The drive for lower emissions standards combined with the increasing electronics content in automotive especially in higher power applications such as active suspension, regenerative braking and various electrical motors and pumps are driving the need to consider supplementing the 12V rail with a higher voltage. The automotive Industry has been considering this higher voltage node for decades, starting with the 42V proposal in the 90’s finally settling the level at 48V systems. The 48V rail provides enough guard band to avoid the 60V shock threshold avoiding the need for extra protection, the orange cabling/connections and specialized support equipment in the case maintenance and accidents.
The main goal of the dual 12/48V architecture is to optimize the existing mild and micro-hybrid technologies today such as stop start and regenerative braking. The 48V systems enables the electrification of high power consuming applications that are currently driven by a mechanical belt in the likes of heating and cooling components and roll stabilization systems. The future goal is to improve carefully selected existing systems that were already electrified for example electric power steering (EPS). These improvements could cover simplification of the electric systems as well as simplified assembly technologies and reduced overall system cost. On average, estimates show the 48V mild hybrid systems will provide a CO2 emissions reduction of 10-20%. While cost is added to the system, 48V systems are estimated to be ~50% cheaper than full hybrid and electric vehicles and provide a good compromise to meet the stringent <95g/km fleet average CO2 emissions by 2020. Automakers are considering several flavours of 48V system configurations designated by a Px terminology currently ranging from P0 to P4 with P0 as shown below with BSG and the rest of Px adding e-motors on drivelines/axles.
A simplified 48V Architecture – P0 System
In preparation for the 12/48 dual power supply architecture system in automotive, ON Semiconductor is working on a number of 48V system solutions targeting the 12/48 DC/DC converters as well as solutions for the increasing number of 48V loads. Our 80/100V MOSFETs are available in various discrete packages such as standard TO (transistor outline) packages as well as small 5x6mm flat lead packages for compact and efficient designs (NVMFS family & power trench technology MOSFETs). ON Semiconductor also offers MOSFET Modules such as APM19 (80V 135A FTCO3V85A1) for 48V DC/DC and APM17 (80V 540A FAM08A50DT1) for BSG starter-generator application. Bare die solutions are also available for customers building specific Modules. In addition, we have drivers (NCV5183 & FANxx family) and our NCV40x family of 80V CMR (common mode range) current sense amplifiers suitable for the 48V net. ON Semiconductor is also working on the next generation solutions targeting protection for 48V systems with the eFuse technology as well as weight/space savings with wideband gap solutions for reduction of the DC/DC using GaN.
LV148/VDA320 Specification for 48V
Challenges in the development of 48V systems exist in various forms such as standardizations, system definition expansion and specific areas of concern such as arcing/fusing. Current specification for 48V exist with LV148/VDA320, however, a wider worldwide standard encompassing inputs and requirements from various regions and OEMs will enable accelerated developments and acceptance for systems and components in automotive 48V systems. The ISO has initiated ISO21780 standardization group tasked with developing such a specification. Another issue with fusing/arcing comes as the number of 48-volt high-power loads rise and along with the necessity to use electric power distributors to monitor current paths electronically (in addition to the deployment of safety fuses) so that even creeping short circuits can be detected and switched off in the event of a fault. In addition, it must be ensured that the separation of both the 48-volt and 12-volt systems is maintained at all times. A 12/48-volt short circuit would cause considerable damage to all 12-volt control units and loads. As a result, arcing and loss of ground are among the top issues currently posing challenges in the 12/48V dual power supply system for automotive. While the challenges remain to be solved, recent reports are estimating between 3 to 5million 48V system vehicles in the market by 2020.