New IC simplifies the design of 48 V/12 V dual-battery automotive systems

Introduction

The application of 48 V/12 V battery systems in the automotive field is just around the corner. In the past few years, most major automakers in the world have struggled to prove the applicability of their systems. At present, it is clear that these systems are expected to be implemented in the short term. This is a necessary and critical step in the long and arduous process of realizing unmanned and truly autonomous passenger vehicles. Nonetheless, this does not mean that 12 V batteries will be withdrawn from the market; this is unlikely to happen because there are too many old systems in installed vehicles. In other words, autonomous vehicles will use 12 V batteries and 48 V batteries at the same time.

 New IC simplifies the design of 48 V/12 V dual-battery automotive systems 

Figure 1. The new generation of cars will be powered by 12 V and 48 V batteries

This means that the internal system of the vehicle will use either a 48 V lithium ion (Li-Ion) battery or a 12 V enclosed lead-acid (SLA) battery, but both cannot be used at the same time. However, due to the chemical nature of these two batteries, in addition to designing two independent charging circuits for them, a mechanism must be used to allow charge to flow between them without causing any damage to the battery or any system in the car. Any damage. In addition, considering that one of the batteries fails during operation, the use of two batteries can provide redundant power.

Although this will certainly complicate the design of various electrical subsystems in the vehicle, there are also some advantages. According to some automakers, electrical systems based on 48 V can increase the fuel economy of internal combustion engine vehicles by 10% to 15%, thereby reducing carbon dioxide emissions. In addition, the future use of 48 V/12 V dual-system vehicles will allow engineers to integrate electric booster technology that operates independently of engine load, thereby improving acceleration performance. This type of electric supercharger is already in the advanced stage of development, and will be located between the bleed air system and the intercooler, using a 48 V voltage rail to rotate the turbine blades.

Globally, fuel economy regulations are becoming stricter, and networked autonomous driving functions are becoming more and more popular in new vehicles. Therefore, the 12 V automotive electrical system has reached the limit of its available power. At the same time, these changes do not seem to be enough, and the demand for automotive Electronic systems has also grown significantly. Coupled with related power requirements, these changes have created a whole new set of engineering opportunities. Obviously, the 12 V lead-acid battery automotive system with a power limit of 3 kW must be supplemented.

In addition, there are new automotive standards that affect how these systems work. The newly proposed automotive standard (called LV 148) combines the secondary 48 V bus with the existing automotive 12 V system. The 48 V power rail includes an integrated starter generator (ISG) or belt starter generator, 48 V lithium-ion battery, and a two-way DC-DC converter that can provide 10 kW of energy from 48 V and 12 V batteries. This technology is suitable for traditional internal combustion engine vehicles, hybrid vehicles and mild hybrid vehicles, and can help automakers meet increasingly stringent carbon dioxide emissions targets.

A new power solution for 48 V/12 V battery systems

This new standard requires the 12 V bus to continue to power ignition, lighting, infotainment, and audio systems. The 48 V bus will power the active chassis system, air conditioning compressor, adjustable suspension, electric supercharger/turbocharger, and even support braking energy recovery.

Adding a 48V power supply network to the vehicle is not without significant impact. The electronic control unit (ECU) will be affected and its operating range will need to be adjusted to a higher voltage. This requires DC-DC converter manufacturers to use dedicated ICs to achieve this high-power transmission.

Therefore, ADI’s Power by Linear? (PbL) product department has designed and developed some DC-DC converters that can achieve this energy conversion with very high efficiency, thereby minimizing heat dissipation design problems while saving energy. .

Obviously, this requires the use of a bidirectional buck and boost DC-DC converter between 12 V and 48 V batteries. This kind of converter can be used to charge any one of the batteries, and can allow two batteries to supply power to the same load at the same time (if required by the system). From a traditional perspective, these initial 48 V/12 V dual-battery DC-DC converter designs used different power components for step-down and step-up.

ADI’s PbL product department recently introduced a two-way DC-DC controller LT8228, which uses the same external power components as the step-down conversion for step-up conversion.

The LT8228 (shown in Figure 2) is a 100 V bidirectional constant current or constant voltage synchronous buck or boost controller with an independent compensation network. The flow direction of the power supply is automatically determined by the LT8228 or controlled externally. Input and output protection MOSFETs are used to prevent negative voltages, control surge currents, and provide isolation between terminals under fault conditions such as short-circuiting of switching MOSFETs. In the step-down mode, the MOSFET protection of the V1 terminal can prevent reverse current. In the boost mode, the same MOSFET controls the output surge current through an adjustable timer circuit breaker and protects itself.

New IC simplifies the design of 48 V/12 V dual-battery automotive systems  

Figure 2. The LT8228 in a simplified two-way battery backup system configuration

In addition, LT8228 also has bidirectional input and output current limiting and independent current monitoring functions. No master, fault-tolerant current sharing allows adding or deleting any parallel LT8228, while ensuring current sharing accuracy. Internal and external fault diagnosis and reports are available through the fault and report pins. The LT8228 is available in a 38-pin TSSOP package.

LT8228 is a 100V bidirectional peak current mode synchronous controller with MOSFET protection function. In the step-down mode, the controller provides a step-down output voltage V2 from the input voltage V1; or in the step-up mode, the input voltage V2 provides a step-up output voltage V1. The input and output voltage can be set up to 100 V. The working mode can be controlled externally through the DRXN pin, or automatically selected. In addition, the LT8228 can provide MOSFET protection for the V1 and V2 terminals. MOSFETs can prevent negative voltages, provide isolation protection between the input and output ports in the event of internal or external faults, and provide reverse current protection and surge current control. In applications such as battery backup systems, the bidirectional function allows the use of high-voltage or low-voltage power sources to charge the battery. When the power source is not available, the battery can provide the power source that has undergone a step-up or step-down process.

To optimize the transient response, the LT8228 uses two error amplifiers: EA1 in boost mode and EA2 in buck mode, with independent compensation pins VC1 and VC2, respectively. When the reverse Inductor current is detected under conditions such as light load operation, the controller works in discontinuous conduction mode. The LT8228 uses the following four pins for input and output current limit programming in buck and boost modes: ISET1P, ISET1N, ISET2P, and ISET2N. In addition, the controller uses the IMON1 and IMON2 pins to provide independent input and output current monitoring. In the entire input and output voltage range (0 V to 100 V), current limit programming and monitoring functions are valid.

In addition, the LT8228 can provide mainless, fault-tolerant output current sharing, and can be used for multiple parallel LT8228s to achieve higher load current, better heat dissipation management and redundancy. Each LT8228 can be adjusted to the average output current without the use of a main controller. When a single LT8228 is disabled or under fault conditions, it will stop outputting current to the average bus, making the current sharing solution fault-tolerant.

Other features include:

Feedback voltage tolerance: ±0.5% (within the full temperature range)

Two-way programmable current regulation and monitoring

Extended self-test, diagnosis and fault reporting

Programmable fixed or synchronized switching frequency: 80 kHz to 600 kHz

Programmable soft start and dynamic current limit

No owner, fault-tolerant current sharing

in conclusion

The LT8228 can improve the performance, control functions and simplify the design of the 48V/12V dual-battery DC-DC automotive system by using the same external power components for step-down and step-up. It can work in 48 V bus to 12 V bus buck mode or 12 V to 48 V boost mode as needed. When starting the car or requiring additional power, the LT8228 allows two batteries to supply power to the same load at the same time. Power conversion designers can use this versatile bidirectional converter to easily configure the 12V and 48V battery systems required by future fully autonomous vehicles.

author

  

Tony Armstrong

Tony Armstrong is the director of product marketing for ADI’s Power by Linear product group. He is responsible for all matters of power conversion and management of products from launch to discontinuation. Before joining ADI, Tony held various positions in marketing, sales and operations at Linear Technology, Siliconix Inc., Semtech Corp., Fairchild Semiconductors and Intel. He holds a Bachelor of Applied Mathematics (Hons) from the University of Manchester, UK. Tony will retire in the spring of 2020.

Introduction

The application of 48 V/12 V battery systems in the automotive field is just around the corner. In the past few years, most major automakers in the world have struggled to prove the applicability of their systems. At present, it is clear that these systems are expected to be implemented in the short term. This is a necessary and critical step in the long and arduous process of realizing unmanned and truly autonomous passenger vehicles. Nonetheless, this does not mean that 12 V batteries will be withdrawn from the market; this is unlikely to happen because there are too many old systems in installed vehicles. In other words, autonomous vehicles will use 12 V batteries and 48 V batteries at the same time.

 New IC simplifies the design of 48 V/12 V dual-battery automotive systems 

Figure 1. The new generation of cars will be powered by 12 V and 48 V batteries

This means that the internal system of the vehicle will use either a 48 V lithium ion (Li-Ion) battery or a 12 V enclosed lead-acid (SLA) battery, but both cannot be used at the same time. However, due to the chemical nature of these two batteries, in addition to designing two independent charging circuits for them, a mechanism must be used to allow charge to flow between them without causing any damage to the battery or any system in the car. Any damage. In addition, considering that one of the batteries fails during operation, the use of two batteries can provide redundant power.

Although this will certainly complicate the design of various electrical subsystems in the vehicle, there are also some advantages. According to some automakers, electrical systems based on 48 V can increase the fuel economy of internal combustion engine vehicles by 10% to 15%, thereby reducing carbon dioxide emissions. In addition, the future use of 48 V/12 V dual-system vehicles will allow engineers to integrate electric booster technology that operates independently of engine load, thereby improving acceleration performance. This type of electric supercharger is already in the advanced stage of development, and will be located between the bleed air system and the intercooler, using a 48 V voltage rail to rotate the turbine blades.

Globally, fuel economy regulations are becoming stricter, and networked autonomous driving functions are becoming more and more popular in new vehicles. Therefore, the 12 V automotive electrical system has reached the limit of its available power. At the same time, these changes do not seem to be enough, and the demand for automotive Electronic systems has also grown significantly. Coupled with related power requirements, these changes have created a whole new set of engineering opportunities. Obviously, the 12 V lead-acid battery automotive system with a power limit of 3 kW must be supplemented.

In addition, there are new automotive standards that affect how these systems work. The newly proposed automotive standard (called LV 148) combines the secondary 48 V bus with the existing automotive 12 V system. The 48 V power rail includes an integrated starter generator (ISG) or belt starter generator, 48 V lithium-ion battery, and a two-way DC-DC converter that can provide 10 kW of energy from 48 V and 12 V batteries. This technology is suitable for traditional internal combustion engine vehicles, hybrid vehicles and mild hybrid vehicles, and can help automakers meet increasingly stringent carbon dioxide emissions targets.

A new power solution for 48 V/12 V battery systems

This new standard requires the 12 V bus to continue to power ignition, lighting, infotainment, and audio systems. The 48 V bus will power the active chassis system, air conditioning compressor, adjustable suspension, electric supercharger/turbocharger, and even support braking energy recovery.

Adding a 48V power supply network to the vehicle is not without significant impact. The electronic control unit (ECU) will be affected and its operating range will need to be adjusted to a higher voltage. This requires DC-DC converter manufacturers to use dedicated ICs to achieve this high-power transmission.

Therefore, ADI’s Power by Linear? (PbL) product department has designed and developed some DC-DC converters that can achieve this energy conversion with very high efficiency, thereby minimizing heat dissipation design problems while saving energy. .

Obviously, this requires the use of a bidirectional buck and boost DC-DC converter between 12 V and 48 V batteries. This kind of converter can be used to charge any one of the batteries, and can allow two batteries to supply power to the same load at the same time (if required by the system). From a traditional perspective, these initial 48 V/12 V dual-battery DC-DC converter designs used different power components for step-down and step-up.

ADI’s PbL product department recently introduced a two-way DC-DC controller LT8228, which uses the same external power components as the step-down conversion for step-up conversion.

The LT8228 (shown in Figure 2) is a 100 V bidirectional constant current or constant voltage synchronous buck or boost controller with an independent compensation network. The flow direction of the power supply is automatically determined by the LT8228 or controlled externally. Input and output protection MOSFETs are used to prevent negative voltages, control surge currents, and provide isolation between terminals under fault conditions such as short-circuiting of switching MOSFETs. In the step-down mode, the MOSFET protection of the V1 terminal can prevent reverse current. In the boost mode, the same MOSFET controls the output surge current through an adjustable timer circuit breaker and protects itself.

New IC simplifies the design of 48 V/12 V dual-battery automotive systems  

Figure 2. The LT8228 in a simplified two-way battery backup system configuration

In addition, LT8228 also has bidirectional input and output current limiting and independent current monitoring functions. No master, fault-tolerant current sharing allows adding or deleting any parallel LT8228, while ensuring current sharing accuracy. Internal and external fault diagnosis and reports are available through the fault and report pins. The LT8228 is available in a 38-pin TSSOP package.

LT8228 is a 100V bidirectional peak current mode synchronous controller with MOSFET protection function. In the step-down mode, the controller provides a step-down output voltage V2 from the input voltage V1; or in the step-up mode, the input voltage V2 provides a step-up output voltage V1. The input and output voltage can be set up to 100 V. The working mode can be controlled externally through the DRXN pin, or automatically selected. In addition, the LT8228 can provide MOSFET protection for the V1 and V2 terminals. MOSFETs can prevent negative voltages, provide isolation protection between the input and output ports in the event of internal or external faults, and provide reverse current protection and surge current control. In applications such as battery backup systems, the bidirectional function allows the use of high-voltage or low-voltage power sources to charge the battery. When the power source is not available, the battery can provide the power source that has undergone a step-up or step-down process.

To optimize the transient response, the LT8228 uses two error amplifiers: EA1 in boost mode and EA2 in buck mode, with independent compensation pins VC1 and VC2, respectively. When the reverse Inductor current is detected under conditions such as light load operation, the controller works in discontinuous conduction mode. The LT8228 uses the following four pins for input and output current limit programming in buck and boost modes: ISET1P, ISET1N, ISET2P, and ISET2N. In addition, the controller uses the IMON1 and IMON2 pins to provide independent input and output current monitoring. In the entire input and output voltage range (0 V to 100 V), current limit programming and monitoring functions are valid.

In addition, the LT8228 can provide mainless, fault-tolerant output current sharing, and can be used for multiple parallel LT8228s to achieve higher load current, better heat dissipation management and redundancy. Each LT8228 can be adjusted to the average output current without the use of a main controller. When a single LT8228 is disabled or under fault conditions, it will stop outputting current to the average bus, making the current sharing solution fault-tolerant.

Other features include:

Feedback voltage tolerance: ±0.5% (within the full temperature range)

Two-way programmable current regulation and monitoring

Extended self-test, diagnosis and fault reporting

Programmable fixed or synchronized switching frequency: 80 kHz to 600 kHz

Programmable soft start and dynamic current limit

No owner, fault-tolerant current sharing

in conclusion

The LT8228 can improve the performance, control functions and simplify the design of the 48V/12V dual-battery DC-DC automotive system by using the same external power components for step-down and step-up. It can work in 48 V bus to 12 V bus buck mode or 12 V to 48 V boost mode as needed. When starting the car or requiring additional power, the LT8228 allows two batteries to supply power to the same load at the same time. Power conversion designers can use this versatile bidirectional converter to easily configure the 12V and 48V battery systems required by future fully autonomous vehicles.

author

  

Tony Armstrong

Tony Armstrong is the director of product marketing for ADI’s Power by Linear product group. He is responsible for all matters of power conversion and management of products from launch to discontinuation. Before joining ADI, Tony held various positions in marketing, sales and operations at Linear Technology, Siliconix Inc., Semtech Corp., Fairchild Semiconductors and Intel. He holds a Bachelor of Applied Mathematics (Hons) from the University of Manchester, UK. Tony will retire in the spring of 2020.

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Author: Yoyokuo