71M6513/71M6513H
3-Phase Energy Meter IC
A Maxim Integrated Products Brand
DATA SHEET
AUGUST 2011
Oscillator
The oscillator drives a standard 32.768kHz watch crystal (see Figure 9). Crystals of this type are accurate and do not require a
high current oscillator circuit. The oscillator in the 71M6513 Power Meter IC has been designed specifically to handle watch
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 pin.
71M651X
XIN
crystal
XOUT
Figure 9: Oscillator Circuit
The oscillator should be placed as close as possible to the IC, and vias should be avoided.
An external resistor across the crystal must not be added.
Real-Time Clock (RTC)
The RTC is driven directly by the crystal oscillator. In the absence of the 3.3V supply, the RTC is powered by the external
battery (VBAT pin). The RTC consists of a counter chain and output registers. The counter chain consists of seconds, minutes,
hours, day of week, day of month, month, and year. The RTC is capable of processing leap years. Each counter has its own
output register. Whenever the MPU reads the seconds register, all other output registers are automatically updated. Since the
RTC clock is not coherent to the MPU clock, the MPU must read the seconds register until two consecutive reads are the
same (requires either 2 or 3 reads). At this point, all RTC output registers will have the correct time. Regardless of the MPU
clock speed, RTC reads require one wait state.
The RTC interrupt must be enabled using the I/O RAM register EX_RTC (address 0x2002[1]). RTC time is set by writing to the
I/O RAM registers RTC_SEC, RTC_MIN, through RTC_YR. Each byte written to RTC must be delayed at least 3 CK32 cycles
from any previous byte written to RTC.
Two time correction bits, the I/O RAM registers RTC_DEC_SEC (0x201C[1]) and RTC_INC_SEC (0x201C[0]) are provided to
adjust the RTC time. A pulse on one of these bits causes the time to be decremented or incremented by an additional second
at the next update of the RTC_SEC register. Thus, if the crystal temperature coefficient is known, the MPU firmware can
integrate temperature and correct the RTC time as necessary as discussed in temperature compensation.
Comparators (V2, V3)
The 71M6513/6513H includes two programmable comparators that are connected to the V2 and V3 pins. The I/O RAM
register COMP_INT (0x2003[4:3]) allows the user to determine if comparators 2 and 3 will trigger an interrupt to the MPU. The
output of each comparator is available in the COMPSTAT register. VBIAS is used as the threshold, and built-in hysteresis
prevents each comparator from repeatedly responding to low-amplitude noise.
Comparators 2 and 3 can be used for early warning of power faults, or for monitoring of battery or other DC voltages. If they
are both selected to interrupt the MPU, their outputs will be XORed together. The voltage at V3 is also available to the ADC in
the AFE, but the comparator should not be used when V3 is used for analog measurements.
Comparator 1 is part of the power fault circuitry (see section V1 Pin) and cannot be programmed.
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