參數(shù)資料
型號: 71M6521DE-IGT/F
廠商: MAXIM INTEGRATED PRODUCTS INC
元件分類: 模擬信號調理
英文描述: SPECIALTY ANALOG CIRCUIT, QFP64
封裝: LEAD FREE, LQFP-64
文件頁數(shù): 63/103頁
文件大小: 1691K
代理商: 71M6521DE-IGT/F
71M6521DE/71M6521FE
Energy Meter IC
DATA SHEET
OCTOBER 2010
Page: 62 of 103
2005-2010 Teridian Semiconductor Corporation
v1.1
A Maxim Integrated Products Brand
19-5370; 10/10
Example: Let us assume a crystal characterized by the measurements shown in Table 61:
Deviation from
Nominal
Temperature [°C]
Measured
Frequency [Hz]
Deviation from
Nominal
Frequency [PPM]
+50
32767.98
-0.61
+25
32768.28
8.545
0
32768.38
11.597
-25
32768.08
2.441
-50
32767.58
-12.817
Table 61: Frequency over Temperature
The values show that even at nominal temperature (the temperature at which the chip was calibrated for energy), the deviation
from the ideal crystal frequency is 11.6 PPM, resulting in about one second inaccuracy per day, i.e. more than some standards
allow. As Figure 30 shows, even a constant compensation would not bring much improvement, since the temperature
characteristics of the crystal are a mix of constant, linear, and quadratic effects.
32767.5
32767.6
32767.7
32767.8
32767.9
32768
32768.1
32768.2
32768.3
32768.4
32768.5
-50
-25
0
25
50
Figure 30: Crystal Frequency over Temperature
One method to correct the temperature characteristics of the crystal is to obtain coefficients from the curve in Figure 30 by
curve-fitting the PPM deviations. A fairly close curve fit is achieved with the coefficients a = 10.89, b = 0.122, and c = –0.00714
+
=
6
2
6
10
1
c
T
b
T
a
f
nom
When applying the inverted coefficients, a curve (see Figure 31) will result that effectively neutralizes the original crystal
characteristics.
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