71M6511 Maxim, 71M6511 Datasheet - Page 79

• Manufacturer Part Number: 71M6511
• Description: The 71M6511 and 71M6511H are highly integrated SoCs with an MPU core, RTC, flash, and LCD driver
• Manufacturer: Maxim

When applying the inverted coefficients, a curve (see Figure 30) will result that effectively neutralizes the original crystal
characteristics. The frequencies were calculated using the fit coefficients as follows:
The MPU Demo Code supplied with the TERIDIAN Demo Kits has a direct interface for these coefficients and it directly con-
trols the RTC_DEC_SEC or RTC_INC_SEC registers. The Demo Code uses the coefficients in the following form:
Note that the coefficients are scaled by 10, 100, and 1000 to provide more resolution. For our example case, the coefficients
would then become (after rounding, since the Demo Code accepts only integers):
Alternatively, the mains frequency may be used to stabilize or check the function of the RTC. For this purpose, the CE
provides a count of the zero crossings detected for the selected line voltage in the MAIN_EDGE_X address. This count is
equivalent to twice the line frequency, and can be used to synchronize and/or correct the RTC.
External Temperature Compensation
In a production electricity meter, the 71M6511 or 71M6511H is not the only component contributing to temperature de-
pendency. In fact, a whole range of components (e.g. current transformers, resistor dividers, power sources, filter capacitors)
will exhibit slight or pronounced temperature effects. Since the output of the on-chip temperature sensor is accessible to the
MPU, temperature-compensation mechanisms with great flexibility, i.e. beyond the capabilities implemented in the CE, are
possible.
Temperature Measurement
Temperature measurement can be implemented with the following steps:
Page: 79 of 98
1)
2)
3)
A Maxim Integrated Products Brand
Y_CAL = 109, Y_CALC = 12, Y_CALC2 = 7
At a known temperature T
Read the TEMP_X register at the known temperature. The obtained value should be <±0.1°C.
The temperature T (in °C) at any environment can be obtained by reading TEMP_X and applying the following
formula:
CORRECTION
T
f
=
=
T
f
N
nom
+
TEMP
⋅



1
+
10
10
_ X
a
(
6
ppm
+
32768.5
32768.4
32768.3
32768.2
32768.1
32767.9
32767.8
32767.7
32767.6
32767.5
T
32768
)
10
=
b
N
Y
6
-50
, read the TEMP_RAW register of the CE and write the value into TEMP_NOM.
+
_
10
T
© 2005–2010 Teridian Semiconductor Corporation
CAL
2
10
c
+
6
Figure 30: Crystal Compensation



T
⋅
-25
Y
_
100
CALC
+
crystal
curve fit
inverse curve
T
0
2
Single-Phase Energy Meter IC
⋅
Y
_
1000
CALC
71M6511/71M6511H
25
2
DATA SHEET
50
NOVEMBER 2010
V2.7