Rainbow Electronics 71M6542G - Manual (Page 11)

v1.1 © 2008–2011 Teridian Semiconductor Corporation 11
2 Hardware Description
2.1 Hardware Overview
The Teridian 71M6541D/F and 71M6542F single-chip energy meter ICs integrate all primary functional
blocks required to implement a solid-state residential 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:
- Metrology digital temperature compensation (MPU)
- Automatic RTC digital temperature compensation operational in all power states
• LCD drivers
• 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 71M6x01 companion IC with a shunt resistor sensor)
• Resistive Shunt and Current Transformers are supported
Resistive Shunts and Current Transformers (CT) current sensors are supported. Resistive shunt current
sensors may be connected directly to the 71M654x device or isolated using a companion 71M6x01
isolator IC in order to implement a variety of single-phase / split-phase (71M6541D/F) or two-phase
(71M6542F) metering configurations. An inexpensive, small size pulse transformer is used to isolate the
71M6x01 isolated sensor from the 71M654x. The 71M654x performs digital communications bi-
directionally with the 71M6x01 and also provides power to the 71M6x01 through the isolating pulse
transformer. Isolated (remote) shunt current sensors are connected to the differential input of the
71M6x01. Included on the 71M6x01 companion isolator chip are:
• Digital isolation communications interface
• An analog front end (AFE)
• A precision voltage reference (VREF)
• A temperature sensor (for 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 71M654x
In a typical application, the 32-bit compute engine (CE) of the 71M654x sequentially processes the samples
from the voltage inputs on analog input pins and from the external 71M6x01 isolated sensors 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 clock function allows the 71M6541D/F and 71M6542F
to record time-of-use (TOU) metering information for multi-rate applications and to time-stamp tamper or
other events. Measurements can be displayed on 3.3 V LCDs commonly used in low-temperature
environments. An on-chip charge pump is available to drive 5 V LCDs. Flexible mapping of LCD display
segments facilitate integration of existing custom LCDs. Design trade-off between the number of LCD
segments and DIO pins can be implemented in software to accommodate various requirements.
In addition to the temperature-trimmed ultra-precision voltage reference, the on-chip digital temperature
compensation mechanism includes a temperature sensor and associated controls for correction of unwanted
temperature effects on measurement and RTC accuracy, e.g., to meet the requirements of ANSI and IEC
standards. Temperature-dependent external components such as crystal oscillator, resistive shunts, current