Datasheet

71M6543F/71M6543G Data Sheet
v2 95
4.14 Crystal Oscillator
The oscillator of the 71M6543 drives a standard 32.768 kHz watch crystal. The oscillator has been
designed specifically to handle these crystals and is compatible with their high impedance and limited
power handling capability. The oscillator power dissipation is very low to maximize the lifetime of any
battery backup device attached to the VBAT_RTC pin.
Board layouts with minimum capacitance from XIN to XOUT require less battery current. Good layouts
have XIN and XOUT shielded from each other and also keep the XIN and XOUT traces short and away
from LCD and digital signals.
Since the oscillator is self-biasing, an external resistor must not be connected across the crystal.
4.15 Meter Calibration
Once the 71M6543 energy meter device has been installed in a meter system, it must be calibrated. A
complete calibration includes the following:
• Establishment of the reference temperature for factory calibration (e.g., typically 22 °C).
• Calibration of the metrology section, i.e., calibration for errors of the current sensors, voltage
dividers and signal conditioning components as well as of the internal reference voltage (VREF) at
the reference temperature (e.g., typically 22 °C).
• Calibration of the oscillator frequency using the RTCA_ADJ register (I/O RAM 0x2504).
The metrology section can be calibrated using the gain and phase adjustment factors accessible to the
CE. The gain adjustment is used to compensate for tolerances of components used for signal conditioning,
especially the resistive components. Phase adjustment is provided to compensate for phase shifts introduced
by the current sensors or by the effects of reactive power supplies.
Due to the flexibility of the MPU firmware, any calibration method, such as calibration based on energy, or
current and voltage can be implemented. It is also possible to implement segment-wise calibration
(depending on current range).
The 71M6543 supports common industry standard calibration techniques, such as single-point
(energy-only), multi-point (energy, Vrms, Irms), and auto-calibration.
Maxim provides a calibration spreadsheet file to facilitate the calibration process. Contact your Maxim
representative to obtain a copy of the latest calibration spreadsheet file for the 71M6543.