32-bit MCUs for smart meters feature large memory and a 24-bit delta-sigma ADC

September 06, 2012 // By Julien Happich
The RX21A Group of 32-bit microcontrollers (MCUs) announced by Renesas Electronics is aimed at smart meters with advanced functionality. The new MCUs are claimed to be the first in the industry to combine large flash memory capacity of 512 KB and a 24-bit delta-sigma (Delta-sigma) A/D converter for high-resolution measurement.

The RX21A Group of MCUs implements in a single chip functions that previously required separate devices, such as power measurement, meter control, calculation of electricity charges, and data encryption. This reduces the number of external components required and helps to lower the overall cost. In addition, the RX21A Group includes product versions for a variety of meter models, allowing common and effective system design. The RX21A Group of MCUs integrates a newly-developed 24-bit Delta-sigma A/D converter module that delivers higher resolution than the 16-bit module of existing MCU products. The new MCUs incorporate in a single chip all the main functions required by smart meters, including encryption engine, real-time clock (RTC) with tamper, temperature sensor, and IrDA.3 (Infrared Data Association). This reduces the total number of components required and lowers the overall system cost.

The 24-bit Delta-sigma A/D converter achieves conversion accuracy (SNDR) of 85 dB, and the encryption engine supports AES (256-bit key length). This provides smart meters with improved calculation precision and enhanced security functionality, such as communication data protection and unauthorized data access prevention that will be needed for the next- generation smart meters. The RX21A MCUs also feature a large on-chip flash memory with a capacity of up to 512 KB, twice that of Renesas' existing products, to accommodate larger programs. Based on the advanced 32-bit RX CPU core, the RX21A Group of MCUs only draws 0.2 mA/MHz. Power consumption in standby mode is only 1.0 microampere (μA) when the RTC is operating and 0.3 μA when the RTC is stopped. These enhancements enable system designers to develop smart meters with reduced power consumption and smaller backup batteries.

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