71M6533/71M6534 Data Sheet
FDS_6533_6534_004
Only partial trim fuse information is available for non-H 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 confi-
gured 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:
(N(T) − Nn )
T =
+Tn
Sn
In the above formula T is the temperature in °C, N(T) is the ADC count at temperature T, Nn is the ADC
count at 25°C, Sn is the sensitivity in LSB/°C as stated in the Electrical Specifications, and Tn is +25 °C.
Example: At 25°C a temperature sensor value of 483,203,000 (Nn) 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 divid-
ing the difference of Nn and N(T) by 512 times the slope factor (-1180). After that, we add the 25C from
the reference measurement:
449.648.000 - 483,203,000
T =
+ 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. It is recommended that tem-
perature 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.
3.5 Temperature Compensation
In a typical application, the CE compensates for the temperature dependency of the reference voltage
(see Section 3.5.2). 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, 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 vol-
tage to within ±40 PPM/°C.
For the 71M6533H/71M6534H, 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
71M6533H/71M6534H Parts). For this part, TC1 and TC2 allow compensation for variations of the refer-
ence voltage to within ±15 PPM/°C
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