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Look Closer at Automotive Power Supplies

Changes in the nature of automotive power supply system design have accelerated in the last few years. This is based on several paths of development in auto electronics including:

  • The evolution from electromechanical to electrical-based functionality, particularly in body systems
  • Advances in powertrain design, including both greater efficiency of combustion engines and electrification/hybridization
  • Proliferation of Advanced Driver Assist Systems (ADAS)

This post is the first in a series that will examine developments in power supply ICs that present opportunities for engineers to keep pace with these changes and improve overall system reliability and efficiency. We’ll review applications of voltage regulation ICs and multi-output power supplies, as well as system basis chips (SBCs) with higher integration. All of these are generally responsible for conversion of a vehicle’s battery-sourced DC power to the steady and stable supply voltages required by sensors and system ICs such as microcontrollers and transceivers. Multi-output system supplies drive multiple devices with fail safe functions and monitoring capabilities, and SBCs also integrate one or more communications interfaces and switches.

Voltage regulators are the most frequently used electronic power supplies in automotive applications. For a broad line supplier such as Infineon the portfolio of automotive qualified linear voltage regulators includes more than 300 devices when accounting for package types. Commonly used in applications carrying up to 200 mA current loads, they are used in powertrain, transmission, instrumentation and lighting, as sensor supplies and in ADAS. Introduced for automotive applications in the early 1990s, multiple variants of the linear voltage regulator, or LDO, have been developed. These include simple voltage trackers and linear post regulators, devices that integrate a LIN transceiver and LDO, and high performance and application specific devices.

With increased demands on total system power available from a 12V main battery, reduced current consumption is a major objective in supply design. At a general level, LDOs address the need for higher efficiency with updates to underlying technology to improve spec sheet parameters such as quiescent current while achieving size reductions that allow for smaller package size. Improved robustness and wider input voltage V(in) ranges support more rigorous electrical standards and reliability in cranking applications, including increasingly common stop/start systems which may require stable output from inputs as low as 2.75-3V. In general, higher efficiency and higher reliability technologies are first employed for high performance devices, such as the TLS8xxx voltage regulator family. Versions of this device family are optimized either for low quiescent current (5µA with 250mV dropout) or ultra-low dropout (70mV with 40µA).

For sensor technologies, including under the hood sensors and the new generation of camera/radar sensor technologies, power supply architecture is often implemented as a two-stage solution. Voltage regulator variants well-suited to these applications include trackers and post regulators.

Voltage trackers are specifically designed to supply sensors and other off-board loads, with an emphasis on providing highly accurate output while protecting other system components from potential circuit disruptions. They are not a true voltage regulator, as they get an initial reference signal from an external source that typically is used to provide V(in) to multiple trackers. (Figure 1: LDO and Voltage Regulator Circuit Applications). Trackers distribute thermal dissipation, which is useful in designs with multiple on board components. They also include integrated protection features to buffer electrical events that lower risk of damage to a system microcontroller (MCU).

Figure 1

Click here for larger image 
LDO and Voltage Regulator Circuit Applications

LDO and Voltage Regulator Circuit Applications

Post regulators are an increasingly popular component in design of power supplies such as those used to drive the camera or radar sensor array in ADAS. They work in tandem with a DCDC main supply IC that acts as a pre-regulator and feeds 5V to post regulators for additional devices or loads, e.g. 3.3V for I/O devices, 2.5V to drive a camera, and 3.3V for a system MCU. The more efficient conversion of the switching pre-regulator and precise output of the post devices can increase efficiency of the overall system by 50-80%.

DCDC switching regulators are typically used in applications requiring output current above 500mA. While switching regulators require more costly external components to implement, the benefit is higher efficiency. DCDC regulators commonly offer fixed 5 and 3.3V outputs and options to adjust output to support specific component requirements. Input voltage ranges also support a wide range of system applications, from 4.5 V up to the 40V. As noted earlier, switching regulators also are the technology of choice in high current applications.

Systems supplies integrate switch-mode pre-regulators, LDOs and trackers or switch-mode post-regulators to convert battery output to drive multiple loads (Block Diagram: System Supply). In a supply to drive an MCU and associated sensors, a system supply IC uses its pre-regulator stage to efficiently generate 5.8V/1.3A. Three post regulators drive the MCU and peripherals while two trackers push 5V supplies off-board (Figure 2: System Supply IC). This class of devices also includes safety-related peripherals and independent controllers for ASIL-D qualified development.

Figure 2

System Supply IC

System Supply IC

System Basis Chips (SBCs) represent the highest level integration of power supply IC for automotive applications, adding rich communications support in the form of CAN and LIN transceivers, as well as high-side switches. This can lead to as much as an 80% reduction in board area for the power supply and communication functional blocks of an MCU-based design. Applications include body, climate and light control lights as well as gateways.

The diverse options available for power supply design reflect the multiple requirements of automotive electronics, with output current demands that range from 50mA to as much as 10A. System complexity also is a huge variable as designs range from straightforward single-channel to multi-channel and output power levels. And of course the pressure to accelerate design cycles, manage system power demands and constantly improve safety present ever larger challenges. In future posts, we’ll look more closely at typical applications for each class of power supply and consider how the accelerated pace of change in areas such as xEV and active sensing of the driving environment impact the evolution of automotive power supply.

Authors:

Vikram Patel, Product Manager, Infineon Technologies

Andres Zavala Sanchez, Segment Marketing Manager, Infineon Technologies

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