Single/multiphase energy-measurement IC eases smart-grid transition for utility meters

Austin, Texas—look out, you spinning-disk utility meters out there: your days of ruling the power line are coming to a close. That's the impression you'll get, at least, as smart meters based on electronic sensing while providing advanced connectivity continue to replace these venerable glass-encased meters which have served the utility industry for over 100 years.

The latest entry into the metering IC arena is the CS548x/9x family from Cirrus Logic Inc., which supports single- and multi-phase AC line measurement of voltage and current via per-channel ADCs, and then calculates the power usage via an internal digital core. In contrast to other ICs on the market for this application, which use an SoC (system on chip) front end and a separate communications processor, the topology of the Cirrus devices puts the converters and calculating core at the front end, which the vendor claims results in lower cost through the elimination of unneeded hardware blocks (see Figure) and with fewer signal lines to isolate via optocouplers.

The CS548x/9x family of AC energy-measurement ICs from Cirrus Logic Inc. puts simultaneous A/D converters and associated power computation engine into targeted, application-specific devices (lower part) in contrast to alternative SOC-based approaches  (upper half).

[Note that the application for these IC-based energy meters goes beyond the house line and its metering. Vendors are looking to incorporate them into appliances, smart power strips, power supplies, and of course, those power-hungry servers in enterprise applications.]

Measurement accuracy for both active and reactive power (power factor) is 0.1% over a 4000:1 dynamic range, surpassing industry requirements, while current RMS measurement accuracy is 0.1% over a 1000:1 range; with readings done via simultaneous-sampling converters and 24-bit, 4^th-order delta-sigma modulators. On-chip measurements include active, reactive, and apparent power; RMS voltage and current; power factor; and line frequency, among other parameters.  

For transducer I/O—critical to this application—the ICs support shunt resistor, current transformer (CT), and Rogowski-coil pickups, with configurable digital outputs for energy pulses (an old technique but still in use), zero crossing, or energy direction. The chip's self-calibration time is under two seconds, which Cirrus claims is one-tenth the time of available devices. [Calibration time is important because these meters must be calibrated in conjunction with their sensor, at the factory production line.]

At the other side of the I/O situation, the family offers SPI and UART interfaces, depending on specific IC model. The devices operate from a single 3.3V supply, and power consumption is under 13 mW.

Packaging, pricing, and availability: Depending on specific device, the CS548x/9x family members offer 2-, 3-, and 4-channel front ends in a variety of packages including 16-lead SOIC, 24-lead QFN, and 28-lead QFN. Prices begin at $0.75 (100k lots) for the smallest member of the family. All parts are now in full production. 

For more information: go to http://www.cirrus.com.