0.179
0.200
0.217
0.230
0.239
0.245
0.09
0.18
0.25
0.31
0.36
0.41
0.44
0.47
0.49
0.50
0.6
0.344
45.00
0.049
0.091
0.128
0.160
0.187
0.210
0.228
0.241
0.251
0.257
0.10
0.19
0.26
0.33
0.38
0.43
0.46
0.49
0.51
0.53
0.7
0.386
65.00
0.051
0.096
0.135
0.168
0.197
0.220
0.239
0.253
0.264
0.270
0.10
0.20
0.28
0.34
0.40
0.45
0.49
0.52
0.54
0.55
0.8
0.425
85.00
0.053
0.101
0.142
0.177
0.207
0.231
0.251
0.266
0.277
0.284
0.11
0.21
0.29
0.36
0.42
0.47
0.51
0.54
0.57
0.58
0.9
0.460
1
0.490
Tamb(room)
enter
ќ
5.00
5.20
7.40
9.60
11.80
14.00
16.20
18.40
20.60
22.80
25.00
15.00
15.20
17.40
19.60
21.80
24.00
26.20
28.40
30.60
32.80
35.00
25.00
25.20
27.40
29.60
31.80
34.00
36.20
38.40
40.60
42.80
45.00
45.00
45.20
47.40
49.60
51.80
54.00
56.20
58.40
60.60
62.80
65.00
65.00
65.20
67.40
69.60
71.80
74.00
76.20
78.40
80.60
82.80
85.00
85.00
85.20
87.40
89.60
91.80
94.00
96.20
98.40
100.60
102.80
105.00
computed
ќ
13.5
15.2
17.0
19.0
21.2
23.6
26.1
28.9
31.9
35.1
22.5
25.0
27.6
30.5
33.6
36.9
40.5
44.2
48.2
52.4
35.4
38.8
42.5
46.3
50.4
54.7
59.2
64.0
68.9
73.9
74.4
79.7
85.1
90.6
96.2
102.0
107.7
113.6
119.5
125.3
Hight Temp Code Limit
185
125.9
131.7
137.5
143.3
149.0
154.6
160.0
165.4
170.7
175.8
Low Temp Code Limit
12
176.2
181.1
185.9
190.6
195.0
199.3
203.4
207.4
211.2
214.8
RedDim
Ra
Ɵo (String2/String1)
Tntc[C]
NTC code
I_red
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0
0.2
0.4
0.6
0.8
1
1.2
Ra
Ɵ
o
Dim
Current Ra
Ɵos Vs Dim
Tamb = 5C
Tamb=15C
Tamb = 25C
Tamb=45C
Tamb=65C
Tamb=85C
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0
0.2
0.4
0.6
0.8
1
1.2
Ou
tp
u
t Cu
rr
e
n
t (
m
A
)
Dim
Currents Vs Dim
I_BW
I_RED 5C
I_RED 15C
I_RED 25C
I_RED 45C
I_RED 65C
I_RED 85C
Step 1:
Enter NTC
Configuration
Step 4:
Enter Current Ratio
vs Dim and Temp
Step 5:
Enter Temperature or
NTC Resistance
Step 6:
Compute NTC Code
Step 3:
Enter Red Current vs
Dim and Temperature
Step 2:
Enter Blue
Current vs Dim
Figure 16. Example Spreadsheet Used to Collect Curve Fitting Data
NTC Beta
4334 Vref
1.25
NTC T0 °C
25 Nbit
8
NTC Rs at T0
100000 Ifs
8.00E-05
Series R
14000
Does Not Change
Figure 17. NTC Specification from Example Spreadsheet
NTC
CODE
4M
R
Series
R
T0
e
1
T1
-------
1
T0
-------
–
+
--------------------------------------------------------------------------
=
[Eq. 22]