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Chipset replaces transformers in energy meters

Posted: 19 Mar 2009 ?? ?Print Version ?Bookmark and Share

Keywords:chipset transformer? energy meter? microcontroller? DSP?

Maxim Integrated Products has released the MAXQ3108 and DS8102 chipset that reduces the BOM cost of a polyphase energy meter. Together, the MAXQ3108 and DS8102 replace three high-cost current transformers with three low-cost shunts to save both cost and space.

The DS8102 contains two high-precision second-order delta-sigma modulators with programmable gains up to 32x. The modulators' outputs are encoded into a single bit stream to minimize the isolation and data-coupling cost. The data processing is carried out in the MAXQ3108, a dual-core microcontroller that accepts three DS8102 output bit streams, then decodes and decimates that data to produce raw ADC samples across a wide dynamic range. The ADC samples are fed into the MAXQ3108's integrated DSP that computes the power, energy, power factors, RMS voltage and current parameters required for a multifunction electricity meter.

The MAXQ3108 and DS8102 chipset thus reduces total system cost and delivers high performance and flexibility for polyphase electricity meters. The MAXQ3108's DSP is also programmable, making the chipset suitable for a wide variety of industrial data-acquisition applications where isolation between the physical signals and the DAQ instrument is required. Reference designs are available for assistance.

The dual-core MAXQ3108 contains two 16bit RISC processors. The user core packs 64Kbyte flash program memory, 2Kbyte data SRAM and 16byte battery-backed (VBAT) data SRAM. It features digitally trimmable real-time clock as well as SPI, I?C, dual USART ports. The MAXQ3108 also includes hardware multiplier, three Manchester decoders and three cubic-sinc filters and 10MHz FLL with 32kHz input.

Meanwhile, the DSP core contains 8Kbyte user-loadable SRAM code memory, 1Kbyte data SRAM and hardware multiplier. If the DSP processor is disabled, the DSP code memory can be configured as data memory for access by the user core. In this configuration the user core has access to 10Kbyte of data memory. The ADC samples (from the decimators) can be made available to either the DSP core or the user core.

The DS8102 integrated two second-order delta-sigma modulators with programmable gain up to 32x. It also packs Manchester encoder, internal 8MHz oscillator and internal reference.

Added flexibility
The DS8102 modulator and encoder and the MAXQ3108 microcontroller form a unique solution to the isolation and data-coupling challenge for today's polyphase energy meters. A three-phase meter uses three DS8102s and one MAXQ3108. Each DS8102 floats on the respective phase that it is measuring. A DS8102 converts the voltage and current inputs into a high-frequency digital bit stream that is then coupled to the MAXQ3108 through a low-cost capacitor. The MAXQ3108 is DC isolated from the three DS8102s, but AC coupled to them to accept the digital data bit streams from each. With each DS8102 isolated from the other phases and from the MAXQ3108, each phase can use a shunt resistor for its current sensing. The expensive current transformer is thus eliminated and BOM costs reduced significantly.

There is yet another advantage to this solution: the data coupling is now digital, suffering no loss of fidelity across any analog input range.

The MAXQ3108 is packaged in a 28-pin TSSOP and the DS8102 in a 16-pin TSSOP. Both devices operate over the -40C to +85C temperature range. Prices are $2.43 for the MAXQ3108 and $1.17 for the DS8102 (1,000-up, FOB USA).

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