Galvanic isolation key to 48V electrical architectures

Galvanic isolation key to 48V electrical architectures

New Products |
By Christoph Hammerschmidt

“The new 48V electrical architecture pushes the envelope in terms of electromagnetic compatibility and safety requirements,” said Carlos Pardo, CEO and co-founder of KDPOF. “New safety precautions are needed, since even a single malfunction between the 48-volt and the 12-volt electrical system will lead to a short circuit, which can damage the entire 12-volt system due to overvoltage.”

Optical connections with POF provide galvanic isolation for 100 Mbps and 1 Gbps Ethernet compatible solutions with enough margin to withstand the harsh automotive environment. Applications such as Battery Management Systems (BMS) and Integrated Smart Antenna (ISA) modules profit from the inherent Electromagnetic Compatibility (EMC) of POF.

The chassis is a common ground potential for all 48-volt ECUs in the car. As the chassis has a non-zero impedance, a significant return current will be conducted through it, and a portion of this return current will find its way through a parallel path: the copper cables‘ shielding. “An OEM has stated that the shield of Shielded Twisted Pair (STP) cables can conduct more than 8A of return current due to the 48-volt jump start effect,” said Pardo. 

The need for a ubiquitous communications network within the vehicle, and particularly between ECUs belonging to different voltage domains, represents a source of potential hazards. This imposes the additional requirement of galvanic isolation between the communicating nodes. Any event that could cause the 48V to cross into the 12V, for example due to line transceivers that don’t provide sufficient galvanic isolation, might destroy the ECUs in the 12V domain. 

Hybrid architectures based on a two-voltage power line of 12 and 48V are already in the advanced marketing announcements of OEMs and Tier-1. As a further example of this new industry-wide technological trend towards 48V power supply and the handling of it, the German VDA published recommendation 320, which covers electric and electronic components in vehicles for the development of a 48V power supply. It defines requirements, test conditions and tests performed on electric, electronic and mechatronic components and systems for use in motor vehicles with a 48V on-board power supply. 

Galvanic isolation is also necessary between the primary and secondary systems of both AC-DC and DC-DC converters due to the presence of hazardous high voltage (above 25 Vac or 60 Vdc). According to the FMVSS 305 and ECE-R standards, the isolation barrier between the battery and exposed conductive parts should maintain 500 Ω/V before and after a crash impact. “This is a tough requirement that is very hard to reach without a nearly perfect isolation that copper-based networks are unable to ensure,” said Pardo. The BMS is also a very noisy environment and communications are susceptible to disturbance by conducted and radiated RF emissions. Optical communications have been demonstrated to be the most robust regarding EMC.

Related stories:

If you enjoyed this article, you will like the following ones: don't miss them by subscribing to :    eeNews on Google News


Linked Articles