Start-stop functionality is an expected feature in more and more new car models from any manufacturer. However, this presents a challenge in automotive electronics design, as starting the motor in cold weather can make the battery’s voltage drop as low as 3V. This is called a “cold crank.”
The power stage for most 12V automotive systems consists of a single buck converter that typically regulates the output voltage to 5V or 3.3V. Even if the regulator starts working in low-dropout mode, most circuits can be affected by a dip in the input voltage, and may stop functioning. The electronic control unit (ECU) always starts from the nominal battery voltage of 12V, and it is after start-up that cold-crank transients can occur. Using a pre-boost offers a solution to this problem.
This reference design will help engineers designing a pre-boost for a power supply up to 18W.