TMP007 datasheet(38/55 Pages) TI

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NORM

MEAS

Sensor

(mV)

Sensor

SampleNo

Sensor (mV)

a SampleNo b

TMP007

SBOS685C – APRIL 2014 – REVISED JULY 2015

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8.2.1.2 Detailed Design Procedure

Before attempting to calibrate the system, it is necessary to establish the stability of the system. Noise is a

measure of precision, which is the random deviation from the mean of the distribution. For a Gaussian (or

normal) distribution, the precision is typically characterized by the standard deviation (sensor noise),

σ.

8.2.1.2.1

Wide-Range Calibration

To begin calibration, select an object temperature (TOBJ) and a value for the die temperature (TDIE). With these

system temperatures stable, take a statistically significant number of samples of VSensor (results shown in register

00h).

in this example, 64 samples were taken. Do not use the object temperature readings given in register 03h; these

values are invalid before calibration.

To compensate for first order drift in system temperatures, it is often useful to normalize the data set. For this

purpose, for each temperature set, the sensor voltage data (given in register 00h) is normalized by first finding

the best fit line of the form shown in Equation 11:

(11)

The normalized data for each data set is then calculated as shown in Equation 12:

(12)

The normalized data, VSensor_norm, is centered on zero mean, and is first-order corrected for long-term drift. The

standard deviation for each data set is then calculated to estimate the sensor noise,

σ. Verify that the data are

limited by white noise and no other effects. For a sensor-noise-limited data set, vSENSOR σ is typically < 1 μV, and

preferably < 0.5

μV after first-order correction for drift, as described previously. If this condition is not satisfied,

then the calibration accuracy is limited by external system factors (for example, convection or conduction).

Repeat this process for each combination of TOBJ and TDIE for which the calibration is to be performed. The

normalized data are used only for evaluating the suitability of the data set for calibration, and not for the actual

calibration itself.

For calibration, the mean value, <VSENSOR>, is calculated for each combination of TOBJ and TDIE, as shown in

Table 12. Using the mean value minimizes error introduced by random noise. Based on the means, a set of

coefficients is generated based on a user-selected optimization criteria for Equation 7. Common criteria are

minimizing the maximum error, minimizing the average error, and so on. For a detailed discussion of optimization

methods, see SBOU142 — TMP007 Calibration Guide.

Table 12. Mean Values

TDIE

TOBJ

0°C

20°C

40°C

60°C

0°C

20°C

40°C

60°C

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