参数资料
型号: 71M6521FE-IGT/F
厂商: MAXIM INTEGRATED PRODUCTS INC
元件分类: 模拟信号调理
英文描述: SPECIALTY ANALOG CIRCUIT, QFP64
封装: LEAD FREE, LQFP-64
文件页数: 62/103页
文件大小: 1691K
代理商: 71M6521FE-IGT/F
71M6521DE/71M6521FE
Energy Meter IC
DATA SHEET
OCTOBER 2010
v1.1
2005-2010 Teridian Semiconductor Corporation
Page: 61 of 103
A Maxim Integrated Products Brand
19-5370; 10/10
Example: At 25°C a temperature sensor value of 518,203,584 (Nn) 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 Nn 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:
C
T
°
=
+
=
3
.
85
25
)
2220
(
512
4
518,203,58
-
0
449.648.00
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.
The temperature coefficients TC1 and TC2 are given as constants that represent typical component behavior (in V/°C and
V/°C
2, respectively).
Since TC1 and TC2 are given in V/°C and V/°C
2, respectively, the value of the VREF voltage (1.195V) has to be
taken into account when transitioning to PPM/°C and PPM/°C
2. This means that PPMC = 26.84*TC1/1.195, and
PPMC2 = 1374*TC2/1.195).
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:
23
2
14
2
_
2
_
16385
_
PPMC
X
TEMP
PPMC
X
TEMP
ADJ
GAIN
+
+
=
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.
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.
Temperature Compensation and Mains Frequency Stabilization for the RTC
The flexibility provided by the MPU allows for compensation of the RTC using the substrate temperature. To achieve this, the
crystal has to be characterized over temperature and the three coefficients Y_CAL, Y_CALC, and Y_CAL_C2 have to be
calculated. Provided the IC substrate temperatures tracks the crystal temperature the coefficients can be used in the MPU
firmware to trigger occasional corrections of the RTC seconds count, using the RTC_DEC_SEC or RTC_INC_SEC registers in
I/O RAM.
相关PDF资料
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