Appliance Design - October 2008 - (Page 30)

ELECTRONICS SAFE CONTROL M ST 32 m oc icr on l tro ler is as Cl sB re ad y. Self-diagnosing MCU is Class B ready. S by vincent onde Vincent Onde is application engineer at STMicroelectronics MCU Division in Rousset, France. 30 applianceDESIGN October 2008 ince October 2007, all new household appliances have to comply with the IEC60335 norm, which is intended to prevent any dangerous malfunction in case of a fault condition. The 4th edition of the standard has garnered attention from designers of electronic controls for home appliances, and more specifically software developers for such controls, with the introduction of software inspection and the notion of software classes. Depending on the class (A/B/C), a list of MCU components (such as CPU registers or memories) have to be tested at power on and monitored during run-time, similar to what is done in industrial or medical segments for safety critical applications, those evaluated according to SIL2/SIL3 levels, IEC61508, or UL1998 standards. For designers of home appliances, it is important to understand how to fulfill Class B requirements and how a microcontroller manufacturer can help minimize development cost overhead and get their application certified. For example, the STMicroelectronics CortexM3-based STM32 32-bit MCU is considered a Class B ready device that can reduce the time and expense associated with complying with the new standard. The standard distinguishes three software classes, depending on how dangerous a piece of equipment is in case of failure. If the safety of the appliance does not rely on software, it falls into Class A. This class would include such things as room thermostats or lighting controls. On the opposite end of the class spectrum, if the software is intended to prevent special hazards, such as an explosion in electronically-fired gas burners, it will be evaluated as Class C. However, the vast majority of household appliances whose electronic controls must prevent unsafe operation belong to the Class B category. Examples include clothes washers with electronically controlled door locks or dishwasher pump drives with motor over-temperature detection. For the Class B checklist, the IEC60335 standard refers to another norm, the IEC60730, which covers electronic controls in general. The table H.11.12.7 in Annex H lists the microcontroller components to be tested, the faults to be detected, and the acceptable measures, for both software Class B and C. It includes the CPU www.applianceDESIGN.com http://www.applianceDESIGN.com

Table of Contents Feed for the Digital Edition of Appliance Design - October 2008

Appliance Design - October 2008 Contents Editorial Shipments/Forecasts News Watch Prototyping - Materials Play the Part Prototyping - Mix & Match Motors Electronics Coatings Design Marts Association Report: AHRI Advertiser's Index

Appliance Design - October 2008

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