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Since the first electric lighting was adopted in cars in 1898, the market demand for automotive electrical features and functions has been growing. As the limitations of 12V systems become increasingly apparent, the automotive industry is gradually turning to 48V systems. This shift is not only to provide greater power capacity and reduce the size of wires and connectors, but also to support more advanced electrical functions and effectively reduce energy consumption.
In current mild hybrid electric vehicles (MHEVs), two batteries are usually equipped: a 48V battery and a traditional 12V battery. Among them, the 48V-12V DC-DC converter plays a key role, connecting the two batteries to ensure the efficient operation of the power system. The 48V battery is mainly used to support the high performance requirements and energy-saving characteristics of the vehicle, while the 12V battery continues to be responsible for powering lower-power devices such as infotainment systems, engine control systems, and safety modules. This design not only ensures system compatibility, but also promotes the application and development of new technologies.
This article is the second part of the “48V-12V DC-DC Converter” system solution guide and will focus on the solution.
????DC-DC bidirectional converter based on non-isolated buck-boost topology
????Power Stage
The prevalent power stage topology in this application is a non-isolated synchronous buck converter. The synchronous switch also facilitates bidirectional current flow, enabling boost mode operation. From the 48V side, this configuration functions as a synchronous buck converter; from the 12V side, its functionality changes to a synchronous boost converter.
In 12V-48V vehicle systems, the battery is connected to the output of the DC-DC converter, which helps to reduce the output voltage ripple. To further reduce the output voltage ripple in boost mode, an LC filter is set on the 48V side. Another way to reduce the output voltage ripple is to spread the power over more interleaved phases. It should be noted that for both buck mode and boost mode, the LC filter may affect the stability of the converter. In addition, it is necessary to consider that the saturation current of the inductor must exceed the average DC current, and the capacitor must also meet the corresponding ripple current requirements in the design.
The bidirectional function has a significant impact on the selection of input and output capacitors. To achieve bidirectional operation, the capacitors inside the power stage dynamically switch functions. Selecting the output capacitor value is a trade-off between reducing output voltage ripple, overshoot, and system cost. Excessive output capacitance will also adversely affect transient response time.
Consider multiphase DC-DC bidirectional converters with up to six interleaved (parallel) power stages (phases). Multiphase converters are a logical choice for high-power applications, offering lower output ripple, smaller capacitors, and faster transient response compared to single-phase converters. Other benefits include smaller inductor size and improved power dissipation on the PCB.
The MOSFETs inside the power stage must withstand high currents and have a significant impact on the efficiency of the entire system. Conduction losses and switching losses together constitute the power dissipation in the transistor. The main parameters to consider are the on-resistance R DS(ON) , the gate charge, and the parasitic components, which can achieve a balance between conduction losses and switching losses.
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ON Semiconductor's new T10 technology for low and medium voltage MOSFETs is an ideal choice, featuring a shielded gate trench design with ultra-low QG and R DS(ON ) < 1mΩ.
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T10 technology reduces ringing, overshoot and noise through its industry-leading soft recovery body diode (Qrr, Trr), achieving the perfect balance between performance and recovery characteristics.
Component redundancy in 48V systems
Component redundancy in 48V power networks is critical to ensuring the reliability and resilience of power systems. In the event of a single component failure, redundant components can serve as a backup to prevent the entire system from being disrupted. This is especially important for critical safety systems such as those controlling brakes, steering, and airbags. The in-vehicle environment presents a variety of challenges, including vibration, temperature fluctuations, potential component failures, and short circuit risks.
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Redundancy helps improve the overall robustness of the vehicle's electrical architecture, ensuring continuous and uninterrupted functionality in the event of component failure, accidental damage, and reducing the risks associated with electrical shorts.
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Moving to a 48V architecture can accelerate the adoption of ADAS and higher-level autonomous driving features, such as steer-by-wire and brake-by-wire, where the requirements for redundancy, fault tolerance, and reliability are critical. Redundant drives for these high-peak load devices become lighter and more cost-effective with 48V systems than with 12V systems.
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A redundant 48V power bus with redundant switches prevents faults from propagating from one power bus to another. This ensures that if a part of the system fails, critical functions can be seamlessly transferred to the unaffected path.
Table 1 shows some of ON Semiconductor's devices that can improve the robustness and reliability of 48V electrical architectures by building redundant networks. The subsequent chapters of this System Solutions Guide describe each of the recommended devices.
????Integrated Automotive Power Modules (APMs) for 48V and MHEV Applications
ON Semiconductor offers a family of automotive MOSFET modules in a variety of packages designed for power applications in 48V systems, MHEVs and low-voltage traction systems.
The release of the APM21 module further enriches ON Semiconductor's high-performance, high-reliability transfer-molded module product line for automotive applications.
The APM series offers highly integrated compact designs with low stray inductance and better electromagnetic interference (EMI) performance. Efficient current handling eliminates the need for high current paths in the PCB.
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The NXV10V160ST1 APM21 integrates 6 100V MOSFETs (3x half-bridge) and can handle 3-phase typical applications such as 48V inverters, electronic compressors and other high-power auxiliary equipment.
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APM19 Modules: The FTC03V85A1 is an 80 V low R DS(ON) module with an optimized 3-phase MOSFET bridge that can be used to build a 1.5kW 48V-12V interleaved DC-DC converter. Two modules can form a 6-phase 3kW converter.
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The NXV08V110DB1 is an 80 V low R DS(ON) APM19 module optimized for use as a three-phase inverter bridge for variable speed motor drives.
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The APM19 module includes a precision shunt resistor for current sensing, an NTC for temperature sensing, and an RC snubber circuit.
The APM17 module is configured as a dual half-bridge (two-phase module) which can be easily externally connected to form a single half-bridge for twice the phase current.
AMP17 examples: NXV08H250DT1, NXV08H400EXT1. Three APM17 modules can be configured together to drive a three-phase motor or a six-phase motor (48V main inverter).
✦Low stray inductance: APM17 enables a total stray inductance of less than 15nH for a 25kW 48V inverter system.
✦Lowest junction-to-well thermal resistance.
✦Compact design with low total module resistance.
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Efficient high current handling, no high current paths required on the PCB.
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For 20~25kW, 24~36 MOSFETs can be reduced to 3 APMs.
✦The series offers insulating ceramic DBC substrate options to provide standard and premium thermal performance.
✦Various R
DS(ON)
ratings are available to meet the end user's current requirements, and a variety of pin-out options are available for different system designs.
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Package types: standard, press-fit, PCB side mounting pins.
The NXV08B800DT1 is an automotive dual-channel back-to-back MOSFET power module, 80V, 0.58mΩ, with common source connection. It works well as a battery or load switch in 48V MHEV applications (as shown below).
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Low junction-well thermal resistance.
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Optimized stray inductance and highly integrated compact design.
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Suitable for bidirectional systems, input path isolation.
????Disconnect Switches in DC-DC Converters
Each side of the DC-DC converter should have the ability to be disconnected from the respective power rail via a disconnect switch (circuit breaker). The best solution is a dual back-to-back N-MOSFET configuration, although only a single MOSFET is required on the 48V side.
ON Semiconductor MOSFETs with low R DS(ON) and rated voltages ranging from 40V to 100V meet the above requirements and minimize conduction losses in the power path. The disconnect switch should also provide overvoltage and overcurrent protection for the converter. The protected side of the 48V/12V disconnect switch can be used as a reference point for the voltage sensing circuit.
Designers can choose from a variety of component technologies that offer different characteristics. 80V to 100V MOSFETs can be used in converter power stages, 48V auxiliary equipment , and other applications. For 12V rails and traditional 12V applications, 40V low-voltage MOSFETs provide good performance.
????T10 Shielded Gate Trench Technology
The new T10 shielded gate trench technology is mainly targeted at DC-DC conversion applications (T10S model) and motor control and load switching (T10M model). The technology is designed to optimize efficiency, reduce output capacitance and key performance indicators, while achieving lower on-resistance R DS(ON) and gate charge QG. Among them, the outstanding 40V trench technology product NVMFWS0D4N04XM has an R DS(ON) as low as 0.42mΩ and adopts a compact 5x6 package. For the 80V option NVBLS0D8N08X, R DS(ON) can be as low as 0.79mΩ.
Compact package of 5.1 x 7.5 mm.
The NVMJST2D6N08H 80V version has a minimum R DS(ON) of 2.8 mΩ.
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Top Cool technology allows both sides of the PCB to be utilized, thus achieving higher power density.
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Reduce PCB temperature and extend system life.
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Improves heat dissipation by avoiding the heat conduction path of the PCB.
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Leaded package (gull-wing leads) enhances board-level reliability.
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Copper clip connection to minimize package resistance.
????T10 MOSFET Technology: Medium Voltage 80V and Low Voltage 40V
The new T10(S) shielded gate trench design is suitable for DC-DC conversion (switching applications) and is designed to optimize efficiency, low output capacitance and FOM factor. Compared to the traditional T8 trench gate technology, T10 achieves:
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Lower R DS(ON) and gate charge QG, R DS(ON) < 1mΩ, QG <10 nC.
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Lower Rsp (R DS(ON) vs area)
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Improved FOM (R ds x Q oss /QG/Q gd ) to increase performance and overall efficiency.
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Industry-leading soft recovery body diode (Qrr, Trr) reduces ringing, overshoot and noise.
In addition to DC-DC converters, they can also be used in a variety of 48V applications such as battery switching, auxiliary equipment (HVAC, e-turbocharging), PTC heaters, starter-generators.
characteristic:
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Drain-Source Desaturation Detection with Soft Shutdown
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Built-in charge pump supports 100% duty cycle operation (FAD3171MXA only)
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With undervoltage lockout protection (UVLO) protection, bidirectional fault indication pin
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Capable of handling negative transients up to -80V, fast load transition dVs/dt immunity exceeding ± 50 V/ns
Design Resources:
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Application Note AND90251/D
: FAD3151MXA and FAD3171MXA Schematics, Examples, and Circuit Analysis
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Tutorial
: General Purpose Isolation and Gate Driver Overview
????High-side and low-side drivers for DC-DC conversion
The NCV51513
and
NCV51511
are high-side and low-side gate drivers designed for automotive applications with high drive current capability and multiple configuration options, optimized for DC-DC power converters and inverters. These drivers are designed to drive MOSFETs in half-bridge or synchronous buck configurations.
The NCV51513 has best-in-class propagation delay, low quiescent current and low switching current at high frequency operation. It is available in two versions with different propagation delay times. The typical propagation delay of the version with filter is 50 ns, while the typical propagation delay of the version without filter is 20 ns. It has a dV/dt immunity of up to 50 V/ns, and the rise/fall times are 9 ns and 7 ns respectively for a 1 nF load.
????Electronic Fuse (eFuse) NIV3071 NIV3071 is an 8V to 60V, 10A electronic fuse (eFuse) that uses a small 5x6mm package and integrates 4 independent channels (2.5A per channel).
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It can drive 4 independent 2.5A loads, or short the eFuse outputs together to carry independent 10A continuous load current within 48V.
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Protects 12V and 48V downstream loads from output short circuit, overload, and overcurrent events.
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Applicable to automotive regional control units (regional control architecture), ensuring that local ECUs throughout the vehicle are protected and remain robust.
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Protecting 48V automotive body control modules, ADAS domain controllers, telematics, wiring harness protection.
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Soft-start, configurable current limit, control and status monitoring pins
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The evaluation board NIV3071MTW4GEVB supports prototyping and testing.
????NCV12711 - 12V Auxiliary Power Supply - Peak Current PWM Controller The NCV12711 is a fixed frequency, peak current mode PWM controller with the necessary performance to implement single-ended power converter topologies (flyback, forward converters). It has a wide 4-45V input range and can be used as a DC-DC controller for auxiliary power supplies.
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Operating frequency 100kHz to 1MHz, with slope compensation (to prevent subharmonic oscillation and improve EMI).
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1A source/sink gate driver. No auxiliary winding required.
Input voltage supports undervoltage lockout (UVLO), overpower protection, and programmable soft-start. -
Evaluation board NCV12711FLOATGEVB : 12V/1A primary side regulation, no auxiliary winding required.
Typical applications for isolation: PWM control, MCU interface, programmable logic control, data acquisition systems, voltage level conversion.
The "48V-12V DC-DC Converter" System Solution Guide also lists the corresponding ON Semiconductor products in detail. Scan the QR code below to get the full guide.
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