71M6521DE Datasheet, PDF (61/107 Pages) Teridian Semiconductor Corporation – Energy Meter IC

71M6521DE/DH/FE Data Sheet
Temperature Measurement
Measurement of absolute temperature uses the on-chip temperature sensor while 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.
Example: At 25°C a temperature sensor value of 518,203,584 (N_n) is read by the ADC by a 71M6521FE in the 64-pin
LQFP package. At an unknown temperature T the value 449.648.000 is read at (N(T)). The absolute temperature is
then determined by dividing both N_n and N(T) by 512 to account for the 9-bit shift of the ADC value and then inserting
the results into the above formula, using –2220 for LSB/°C:
T = ^{449.648.000 - 518,203,584} + 25C = 85.3°C
512 ⋅ (−2220)
It is recommended to base temperature measurements 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.
Temperature Compensation
Temperature Coefficients: The internal voltage reference is calibrated during device manufacture.
For the 71M6521DE/FE, the temperature coefficients TC1 and TC2 are given as constants that represent typical
component behavior (in µV/°C and µV/°C², respectively).
For the 71M6521DH, the temperature characteristics of the chip are measured during production and then stored in
the fuse registers TRIMBGA, TRIMBGB, TRIMT and TRIMM[2:0]. TC1 and TC2 can be derived from the fuses by
using the relations given in the Electrical Specifications section.
Since TC1 and TC2 are given in µV/°C and µV/°C², respectively, the value of the VREF voltage (1.195 V) 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 61) for the parts with regular accuracy 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%.
Similar considerations apply to the high-accuracy parts (see Table 62), where the error around the calibration
temperature should be considered constant at ±800 PPM, or ±0.08%.
Parameter
VREF(T) deviation from VNOM(T)
VREF(T ) − VNOM (T )
10 ⁶
VNOM (T )
max(T − 22 ,40)
Condition
Min
-40
Table 61: VREF Definition for the Regular Accuracy Parts
Typ
+40 PPM/ºC
Rev 2
Page: 61 of 107