New-Tech Europe Magazine | Jan 2018

Fast and Straightforward Implementation of Serial Interfaces

Hans-Peter Lüdeke, Murata Europe

Serial interfaces are in widespread use in electronic devices for communication with external devices. For the majority of these interfaces, standard solutions are available today based on ICs and discrete components. In specific cases, however, it may make sense to replace a discrete approach with an all-in-one interface module providing a turnkey solution with minimum development overhead. Serial Interface Electric devices need interfaces to communicate with their environment or with other devices. Serial interfaces are prevalent for this purpose because they are often easier to handle. Depending on the application sector and the transmission capabilities required, multiple standards have entered the market over the last decades. These standards are generally based on different hardware and especially on different software protocols. Thus, it is

no surprise that device designers often need to implement a variety of software protocols to enable communication with multiple devices using today’s standards and maybe to ensure compatibility with legacy devices. Electrical Isolation Problems that may result from the spatial configuration of communicating devices and the existing electrical installation often lead to the use of a galvanically isolated interface implementation. Possible issues include potential differences between the grounding points of a large electrical installation. Devices often get their power supply from different domains of the electrical installation. This may result in communication faults in serial interfaces including RS-485. Possible ground loops impacting the signals to be processed are a general problem that galvanic isolation can mitigate significantly.

Legal regulations can be another reason for choosing an isolated interface implementation. For instance, the legislator mandates that all interfaces of medical devices meet the requirements of electrical safety, especially in case of possible patient contact. Isolated Power Supply If an isolated interface implementation is required, the corresponding data transfers must use a signal isolator, while the power supply must be galvanically isolated using a DC/DC converter. Discrete Implementation or Turnkey Module? Many manufacturers of signal isolators, which are often implemented as integrated circuits (ICs), also provide examples of the implementation of the necessary DC/DC converter. It is common to build a straightforward, discrete SMPS consisting of switches,

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