Automotive Battery Power Regulated with Buck / Boost ICs

Regulators are common circuit blocks used to make distinct power rails for specific circuit blocks in electronics. This usually occurs when the power supply into the design is either too high or too low for downstream circuits in the design. Regulator topologies vary but common types for low-power DC are bucks, boosts, and low-dropout. Low-power DC is commonly used in mixed-signal designs accommodating high-frequency transmissions.

Topologies include either linear or switching regulators. Linear regulators are simpler although inefficient, losing much of the regulated power to heat. On the other hand, buck regulators require few components and retain much of the regulated power, making them more energy efficient. For these reasons, a switching buck regulator is often employed to provide power for downstream circuit blocks in low-power, mixed-signal designs.

Switching regulators may either boost power to a higher rail or buck power to a lower rail. The topology uses feedback to regulate the output by changing the output duty cycle. The switch action is produced as a result of the output feedback response activating a switch. The switch is a fast-acting transistor responding to energy storage in the circuit topology’s output filter.

As in many circuit applications, the automotive industry has specific design requirements that affect the regulators used within it’s functional blocks. For automotive regulator ICs and their biasing discretes, the gating requirement is ability to work with the car’s battery power delivery system and limitations.

Let’s take a look at some considerations when choosing automotive regulator ICs.

Defining Characteristics of Buck and Boost Regulators

Regulators used in automotive applications require ability to work in harsh automotive environments. The car battery undergoes swings in power from it’s nominal 12V operating rail from as low as 2V and up to 42V. This means any regulator must be able to hold up under large swings from the supply.

Regulator ICs power dashboard applications

In addition, regulator ICs undergo large demands from downstream components or circuit blocks that can stress the battery. The regulator ICs must manage swings in power demands without generating large energy spikes. Avoiding generation of energy spikes avoids power drop-out to functioning circuits while at the same time avoiding injection of noise.

Given demands made for power sources, protections for inrush currents or short-circuit conditions must also be designed into the parts. Included for safety include tolerance to thermal events that can damage parts by having shutdown mechanisms should such events occur. Whatever the power provided or the packaging containing the regulator, there are many designed specifically for automotive applications.

Selecting a Buck or Boost Regulator for Automotive Designs

As always, regulator ICs come in many different shapes and sizes, and this holds true for automotive regulator ICs. There are many to choose from. Most of the choices involve number of down-regulated outputs, total power delivered, and hold-up feature. It is always best to determine your circuit needs before beginning the search for parts, as this will help narrow your search.

The parts we review, below, are all suitable for automotive applications, but they have unique characteristics that distinguish their delivered functionality. The first produces four outputs and would be useful for a circuit that requires separate voltage rails. The fourth output is a boost specifically included to provide holdup for your automotive battery in cold startup conditions. The second provides one output with holdup feature and the third is a simple buck with no backup feature for supply dropout.

Analog Devices, LT8603

This is a feature-rich regulator IC with ability to create three DC outputs bucked from an automotive battery input. The two high-power rails supply 5V and 3.3V, while a three output draws from one of the buck outputs to further down-regulate to 1.2V. The onboard boost regulator is purposed to provide hold up when the car’s battery falls below 8V, a common occurrence during cold startups in harsh environments. The IC has both a reset and an enable pin to allow minimal control interface.

The LT^®8603 is a highly flexible, quad output regulator combining two high input voltage capable monolithic step-down switching regulators, one low input voltage capable monolithic step-down regulator, and a boost controller to satisfy a wide range of applications while occupying minimal board space.

LT8603 Buck/Boost performance at cold startup Found on page 1 of LT8603 datasheet

Several configurations are available to maximize added features of the LT8603, and two evaluation boards are available, the DC2114A and the DC2469A, to try variations at the bench. In addition, the part was designed so that the two high-power buck outputs regulate from clocks 180° out of phase from each to balance peak inrush currents. Switching in opposite phase reduces contributions from transients during switching of the bucks and so avoids creating EMI to your circuits.

Texas Instruments, TPS65320D-Q1

This part provides one buck regulator output and one LDO output. The buck provides robust power of 3.2A driven from a programmable buck output of between 1.1V to 20V. The LDO sources from either the car battery, or if unavailable, switches its source from the buck output. Several enable pins allow outside control of either the buck or LDO outputs, while the IC has internal protection controls for soft start, current limit, thermal sensing, and shutdown to prevent damage to either the part or the overall system.

The TPS65320D-Q1 device is a combination of a high-VIN DC-DC step-down converter, referred to as the buck regulator, with an adjustable switch-mode frequency from 100-kHz to 2.5MHz, and a high-VIN 280-mA low-dropout (LDO) regulator. The input range is 3.6V to 36V for the buck regulator, and 3V to 36V for the LDO regulator. The buck regulator has an integrated high-side MOSFET. The LDO regulator features a low-input supply current of 45-µA typical in no-load, also has an integrated MOSFET with an active-low, push-pull reset output pin. The input supply of the LDO regulator auto-source from the output of the buck regulator when it is in operation. Low-voltage tracking feature enables TPS65320D-Q1 to track the input supply during cold-crank conditions.

TPS65320D-Q1 application and efficiency Found on page 1 of TPS65320D-Q1 datasheet

Given its ability to provide high power, the part is commonly used in automotive infotainment or radio head unit applications, in advanced driver assistance systems, and for automotive telematics or eCalls. To investigate loading when used within your system, there is an evaluation board, the TPS65320C-EVM that may help characterize its features at the bench.

STMicroelectronics, A5974AD

If either of the above-two parts have features that won’t be used in your application, take a look at the A5974AD offered by ST Microelectronics. This part is compact and offers one bucked output from the automotive battery. It is able to output 2A of current with output voltage adjustable from 1.235V to 35V.

The A5974AD is a step-down monolithic power switching regulator with a minimum switch current limit of 2.5A. It is therefore able to deliver up to 2A DC current to the load depending on the application conditions. The output voltage can be set from 1.235V to 35V. The high-current level is also achieved thanks to a HSOP8 package with exposed frame, that allows to reduce the RTHJ-A down to approximately 40℃/W.

Application schematic Found on page 1 of A5974AD datasheet

This part is built to qualify to AEC-Q100 quality requirements for use in the automotive industry. As with most regulator ICs, it provides current limit, low drop-out compensation, and thermal shutdown. It runs on a fixed frequency and has a pin that may synchronize it’s operation to an outside controller such as a PMIC.

No matter your need for automotive regulator ICs, our website lists all available along with sourcing and comparative costing information. Our website offers help with selecting, including lists of similar parts at the bottom of each part webpage. This helps for those afternoons when you’ve spent several hours searching for the right part but have need to hone your search without delay.

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