Power Electronics
Energy Metering ICs Make Better Use of Batteries

Energy Metering ICs Make Better Use of Batteries

Two families of system-on-a-chip energy meter ICs from Analog Devices (www.analog.com) address a number of battery management challenges faced by designers of feature-rich electronic energy meters. Targeting single-phase applications with LCD displays, the ADE7100 and ADE7500 include battery modes that maintain operation of a real-time clock (RTC), sense temperature changes, and run the LCD readout when ac power is lost. At the same time, these chips consume at least 40% less power than competitive solutions, according to the vendor. Furthermore, Analog Devices claims that these devices perform functions previously requiring as many as six discrete ICs.

The ADE7100 and ADE7500 use an energy measurement core derived from the ADE7755. The company notes this is the same core that has been designed into more than 175 million energy meters worldwide. In addition to the energy measurement core, these devices include an ‘8052 microprocessor, flash memory, LCD driver, RTC, and intelligent battery management circuitry (see the figure). According to the vendor, designs based on these chips provide a solution that is less susceptible to system failures and enables advanced services like remote meter-reading, time-of-use billing, and load shedding.

The chips’ battery management capabilities offer several benefits. The ability to measure temperature even when powered by the battery makes it possible to compensate for frequency shifts in the external crystal and maintain the accuracy of the RTC. The chips can also provide alerts for wake-up events in battery mode. Current consumption in battery or sleep mode is just 1.2 µA. In addition, these chips extend battery life by operating from supply voltages as low as 2.2 V.

Another advantage is how the chips manage the switchover to battery power when a power outage occurs. The switchover function is fully integrated within the ‘7100 and ‘7500, so no additional components are needed. Moreover, the switchover is based on absolute voltage values rather than relative values.

The ADE7100 and ADE7500 families integrate an LCD driver that meets industrial temperature specifications for all outdoor climate conditions. On-chip charge-pumps controlled by a D-A converter allow designers to adjust LCD contrast by setting the drive voltage up to 5.4 V with a power supply of 3.3 V. This capability ensures the display is clearly visible even as temperature ranges fluctuate from -40ºC to 85ºC. Furthermore, the use of the charge pump produces lower dc offset in the LCD drive signals than the conventional resistor ladder design. Lowering that offset enables longer operating life for the display.

Analog Devices’ energy metering core includes active, reactive and apparent energy calculations, as well as voltage and current rms (root-mean-square) measurements. Power supervisory features include SAG detection, peak and zero crossing. The ADE7100 family of products feature a second current input for tamper detection.

Four products in the ADE7100 (ADE7166, ADE7169) and ADE7500 (ADE7566, ADE7569) families are sampling now with full production scheduled for February 2007. The devices are available in 64-lead LQFPs and are priced under $3.00 per unit in 1,000-piece quantities. For more information, visit www.analog.com/pr/ADE7169.

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