71M6521DE Datasheet, PDF (9/101 Pages) Teridian Semiconductor Corporation – Energy Meter IC

71M6521DE/71M6521FE
Energy Meter IC
DATASHEET
JANUARY 2008
HARDWARE DESCRIPTION
Hardware Overview
The TERIDIAN 71M6521DE/FE single-chip energy meter integrates all primary functional blocks required to implement a solid-
state electricity meter. Included on chip are an analog front end (AFE), an independent digital computation engine (CE), an
8051-compatible microprocessor (MPU) which executes one instruction per clock cycle (80515), a voltage reference, a
temperature sensor, LCD drivers, RAM, Flash memory, a real time clock (RTC), and a variety of I/O pins. Various current
sensor technologies are supported including Current Transformers (CT), and Resistive Shunts.
In a typical application, the 32-bit compute engine (CE) of the 71M6521DE/FE sequentially processes the samples from the
voltage inputs on pins IA, VA, IB, VB and performs calculations to measure active energy (Wh), reactive energy (VARh), A²h,
and V²h 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 function allows the 71M6521DE/FE to record time of use
(TOU) metering information for multi-rate applications and to time-stamp tamper events. Measurements can be displayed on
3.3V LCD commonly used in low temperature environments. Flexible mapping of LCD display segments will facilitate
integration of existing custom LCD. Design trade-off between number of LCD segments vs. 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 meas-
urement and RTC accuracy, e.g. to meet the requirements of ANSI and IEC standards. Temperature dependent external com-
ponents such as crystal oscillator, current transformers (CTs), and their corresponding signal conditioning circuits can be
characterized and their correction factors can be programmed to produce electricity meters with exceptional accuracy over the
industrial temperature range.
One of the two internal UARTs is adapted to support an Infrared LED with internal drive and sense configuration, and can also
function as a standard UART. The optical output can be modulated at 38kHz. This flexibility makes it possible to implement
AMR meters with an IR interface. A block diagram of the IC is shown in Figure 1. A detailed description of various functional
blocks follows.
Analog Front End (AFE)
The AFE of the 71M6521DE/FE is comprised of an input multiplexer, a delta-sigma A/D converter and a voltage reference.
Input Multiplexer
The input multiplexer supports up to four input signals that are applied to pins IA, VA, IB and VB of the device. Additionally,
using the alternate mux selection, it has the ability to select temperature and the battery voltage. The multiplexer can be
operated in two modes:
• During a normal multiplexer cycle, the signals from the IA, IB, VA, and VB pins are selected.
• During the alternate multiplexer cycle, the temperature signal (TEMP) and the battery monitor are selected, along with
the signal sources shown in Table 1. To prevent unnecessary drainage on the battery, the battery monitor is enabled
only with the BME bit (0x2020[6]) in the I/O RAM.
The alternate mux cycles are usually performed infrequently (e.g. every second) by the MPU. In order to prevent disruption of
the voltage tracking PLL and voltage allpass networks, VA is not replaced in the ALT mux selections. Table 1 details the
regular and alternative MUX sequences. Missing samples due to an ALT multiplexer sequence are filled in by the CE.
v1.0
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