an5321：Safety Class B with PMSM Sensorless Drive

1. Introduction Safety is an obligatory part of many applications. It is controlled by international standards related to electrical devices. The affected devices are those that, in case of failure, can cause injury, death, pollution, or other dangerous situations. It is a difficult task to fulfill the safety requirements. This application note describes the software part of the application safety. It provides a complex overview of the appliance safety software and you can use it as a guide for creating such software. 1.1. Audience If you plan to develop software for the Class B-related applications, this application note is a good starting point. If you are new to the field of safety applications, going through this application note can save you a lot of time and effort. The applications that are a part of the Safety Class B are indirectly specified by the IEC/UL 60335. The most common applications are: washing machines, dishwashers, dryers, induction cooking, circulating pumps, compressors, refrigerators, and other. This application note is also targeted for all engineers and designers who work on similar applications. . Scope of this application note This application note focuses mainly on safety application software, which is only a part of the complex requirements for safety applications. To fulfill software requirements, tests of the respective components stated in the international standards (IEC/ UL 60730 and IEC/UL 60335) must be implemented. To get detailed information about most of the standards, look for the NXP Safety Class B library. The information provided in this document is essential to implement the components. This application note is provided together with the example application, where the safety library and safety software are integrated into a real motor control application. The parts of code from the example application are discussed in this document for a better explanation. The majority of the required Class B tests is implemented and described. This is the list of the implemented tests: • CPU registers—tested for the “stuck at” condition. • Program counter—tested for the “stuck at” condition. • Flash memory—tested for the single bit error and multiple bits error. • RAM—tested for the “stuck at” condition and direct coupling faults. • Clock source—tested for the “wrong frequency” condition. • Watchdog—tested for wrong frequency and proper functionality. • Application stack—the same test as for the RAM and the overflow and underflow conditions. • Interrupt handling and execution—the interrupts are tested for too frequent or too infrequent