71m6521fe Maxim Integrated Products, Inc., 71m6521fe Datasheet - Page 60

• Manufacturer Part Number: 71m6521fe
• Description: Energy Meter Ic
• Manufacturer: Maxim Integrated Products, Inc.

Measurement of absolute temperature uses the on-chip temperature sensor while applying the following formula:
In the above formula T is the temperature in °C, N(T) is the ADC count at temperature T, N
the sensitivity in LSB/°C as stated in the Electrical Specifications, and T
Example: At 25°C a temperature sensor value of 518,203,584 (N
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
formula, using –2220 for LSB/°C:
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 Coefficients: The internal voltage reference is calibrated during device manufacture.
The temperature coefficients TC1 and TC2 are given as constants that represent typical component behavior (in µV/°C and
Temperature Compensation: The CE provides the bandgap temperature to the MPU, which then may digitally compensate
the power outputs for the temperature dependence of VREF, using the CE register GAIN_ADJ. Since the band gap amplifier is
chopper-stabilized via the CHOP_EN bits, the most significant long-term drift mechanism in the voltage reference is removed.
The MPU, not the CE, is entirely in charge of providing temperature compensation. The MPU applies the following formula to
determine GAIN_ADJ (address 0x12). In this formula TEMP_X is the deviation from nominal or calibration temperature
expressed in multiples of 0.1°C:
In a production electricity meter, the 71M6521DE/FE is not the only component contributing to temperature dependency. A
whole range of components (e.g. current transformers, resistor dividers, power sources, filter capacitors) will contribute
temperature effects.
Page: 60 of 101
µV/°C
Since TC1 and TC2 are given in µV/°C and µV/°C
taken into account when transitioning to PPM/°C and PPM/°C
Since the output of the on-chip temperature sensor is accessible to the MPU, temperature-compensation mechanisms
with great flexibility are possible. MPU access to GAIN_ADJ permits a system-wide temperature correction over the
entire meter rather than local to the chip.
PPMC2 = 1374*TC2/1.195).
2
, respectively).
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
GAIN
_
ADJ
T
=
© 2005-2008 TERIDIAN Semiconductor Corporation
=
449.648.00
16385
Temperature Compensation
Temperature Measurement
512
+
TEMP
T
⋅
- 0
(
=
−
2220
518,203,58
(
N
2
_
, respectively, the value of the VREF voltage (1.195V) has to be
2
(
X
T
14
)
S
)
⋅
n
n
−
) is read by the ADC by a 71M6521FE in the 64-pin LQFP
PPMC
N
71M6521DE/71M6521FE
4
n
n
)
+
is +25°C.
2
+
. This means that PPMC = 26.84*TC1/1.195, and
25
+
T
n
C
TEMP
=
85
3 .
_
Energy Meter IC
°
C
X
2
23
n
2
is the ADC count at 25°C, S
⋅
PPMC
DATASHEET
2
JANUARY 2008
n
is
v1.0