Introduction:
As 48V battery electric vehicles (BEV) are being introduced to the market, many global carmakers are considering the transition from 12V to 48V within their automotive systems. As 48V was previously only used to improve efficiency in mild hybrid vehicles, there are challenges to implementing a 48V low-voltage architecture in BEV, hybrid electric vehicles (HEV) and plug-in hybrid electric vehicles (PHEV) generating 48V off a high voltage battery. This presentation will outline 48V architectures and potential design solutions for 48V in future electric vehicles (EVs). Electric or hybrid vehicles generating 48V off a high-voltage battery can realize an important benefit of 48V systems: adding a 48V low-voltage rail reduces the gauge of the wire harness that supplies power throughout the vehicle and reduces the load current requirements of downstream semiconductor components such as power switches and motor drivers. Thus, transitioning to 48V systems impacts power distribution, load actuation, and power conversion.

Power Distribution:
• Vehicle Power Distribution:
With the introduction of smart eFuses, original equipment manufacturers (OEMs) are enhancing their systems by replacing accessible fuse boxes managed by the driver with electronic fuse boxes managed by vehicle software. Power distribution networks feed vehicle power supplies into a power distribution board (PDB), which distributes power to each zone. Each zone then distributes power locally to nearby electronic control unit (ECUs), actuators or sensors.
• 48V vehicle architecture:
When optimizing wiring harnesses for 48V architectures, OEMs will need to evaluate different architectures. Figure 2 shows three options when implementing a 48V low-voltage rail: 48V primary distribution and 12V local, 48V distribution and 12V distribution, or 12V distribution and 48V high current loads only.
• 48V backbone power distribution with smart eFuses
48V systems enable further evolution by allowing you to use a backbone architecture where zone control modules distribute both primary and secondary power. It then becomes possible to remove the Power Distribution Box (PDB).

When designing a backbone power distribution using smart eFuses, take the following into consideration: always on power rail, the path for exiting low-power mode, and the direction of short circuit or I2T protection. During parked state (low power mode), generally 48V battery voltage would be higher than the HV/48 DCDC output (HV/48 DCDC is disabled). Thus, low power mode needs to wake from right to left as shown in Figure 3.

Load Actuation:
Adopting a 48V low voltage rail has a clear benefit, but where is the line and which loads make the most sense to transition? In a vehicle, majority of the power is consumed by about 10% of the loads. Thus, high power loads such as, electronic power steering and window lift should all move to 48V. By only moving high power loads to 48V, a large system benefit can be realized. Figure 4 shows examples of motor loads broken into three categories: low power, mid power, and high power.

Power Conversion:
The transition to 48V power distribution will take time, as not all loads and actuators are ready to make the jump to this higher voltage level. As a result, DCDC converters will supply remaining 12V loads in first generation 48V systems. The specific 48V to 12V, 5V, or 3.3V conversion needs will vary based on each system. Due to different power requirements, various topologies are being considered: buck, buck-boost, switched capacitor converter (SCC), and inductor-inductor-capacitor (LLC), e.g. a Switched capacitor converter.
Due to many legacy 12V loads, the zone control module may need to supply 500W at 12V. The switched
capacitor converter has gained significant popularity at customers due to bi-directional power flow, open loop unregulated output, and high efficiency.

Summary:
This presentation introduces how vehicle power distribution is changing in next generation vehicles and explores possible solutions for the 48V backbone power distribution, load actuation, and 48V to 12V, 5V, or 3.3V conversion.