Datasheet

71M6543F/71M6543G Data Sheet
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2 Hardware Description
2.1 Hardware Overview
The 71M6543 single-chip energy meter integrates all primary functional blocks required to implement a
solid-state electricity meter. Included on the chip are:
• An analog front-end (AFE) featuring a 22-bit second-order sigma-delta ADC
• An independent 32-bit digital computation engine (CE) to implement DSP functions
• An 8051-compatible microprocessor (MPU) which executes one instruction per clock cycle (80515)
• A precision voltage reference (VREF)
• A temperature sensor for digital temperature compensation of:
- Metrology (MPU)
- Automatic RTC in all power states
- MPU assisted RTC compensation
• LCD Driver
• RAM and Flash memory
• A real time clock (RTC)
• A variety of I/O pins
• A power failure interrupt
• A zero-crossing interrupt
• Selectable current sensor interfaces for locally-connected sensors as well as isolated sensors (i.e.,
using the 71M6xx3 companion IC with a shunt resistor sensor)
• Resistive Shunt and Current Transformers are supported
In order to implement a polyphase meter with or without neutral current sensing, one resistive shunt
current sensor may be connected directly (non-isolated) to the 71M6543 device, while up to three
additional current shunts are isolated using a companion 71M6xx3 isolated sensor IC. An inexpensive,
small size pulse transformer is used to electrically isolate the 71M6xx3 remote sensor from the 71M6543.
The 71M6543 performs digital communications bi-directionally with the 71M6xx3 and also provides power
to the 71M6xx3 through the isolating pulse transformer. Isolated (remote) shunt current sensors are
connected to the differential input of the 71M6xx3. The 71M6543 may also be used with Current
Transformers; in this case the 71M6xx3 isolated sensors are not required. Included on the 71M6xx3
companion isolator chip are:
• Digital isolation communications interface
• An analog front-end (AFE) featuring a 22-bit second-order sigma-delta ADC
• A precision voltage reference (VREF)
• A temperature sensor (for current-sensing digital temperature compensation)
• A fully differential shunt resistor sensor input
• A pre-amplifier to optimize shunt current sensor performance
• Isolated power circuitry obtains dc power from pulses sent by the 71M6543
In a typical application, the 32-bit compute engine (CE) of the 71M6543 sequentially processes the
samples from the voltage inputs on analog input pins and performs calculations to measure active energy
(Wh) and reactive energy (VARh), as well as A
2
h, and V
2
h for four-quadrant metering. These measurements
are then accessed by the MPU, processed further and output using the peripheral devices available to the
MPU.
In addition to advanced measurement functions, the real time clock (RTC) function allows the 71M6543 to
record time of use (TOU) metering information for multi-rate applications and to time-stamp tamper or other
events. An automatic RTC temperature compensation circuit operates in all power states including when the
MPU is halted, and continues to compensate using back-up battery power during power outages.
Measurements can be displayed on 3.3 V LCDs commonly used in low-temperature environments. The
integrated charge pump and temperature sensor can be used by the MPU to enhance 3.3 V LCD
performance at cold temperatures. The on-chip charge pump may also drive 5 V LCDs. Flexible mapping of
LCD display segments facilitates the integration of existing custom LCDs. Design trade-off between the