[Introduction]In the automotive industry, the trend of upgrading from the traditional 12V power distribution system to the 48V power distribution system is becoming more and more obvious. Especially in the context of global energy conservation and carbon reduction, with people’s in-depth understanding of the environmental protection and economic value of the 48V power supply system, the exploration on this upgrade road has become more and more active.

As we all know, the electric energy required by the on-board Electronic equipment on the car in the past is to convert part of the power of the engine into electric energy and store it in the 12V battery, and distribute it to each power unit through the 12V power bus. However, with the upgrade of vehicle architecture and functions, this 12V power distribution system is becoming more and more difficult to use.

The reason is that, on the one hand, this is because the 12V power distribution system limits the further improvement of the transmission power. With the application of the electric start-stop system of automobiles and the entry of more new automotive electronic functions such as air conditioning, ADAS and automatic driving, it is necessary to Find effective ways to break down this power “ceiling”. On the other hand, after the total system load power increases, if the voltage remains unchanged, the current needs to be increased to meet the requirements of transmitting higher power, which will not only increase the power dissipation of the electric energy during the transmission process, but also increase the required power cables. diameter and other related components, thereby increasing the weight of the vehicle and generating more energy consumption.

And if the 48V power distribution system is used, it is obviously of great benefit to improve the system power and reduce energy consumption. Research data shows that the 48V mild hybrid system can reduce the energy consumption and emissions of the entire vehicle by about 15-20%. Therefore, the 48V power system is also considered to be an important technical factor driving the transformation of traditional vehicles to new energy vehicles.

Over the technical threshold of 48V power system

Of course, as a new power supply architecture, there are still many technical “thresholds” that need to be overcome in the process of large-scale commercial use of 48V systems. For example, when a vehicle uses a 48V power system to switch between high-current loads and the battery, new safety and reliability challenges need to be faced.

In traditional 12V power systems, such switching operations are usually done by mechanical relays. An arc occurs when two relay contacts open, which extinguishes itself within milliseconds as the distance between the contacts increases. In the 48V system, due to the higher transmission power, if you want the arc to extinguish itself, you need to use a relay with a larger contact distance, or add an additional arc extinguishing control circuit, which will not only increase the overall cost of the system, but also additional of contact wear will also reduce the life expectancy of the relay. Therefore, the 48V power system needs a new solution when switching between the battery and the high current load (such as electric power steering, electric turbocharger, etc.).

To this end, Vishay has introduced a resettable electronic fuse reference design (shown in Figure 1). This solution can switch loads of up to 200A at 48V, and the whole solution is “condensed” on a small double-sided FR4 printed circuit board and requires only passive cooling. This electronic fuse can provide the necessary circuit protection functions while safely and reliably realizing the switching operation, and all operations are recoverable, which has a longer service life than traditional mechanical relays.

Figure 1: 48V Resettable Electronic Fuse Reference Design

(Image source: Vishay)

Figure 2 shows the circuit of this e-fuse reference design. It uses two sets of MOSFETs (TR2/TR3) connected in a bidirectional arrangement to handle high load currents and to prevent backflow through the MOSFET body diodes after the load is disabled. Each switch requires 10 Vishay SQJQ160E automotive N-channel MOSFETs connected in parallel to minimize path impedance to reduce power dissipation. Under 200A operating conditions, the total power consumption can be limited to less than 10W.

Figure 2: 48V Resettable Electronic Fuse Reference Design Circuit Diagram

(Image source: Vishay)

To prevent damage to the load in the event of a short circuit, the design uses four parallel 300µΩ shunt resistors (R2 in Figure 2, Vishay’s WSLP3921) to measure the load current continuously. When a current overload is detected, the controller can quickly disconnect the battery from the short-circuited load. At the same time, the body control module can also monitor the operating conditions such as the charging level and battery life of the vehicle battery through continuous current measurement through the serial interface.

During switch actuation, it is also often encountered that when the battery is first connected to the load, there may be a peak inrush current due to the presence of an uncharged capacitor bank in the load. This can cause damage to downstream components and also affect battery life, so a pre-charge circuit must be used to limit the inrush current to an acceptable level.

To address this, this reference design uses Vishay’s SQJA84E MOSFET (TR1), VSS8D5M6 Schottky diode, and D2TO20 SMD power resistor (R1) to limit the inrush current to a maximum of 5A at 48V. The design idea is that, before the load is energized, TR1 is turned on for a predetermined time of 10ms, and the output voltage X3 is monitored – if the output voltage does not reach 90% of the input voltage, assuming the load or wiring is short-circuited, the process is terminated; if the output When the appropriate level is reached, TR1 is turned off, then TR2/TR3 is turned on to turn on the load. The role of the Schottky diode is to prevent current flow back through the MOSFET body diode when it is turned off.

Additionally, in terms of protection features, the reference design uses Vishay’s NTCS0805 (NTC1) with excellent mechanical reliability under thermal stress to monitor temperature. At the same time, two TVS diodes in series – XMC7K24CA (D1a) and 5KASMC30A (D1b) – are used to protect the circuit and sensitive components from the high energy of vehicle load transients.

In a word, this is an electronic fuse reference design with comprehensive consideration, complete functions and outstanding performance, which can be used as an alternative to traditional mechanical relays to meet the design requirements of 48V vehicle power system.

Electronic Fuse Reference Design BOM Analysis

If we analyze it carefully, the secret of achieving such a “high specification” reference design, in addition to the unique design ideas and careful design considerations, is that the key components used are all carefully selected and outstanding performance “goers” “. Today we might as well go deep into the BOM of this 48V resettable electronic fuse reference design and find out.

SQJQ160E Automotive N-Channel MOSFET

It can be seen from the above analysis that the core switching function of Vishay 48V self-recovery electronic fuse is mainly realized by 10 SQJQ160Es. SQJQ160E is an automotive N-channel MOSFET developed by Vishay/Siliconix. It adopts TrenchFET®️Gen IV technology and has extremely low drain-source on-resistance (only 0.00085Ω at VGS=10V), so it can effectively reduce the conduction pass loss and overall power dissipation.

Owing to the compact PowerPAK®️8 x 8L package, the SQJQ160E has excellent thermal performance with operating junction and storage temperatures from -55°C to +175°C. This product complies with AEC-Q101 standard and meets environmental protection requirements such as halogen-free, lead-free, RoHS directive, etc. It can be said that it is an ideal choice for high power density automotive applications.

Figure 3: SQJQ160E Automotive N-Channel MOSFET

(Image source: Vishay)

D2TO20 SMD Power Resistor

Vishay/Sfernice’s D2TO20SMD power resistor is a critical component in the design of pre-charge circuits that limit load inrush current. Due to its unique physical structure and integrated heat sink, this thick film resistor provides excellent power handling and thermal conduction characteristic.

D2TO20 SMD Power Resistors are surface mount non-inductive power resistors in a TO-263 (D2PAK) package in a compact form factor with a resistance value range of 0.01Ω to 550Ω and 20W at 25°C. This product is AEC-Q200 qualified and perfect for automotive applications.

Figure 4: D2TO20 SMD Power Resistor

(Image source: Vishay)

XMC7K24CA XClampR™ TVS Diode

Vishay 48V Resettable Electronic Fuse Solutions Vishay General semiconductor‘s XMC7K24CA XClampR™ TVS diode plays an important role in transient voltage suppression.

Specifically, the XMC7K24CA features ultra-low clamping voltage, low leakage current and 7000W peak pulse power (PPPM), its maximum operating voltage (VWM) is 24V, its peak pulse current (IPPM) is 180A, and its storage temperature range (TSTG) is -55°C to 175°C. It is particularly worth mentioning that the TVS diode has high temperature stability and high reliability, and meets the AEC-Q101 standard. It is obviously a wise choice to include it in the BOM of automotive 48V power supply related solutions.

Figure 5: XMC7K24CA XClampR™ TVS Diode

(Image source: Vishay)

Summary of this article

The development of automobile 48V power supply system is the general trend, but like all technological upgrades, this process is not smooth, and new technologies and solutions are needed to fill the gaps.

For example, when switching between a battery and a high-current load, it is necessary to use a resettable electronic fuse to replace the traditional mechanical relay solution to meet safer and more reliable design requirements.

The resettable electronic fuse reference design created by Vishay in accordance with this design requirement has both ingenuity in design and careful selection of materials. It has penetrated the design secrets, and the application development of automotive 48V power supply system will also become a smooth road. Allows you to speed up and run on it.

Source: Mouser Electronics