Maxim Chipset Eliminates Costly Current Transformers In Polyphase Energy Meters
Maxim Integrated Products introduced a new chipset, the MAXQ3108 and DS8102, that is said to reduce the bill of materials (BOM) cost of a polyphase energy meter. Together, Maxim claims that 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 digital signal processor that computes the power, energy, power factors, and RMS voltage and current parameters required for a multifunction electricity meter.
The MAXQ3108 and DS8102 chipset is thus said to reduce total system cost and deliver 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 data-acquisition instrument is required. Reference designs are available for assistance.
The DS8102 modulator and encoder and the MAXQ3108 microcontroller are said to 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. According to the company, the expensive current transformer is thus eliminated and BOM costs reduced significantly.
The MAXQ3108 is packaged in a 28-pin TSSOP and the DS8102 in a 16-pin TSSOP. Both devices operate over the -40 to +85°C temperature range. Prices are $2.43 for the MAXQ3108 and $1.17 for the DS8102 (1000-up, FOB USA).