Cirrus-logic AN374 Manual do Utilizador descarregar pdf (Página 25)

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

љљ

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)

computedќ

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

10.490

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

computedќ

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

RaƟo (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

RaƟo

Dim

Current RaƟos 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

Output Current (mA)

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

Series



-------

–













--------------------------------------------------------------------------

[Eq. 22]

1 2 ... 20 21 22 23 24 25 26 27 28 29 30 ... 34 35

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