71M6545 Datasheet, PDF (11/134 Pages) Maxim Integrated Products – Four-Quadrant Metering, Phase Metrology Processors Flash/RAM Size

PDS_6545_009
Data Sheet 71M6545/H
2 HARDWARE DESCRIPTION
2.1 Hardware Overview
The Teridian 71M6545/H single-chip Metrology Processor 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:
- Metrology digital temperature compensation (MPU)
- Automatic RTC digital temperature compensation operational in sleep mode (SLP)
• RAM and Flash memory
• A real time clock (RTC)
• A variety of I/O pins
• A power failure interrupt (CE code feature)
• A zero-crossing interrupt (CE code feature)
• 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 poly-phase meter with or without neutral current sensing, one resistive shunt
current sensor may be connected directly (non-isolated) to the 71M6545/H device, while 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 71M6545/H. The
71M6545/H 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 71M6545/H 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 71M6545/H
In a typical application, the 32-bit compute engine (CE) of the 71M6545/H 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 A²h, and V²h for four-quadrant metering. These measurements
are then accessed by the host processor via the SPI or by the on-chip MPU, to be processed further and
output using either the peripheral devices available to the on-chip MPU or by the host processor.
In addition to advanced measurement functions, the real time clock (RTC) function allows the 71M6545/H 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
(VBAT_RTC pin).
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 metrology and RTC accuracy (i.e., to meet the requirements of ANSI and IEC
standards). Temperature-dependent external components such as the crystal, current transformers
(CTs), Current Shunts and their corresponding signal conditioning circuits can be characterized and their
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