Tesla Cybertruck has been equipped with a 48V system throughout the vehicle. The 48V mild hybrid system has expanded from luxury brands to economy models, covering over 200 models currently on sale, with a global penetration rate exceeding 50%.

The upgrade from the common 12V and 24V systems to 48V not only represents a major transformation in functional design but also requires a redefinition and redesign of the reliability that customers care about to ensure the safe operation of the main chip. The analysis and design are mainly carried out from the two aspects of power interface and signal interface (CAN interface).

A.   Why 48V system?g

Traditional fuel vehicles have used 12V low-voltage systems, but with the increasing number of automotive electronic devices (such as start-stop systems, electric air conditioners, active suspensions, electric turbochargers, etc.), the 12V system has gradually become overburdened. So the industry turned to the 48V mild hybrid system.

The main reasons are as follows:

B.    The function of 48V CAN bus

The 48V CAN bus is a standard communication network operating in a 48V mild hybrid or high-voltage architecture, responsible for connecting 12V and 48V systems to achieve coordinated control among multiple ECUs.

In modern automobiles, especially those equipped with 48V mild hybrid power systems (such as Mercedes-Benz, Audi, Cadillac, etc.), there are two main power systems inside the vehicle:

l  12V low voltage system: for traditional electronic devices (meters, lights, ECUs, etc.).

l  48V high-voltage system: Supplies power to high-power components such as start-stop motors, electric turbochargers, and air conditioning compressors.

To enable efficient collaboration between the two, it is necessary to rely on the 48V CAN bus to complete the transmission of key instructions, such as the engine ECU sending the start command to the 48V starter generator.

Three main functions of 48V CAN bus:

1) Cross-domain communication: Connect 12V and 48V systems to transmit key information such as start-stop, energy recovery, and fault diagnosis.

2) Collaborative control: Uniformly dispatch systems such as the engine, transmission, battery, and air conditioning to enhance energy efficiency and driving experience.

3) Functional support: It provides a communication foundation for functions such as idle start-stop, coasting energy saving, kinetic energy recovery, and intelligent cruise control.

C. Why does the 48V CAN bus need electrostatic protection

The standard CAN communication network operating in the 48V mild hybrid system architecture, due to its more complex working environment and higher electrical load, makes electrostatic discharge (ESD) protection particularly critical. If static electricity is not properly handled, it may lead to communication interruption, malfunction of the ECU, and even loss of control of the entire vehicle. The reasons are as follows

1、Higher voltage platforms bring greater risks of strong interference: 48V systems have a larger potential difference than traditional 12V systems. Once ESD occurs, the high voltage difference environment in 48V systems does indeed increase the coupling risk and damage potential of ESD to sensitive circuits (such as CAN buses), especially when there is a lack of effective protection.

2、Higher system integration: The 48V system connects more high-power electric drive components (such as ISG motors, electric air conditioners). These devices generate high-frequency noise and induced voltage at the moment of switching, which, when superimposed with ESD effects, increases the risk of communication distortion.

3、The consequences of communication interruption are more serious: If CAN communication is interrupted due to ESD, it may lead to start-stop failure, false triggering of airbags, black screen of the instrument panel and other problems, directly affecting driving safety.

D. Shanghai Leiditech’s protection solution for 48V architecture power interfaces and signal interfaces

1、Automotive 48V power supply PMOS reverse connection electrostatic surge protection solution

Advantages：

l  The circuit is simple；

l  The P-channel MOSFET is applied to meet the high-power anti-reverse connection requirements of automotive equipment. It features low heat generation, DFN5X6-8 packaging, and excellent heat dissipation performance；

l  SM8S58CA is used to meet ISO7637-2 5A /5B test, 5.0SMDJ58CA can pass IEC61000-4-5, GB/T17626.5 8/20μs 2KV standard, low cost。

l  It achieves with IEC61000-4-2 (Class 4) for contact discharge at 30kV and air discharge at 30kV。

2、48V CAN bus protection scheme

a）Advantages of 48V CAN bus electrostatic protection diode SD4881D3W

l  SD4881D3W 48V dedicated protection diode supports ±30kV ESD protection；

l  The closing capacitance of 20pF-30pF ensures the integrity of high-speed CAN signals；

l  It has a certain surge resistance capability, with a surge absorption current as high as 18A.

b）48V CAN bus solution：

c）The parameter list of SD4881D3W：

d）SD4881D3W could be apply in：

l   48V CAN、LIN、Ethernet and various sensor interfaces。

l   48V Power cord

l  In fields such as automotive electronics, industrial control, communication equipment and consumer electronics

l   48V is the standard distribution voltage for data centers and telecommunication equipment (-48V).

e）Shanghai Leiditech 48V multi-package electrostatic protection diodes