71M6531D_10 Datasheet, PDF (64/120 Pages) Teridian Semiconductor Corporation – Energy Meter IC

Data Sheet 71M6531D/F-71M6532D/F
FDS 6531/6532 005
3.3 Temperature Measurement
Measurement of absolute temperature uses the on-chip temperature sensor and applying the following
formula:
T
=
(N (T ) −
S_n
N_n)
+ T_n
In the above formula, T is the temperature in °C, N(T) is the ADC count at temperature T, N_n is the ADC
count at 25°C, S_n is the sensitivity in LSB/°C as stated in the Electrical Specifications and T_n is +25 °C.
It is recommended that temperature measurements be based on TEMP_RAW_X which is the sum of two
consecutive temperature readings, thus being higher by a factor of two than the raw sensor readings.
3.4 Temperature Compensation
3.4.1 Temperature Coefficients:
The internal voltage reference VREF is calibrated during device manufacture.
The temperature coefficient TC2 is given as a constant that represents typical component behavior (in
µV/°C²). TC1 (µV/°C) can be calculated for the individual chip from the contents of the TRIMT[7:0] I/O
RAM register. TC1 and TC2 allow compensation for variations of the reference voltage to within ± 40
PPM/°C.
Since TC1 and TC2 are given in µV/°C and µV/°C², respectively, the value of the VREF voltage
(1.195V) has to be taken into account when transitioning to PPM/°C and PPM/°C². This means
that PPMC = 26.84*TC1/1.195 and PPMC2 = 1374*TC2/1.195).
Close examination of the electrical specification (see Table 53) reveals that the achievable deviation is
not strictly ±40 PPM/°C over the whole temperature range: Only for temperatures for which T-22 > 40 (i.e.
T > 62°C) or for which T-22 < -40 (i.e. T < -18°C), the data sheet states ±40 PPM/°C. For temperatures
between -18°C and +62°C, the error should be considered constant at ±1,600 PPM, or ±0.16%.
Parameter
VREF(T) deviation from VNOM(T)
VREF(T ) − VNOM (T )
10 ⁶
VNOM (T )
max(T − 22 ,40)
Condition
Min
Typ
-40
+40 PPM/ºC
Table 53: VREF Definition for 6513H
Figure 31 shows this concept graphically. The “box” from -18°C to +62°C reflects the fact that it is imprac-
tical to measure the temperature coefficient of high-quality references at small temperature excursions.
For example, at +25°C, the expected error would be ±3°C * 40 PPM/°C, or just 0.012%.
The maximum deviation of ±2520 PPM (or 0.252%) is reached at the temperature extremes. If the refer-
ence voltage is used to measure both voltage and current, the identical errors of ±0.252% add up to a
maximum Wh registration error of ±0.504%.
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