Demands for greater functionality, higher reliability, and lower cost have driven the development of the latest electronic energy-metering ICs. These devices, which include both system-on-a-chip (SoC) metering chips and general-purpose microcontrollers with metering-oriented peripherals, target a range of single-phase and three-phase electricity meter applications for residential or commercial use.
Functional integration is a key feature of the new energy-metering ICs, which aim to simplify the meter design, add new features, and reduce the overall meter-design cost. Some of the new chips also incorporate special features to prevent thieves from tampering with the meter. Requirements for energy efficiency are also in evidence in some of the metering devices, which boast intelligent power-management features aimed at minimizing the energy meter’s power consumption.
A summary of the capabilities offered by the new metering ICs is provided here, as well as functional block diagrams and application circuit examples based on these components. There are also links to other vendors who offer energy-metering ICs not covered this article.
Recent Introductions
In June, STMicroelectronics introduced a family of energy-metering ICs that incorporate all of the core circuitry necessary to implement a complete meter system without any other active component. The STPM1x family of single-phase energy-metering ICs measure active energy as pulse-frequency output and feature fast digital calibration, providing meter manufacturers with a cost-effective series of power-metering chips specifically designed for low-end metering applications.
Fully compliant with specifications for single-phase, class 0.5 static meters, the STPM1x ICs provide fast digital calibration at only one point over the whole current range. This capability allows a drastic reduction in manufacturing costs when compared to hardware calibration made using a resistor network. The mixed-signal ICs are designed for effective measurement of active energy in a power-line system using a wide variety of current sensors such as shunts, current transformers and Rogowski coils.
Analog blocks within the STPM1x include preamplifiers for signal conditioning, analog-to-digital converters (ADCs) and low-dropout voltage regulators to supply the circuitry. In the digital part of the device, the hardwired digital signal processor uses ripple-free computation algorithms to calculate the amount of consummated active energy, considerably reducing the meter’s calibration time.
In addition, the active energy is available through complementary pulsed outputs that enable an easier energy measurement while directly driving stepper-motor counters in low-end applications. The device is configured and calibrated through a serial port, which exploits the one-time programmable cells for permanently storing calibration parameters, preventing subsequent tampering. Offered in the TSSOP20 ECOPACK package, the STPM1x is priced at $1.40 each in quantities of 1000.
In July, Teridian Semiconductor unveiled the 71M6523 three-phase residential metering SoC. This device is designed to address the growing use of three-phase residential metering that is being driven by higher residential energy demand in developing economies. The 71M6523 delivers an anti-tamper neutral-current-measurement accuracy of 0.4%, allowing the detection of smaller amounts of energy theft. This degree of accuracy outperforms alternative solutions by a factor of two, according to the vendor.
Teridian’s Single Converter Technology and SoC approach also eliminate the need to isolate individual phases using multiple regulators and isolation devices, speeding development time, improving meter reliability and performance, and reducing overall system cost by as much as 40%.
“Until the introduction of Teridian’s 71M6523, meter manufacturers were forced into complex, less robust, less reliable meter designs cobbled together from many discrete components,” said Steve McClure, vice president of marketing for Teridian.
With this solution, energy-measurement accuracy is enhanced, the mean time between faults is increased, and EMI susceptibility and power consumption are reduced, says the vendor. The 71M6523 also offers advanced power management and tamper detection features. Battery backup mode functionality allows measurements to be displayed and updated, push-button wake-up from sleep mode, and communications and I/O.
Pricing for Teridian’s 71M6523 metering solution in 100,000-piece quantities is available upon request. Data sheets and evaluation kits are also available.
Another device offering tamper protection is austriamicrosystems’ AS8268, a single- phase, anti-tamper liquid crystal display (LCD) energy-metering IC. Introduced in April, the AS8268 offers an integrated SoC design for LCD display meters, and provides for secure program and data through its inclusion of high-performance flash memory on chip.Meter implementations based on the AS8268 require a minimum number of external components, improving meter reliability and reducing meter system cost.
The AS8268 incorporates all the required functional blocks for single-phase metering including a precision energy measurement front end, an 8-bit microcontroller, 32 kbytes of on-chip flash memory, a real-time clock, 96-segment LCD driver, 12 programmable multipurpose inputs/outputs for all possible customer-specified interfaces and display requirements, as well as an on-chip temperature sensor.
“The extremely reliable austriamicrosystems flash memory technology provided on-chip ensures program and data retention performance never before available to the metering industry in system-on-chip ICs,” says Matjaz Novak, marketing director of industry and medical for austriamicrosystems. “The flash memory has been designed and verified to operate over an extended operating temperature range of –40ºC to 125ºC.”
The AS8268 offers the option of using an external EEPROM of 2 kbytes to 32 kbytes for data retention, in conjunction with the fully programmable industry-standard 8-bit 8051-compatible microcontroller and 32 kbytes of on-chip flash memory. Two UARTs provide for external communication. A programmable energy LED pulse output can be displayed through one of the multipurpose input/outputs.
This precision output along with an on-chip pulse counter allows for the option of fast automatic digital calibration. An on-chip ±1.4-ppm real-time clock/calendar with two alarm registers and battery backup is available for complex tariff applications, with the option of added precision through the on-chip temperature sensor.
Active energy, mains voltage and mains current are calculated directly within the on-chip digital signal processor. Reactive power and apparent power can also be calculated by user-configurable application software. The AS8268 is available in a LQFP-64 pin package and is pin compatible with the currently available AS8218 and AS8228. Samples of the AS8268 are available.
In May, Texas Instruments announced sampling of its 16-MHz MSP430F47x4 ultralow-power microcontrollers (MCUs) for single- and multiphase meters. By integrating up to four individual 16-bit sigma-delta ADCs, a 32-bit x 32-bit hardware multiplier, a 160-segment LCD driver with contrast control, up to 60 kbytes of flash memory and a real-time clock, the F47x4 devices enable a 5:1 reduction in system components, according to the vendor.
With standby power consumption as low as 1.5 µA, a meter based on these devices allows utilities to reduce overall system power consumption. The F47x4 series MCUs feature several low-power modes, allowing the meter to sleep with almost no power drain between readings. An extremely fast wake-up brings the device to full clock speed within 6 µs. Together with a fast shutdown, this “instant-on” wake-up minimizes time spent in active mode.
The MSP430F47x4 series of MCUs are available for sampling. Unit pricing starts at $7.50 each in quantities of 1000.
Maxim Integrated Products also has introduced a 16-bit MCU targeting electricity metering and other industrial, medical or consumer applications that require a real-time clock and an LCD controller. Announced in July, the MAXQ3100 16-bit RISC microcontroller features an integrated temperature sensor and battery-backed, digitally trimmable real-time clock. The latter feature enables very accurate time keeping, which is critical for applications based on time-of-use events such as electricity tariffs.
An addition to the MAXQ microcontroller product line, the MAXQ3100 includes an LCD interface that supports up to 160 segments, a frequency-locked loop, two analog comparators and a digital temperature sensor. The MAXQ3100 has 16 kbytes of EEPROM program memory, 1 kbyte of data SRAM, a watchdog timer, two serial ports (USARTs) and three timers.
The dedicated RTC battery-backup pin lets a battery keep the RTC running when the controller's main power supply is absent. The built-in power-management circuit automatically detects and switches the RTC supply back to the main controller power supply whenever it is available. This intelligent power-management approach maximizes the RTC's battery life.
A MAXQ3100 evaluation kit (EV kit) is available that includes an on-board LCD and a JTAG interface board for communication with a PC. Its IDE includes a debugger, assembler/linker, a time-limited version of the IAR C-compiler and a simulator. The MAXQ3100 is available in an 80-pin MQFP. Pricing starts at $3.19 each in quantities of 1000.
Although not an energy-metering chip, Power Integrations’ previously introduced LinkSwitch power-supply chip gives meter designers an option for providing energy-efficient, tamper-resistant power to their electricity meters. In August, the company published a power-supply design idea (DI-141) based on its LinkSwitch-XT family.
The design idea offers an isolated power supply in flyback configuration that delivers 150 mA at 5 V, even under an intense external magnetic field. The use of an external magnetic field is said to be the most commonly used method of disabling meters without alerting existing anti-tamper measures.
Power Integrations’ LinkSwitch-XT family includes EcoSmart technology, which optimizes the efficient conversion of energy at different load levels. By replacing traditional linear power supplies with the LinkSwitch-XT based design, the 2 W of power used by power meters — the maximum amount recommended by the International Electrotechnical Commission — may be reduced to around 1 W while still providing the 750 mW of power required by the advanced meter electronics.
The DI-141 design idea, complete documentation for the LinkSwitch-XT family and a description of Power Integrations’ EcoSmart technology can be found at www.powerint.com.
For more information on the energy-metering components discussed in this article see:
STMicroelectronics
www.st.com
Teridian Semiconductor
www.teridian.com
austriamicrosystems
www.austriamicrosystems.com
Texas Instruments
www.ti.com
Maxim Integrated Products
www.maxim-ic.com
Power Integrations
www.powerint.com
Other vendors offering energy-metering ICs:
Analog Devices
Website provides information on vendor's energy-measurement ICs including the ADE7100 and ADE7500 energy meter SoC families, which were introduced in October 2006.
www.analog.com
Atmel
Application note presents the AVR465 single-phase power/energy meter with tamper detection, which is based on the AVR microcontroller.
www.atmel.com
Cirrus Logic
www.cirrus.com
Cypress Semiconductor
Press release announces the CY8C775X family of single-chip, single-phase, electric energy-metering ICs. Check with vendor for status of the CY8C775X.
www.cypress.com.
Freescale
Website includes a discussion of DSP-based energy-meter design using the DSP56F80x digital signal controller.
www.freescale.com
Microchip Technology
Website offers the MCP3909 three-phase energy meter reference design using PIC18F2520.
http://www.microchip.com
Renesas
http://america.renesas.com
For further reading on previously introduced energy-metering ICs, see:
Morrison, David, “ICs Ease Adoption of Electronic Energy Metering” Power Electronics Technology, February 2005.
Morrison, David, “Mixed-Signal ICs Build Smart Power Meters,” Power Electronics Technology, April 2005.