71M6533 Datasheet, PDF (69/132 Pages) Teridian Semiconductor Corporation – Energy Meter IC

FDS_6533_6534_004
71M6533/G/H and 71M6534/H Data Sheet
correction coefficients PPM1 and PPMC2 per the formulae given in Section 6.4.15 VREF. See Section 3.5
Temperature Compensation for additional details.
The fuse TRIMBGB is non-zero for the high-accuracy parts and zero for the regular parts. Only partial trim
fuse information is available for the regular parts. The values for PPMC and PPMC2 that are used by the
CE to implement temperature compensation are calculated as follows:
• PPMC = TC1 * 22.46 = (52.46 - TRIMT) * 3.18 * 22.46 = (52.46 - TRIMT) * 71.423
• PPMC2 = TC2 * 1150.1 = –0.444 * 1150.1 = -510.6
The factor TRIMT used to calculate PPMC is derived from the trim fuse TRIMT[7:0].
3.3 Connecting 5 V Devices
All digital input pins of the 71M6533/71M6534 are compatible with external 5 V devices. I/O pins configured
as inputs do not require current-limiting resistors when they are connected to external 5 V devices.
3.4 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.
Example: At 25°C a temperature sensor value of 483,203,000 (N_n) is read by the ADC. At an unknown
temperature T the value 449.648.000 is read at (N(T)). We determine the absolute temperature by dividing
the difference of N_n and N(T) by 512 times the slope factor (-1180). After this, we add the 25 °C from the
reference measurement:
T = ^{449.648.000 - 483,203,000} + 25C = 80.5C
512 ⋅ (−1180)
The divisor 512 accounts for the 8-bit shift of the ADC value and for the factor of 2 introduced into the
measurement by the CE which adds two consecutive temperature readings.
3.5 Temperature Compensation
In a typical application, the CE compensates for the temperature dependency of the reference voltage
(see Section 4.1.1). System-wide temperature correction over the entire meter is possible by involving
the MPU. The thermal coefficients processed by the MPU may include the current sensors, the voltage
sensors, and other influences.
3.5.1 Temperature Coefficients
For the 71M6533 and 71M6534 (regular accuracy parts), the temperature coefficient TC2 is given as a
constant that represent typical component behavior (in µV/°C²). TC1 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.
For the high-accuracy parts, individualized coefficients TC1 and TC2 can be retrieved from the on-chip
fuses via TRIMBGA, TRIMBGB, TRIMM[2:0] (see Section 3.2 Distinction between 71M6533/71M6534 and
71M6533G/H/71M6534H Parts). For this part, TC1 and TC2 allow compensation for variations of the
reference voltage to within ±15 PPM/°C
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