The transition to Software Defined Vehicles (SDVs) has prompted car manufacturers to continuously innovate by integrating protected semiconductor switches into regional controllers. Electronic fuses and SmartFET can provide protection for loads, sensors, and actuators, thereby improving functional safety and better responding to functional failure situations. Unlike traditional domain architectures, the regional control architecture adopts a centralized control and computation approach, where software scattered across various ECUs is uniformly processed by a powerful central computer, providing higher flexibility for downstream electronic control and power distribution.

system description

Low voltage distribution in electric vehicles

Low voltage (LV) power grids play a critical role in all vehicle models. The regional control architecture is also deployed in hybrid power systems, and here we will only focus on introducing the regional control architecture of electric vehicles. As shown in the diagram below, the power comes from a high voltage (HV) battery pack (typically a 400 V or 800 V battery architecture). The HV-LV DC-DC converter steps down high voltage to supply power to the LV network, typically using a 48V or 12V battery architecture. Some cars only have one type of LV battery, while others have two types of batteries, each using a separate converter, depending on the manufacturer and car model.

Main components of low-voltage distribution system

The 48V and 12V power grids may coexist in the same vehicle, so the HV-LV converter can directly supply power to the 48V battery, while the additional 48V-12V converter can act as an intermediate step-down stage. In the centralized L V distribution mode, a single larger 48V-12V converter (approximately 3kW) charges a 12V battery.

In contrast, the regional control architecture adopts a distributed approach, embedding multiple smaller DC-DC converters in the regional controller (ZCU).

When using separate power distribution units (PDUs) and ZCUs, power flows from the power source through the PDUs and ZCUs to reach various loads within a specific area. PDU is located before ZCU and can also directly supply power to high current loads. ZCU is responsible for distributing power to most of the loads within the designated area of the vehicle. The following diagram visually presents the power flow and different implementation schemes.

There are currently two main methods on the market:

·Integrated PDU and ZCU: Integrating PDU and ZCU functions into a single module.

·Separate PDU and ZCU: Use independent PDU and ZCU units.

Switching from blade type fuses to protected semiconductor switches

For a long time, car fuses have been the standard solution for protecting circuits and downstream loads from overcurrent effects to prevent fires caused by overcurrent. The working principle of traditional blade type fuses is simple and critical: it contains a calibrated filament. If the current is too high within a specific time (I2t), the filament will melt, causing the circuit to open and interrupt the current. The selected filament material and its cross-sectional area determine the rated current of the fuse.

With the adoption of regional control architecture, vehicle manufacturers and first tier suppliers are increasingly replacing blade fuses with protected semiconductor switches, greatly improving functional safety. Unlike traditional fuses (which must be replaced after melting), protected semiconductor switches can reset and do not need to be replaced in the event of a trip, making them more advanced. Onsemi offers three types of such switches: electronic fuses, SmartFETs, and ideal diode controllers.

This type of new device has the following application advantages:

·Strengthen load protection and safety: In the event of a short circuit, intelligent retry mechanism and fast transient response will be activated to help limit current overshoot. The flexibility is greatly improved, which helps to enhance functional safety and better cope with functional failure situations.

·Easy to integrate: This type of switch can be easily integrated into larger systems through a microcontroller (MCU), providing configuration, diagnostic, and status reporting functions.

·Resettable: Unlike traditional fuses, this type of switch does not require replacement after tripping, allowing for flexible protection schemes and threshold adjustments.

·Compact size: After the device size is reduced, it is more conducive to integration into the regional control architecture, saving space and simplifying the vehicle wiring harness.

Overview of the Plan

Power Distribution Unit (PDU) - Block Diagram

Power Distribution Unit (PDU) is a key component in the vehicle area control architecture, responsible for initial power distribution in the distribution hierarchy. The PDU is connected to the output of the vehicle's low-voltage (LV) battery (usually 12V or 48V) or HV-LV DC-DC converter, which reduces the voltage of the high-voltage (HV) battery.

PDU can intelligently distribute power to various areas inside the vehicle, ensuring efficient and reliable power management. PDU can directly supply power to high current loads or distribute power to multiple zone controllers (ZCUs). ZCU further manages power distribution within their respective regions, greatly reducing the weight and complexity of the wiring harness. There are currently multiple options available to meet the specific requirements of different car manufacturers and their models. The following diagram briefly illustrates the composition structure of PDU:

SmartFET for upper and lower bridge protection

Lower Bridge SmartFET - NCV841x "F" Series

Ansenmei offers two series of lower bridge SmartFETs: the base NCV840x and the enhanced NCV841x. The pins of these two series are compatible with each other and use the same packaging. NCV841x has improved RSC and short-circuit protection performance, significantly extending the device's lifespan. The NCV841x SmartFET adopts temperature difference thermal shutdown technology, which can effectively prevent high thermal transients from damaging the device and ensure excellent RSC performance.

The NCV841x series has a very flat temperature coefficient and can maintain consistent current limitation within the temperature range of -40 ℃ to 125 ℃. Due to being largely unaffected by temperature, there is no need to choose thicker wires to cope with increased current in cold weather conditions. Reducing wire size helps to lower the cost and space occupation of vehicle wiring harnesses.

The main features of NCV8411 (NCV841x series) are:

·Three terminal protected intelligent discrete FET

·Temperature difference thermal shutdown and over temperature protection, supporting automatic restart

·Overcurrent and overvoltage protection, integrated drain to gate clamping and ESD protection

·Fault monitoring and indication through gate pins

Ideal diode and bridge switch NMOS controller

NCV68261 is a polarity reversal protection and ideal diode NMOS controller with optional upper bridge switch function, which has lower losses and forward voltage than power rectifier diodes and mechanical power switches, and can replace the latter two. This controller works in conjunction with one or two N-channel MOSFETs and sets the transistor's on/off state based on the status of the enable pin and the polarity of the differential voltage input to the drain. Its function is to regulate and protect the car battery (power supply), with a maximum operating voltage VIN of 32 V and the ability to withstand up to 60 V load drop pulses. NCV68261 adopts a very small WDFNW-6 package, which can achieve protection function in a very small space.

This controller can be easily controlled through the drain pin and supports ideal diode working mode (Figure 2) and polarity reversal protection working mode (Figure 3).  

Evaluation Board (EVB)

The following two ideal diode controllers can both use the evaluation board: NCV68061 and NCV68261. Users can use the evaluation board to test the controller in various configurations and set the required protection mode through the jumper on the evaluation board. The connected power supply voltage should be between -18 V and 45 V, and should not exceed the maximum rated value of the device. By attaching jumper wires, the preset layout of the evaluation board can be used or external connection signals can be used to control the device.

T10 MOSFET technology: 40V-80V low and medium voltage MOSFETs

T10 is the latest technological milestone launched by Anson after the success of T6/T8. The new shielded gate trench technology improves energy efficiency, reduces output capacitance, RDS (ON), and gate charge QG, and improves quality factor. T10-M adopts a specific application architecture with extremely low RDS (ON) and soft recovery diodes, optimized specifically for motor control and load switching. On the other hand, the T10-S is designed specifically for switch applications, with a greater emphasis on reducing output capacitance. Although sacrificing a small amount of RDS (ON), the overall energy efficiency is better, especially at higher frequencies.

·RDS (ON) and gate charge QG decrease overall, while Rsp (RDS (ON) relative to area) is lower

·In 40V devices, NVMFWS0D4N04XM has a very low RDS (ON) of only 0.42m Ω.

·In 80V devices, NVBLS0D8N08X has a very low RDS (ON) of only 0.8m Ω.

·The improved FOM (RDS x QOSS/QG/QGD) has improved performance and overall energy efficiency.

·Industry leading soft recovery diodes (Qrr, Trr) reduce ringing, overshoot, and noise.

Ansenmei provides a variety of LV and MV MOSFETs for 12V, 48V PDU and ZCU. You can further understand the solutions provided by Ansenmei through the product series listed in Table 1.

There are multiple device technologies and packaging options for designers to choose from. The alternative design solution is a compact 5.1 x 7.5 mm TCPAK57 top heat dissipation package, which can dissipate heat through the exposed drain on the top of the package.

The current level in the PDU is significantly higher than the current level inside a single ZCU, so a discrete MOSFET scheme with RDS (ON) below 1.2 m Ω can be considered. Another solution is to parallel multiple MOSFETs inside the PDU, which can further enhance the current carrying capacity. In ZCUs with low current consumption, designers can choose SmartFETs with advanced protection features such as the new SmartGuard function. image.png

Wafer thinning

For low-voltage FET, substrate resistance may account for a significant portion of RDS (ON). Therefore, with the advancement of technology, it has become crucial to use substrates with lower resistivity and thin wafers. In T10 technology, ON Semiconductor successfully reduced the wafer thickness, thereby reducing the substrate's contribution to RDS (ON) in 40V MOSFETs from approximately 50% to 22%. Thinner substrates also improve the thermal performance of the device.