Quick guide to GaN FETs for LiDAR in autonomous vehicles
Designing a high-power and high-performance gate driver that meets the safety requirements of IEC 60825-1 using discrete components is complex and time consuming, potentially adding to cost and extending time to market. To meet these challenges, designers can turn to integrated, high-speed gate driver ICs paired with gallium nitride (GaN) power field effect transistors (FETs). Using an integrated solution minimizes the parasitics that degrade the integrity of the drive signal, particularly in the high- current laser power loop, and it enables locating the high-current driver close to the power switches, minimizing the effect of high- frequency switching noise.
This article provides a brief introduction to LiDAR. It discusses applications and safety requirements before reviewing the challenges of designing automotive LiDAR, focusing on the high-current laser power loop. It then presents LiDAR solutions from Efficient Power Conversion (EPC), Excelitas Technologies , ams OSRAM , and Texas Instruments, including GaN power FETs, gate drivers, and laser diodes, along with evaluation boards and implementation guidance to speed the development process.
How LiDAR works
LiDAR systems measure the round- trip time-of-flight (ToF) (Δt) of a laser beam pulse to calculate the distance from an object (Figure 1). The distance (d) can be calculated using the formula d = c * Δt/2, where c is the speed of light in air. Short pulse durations are one of the keys to LiDAR. Given that the speed of light is approximately 30 centimeters per ns (cm/ns), a 1 ns LiDAR pulse has a length of about 30 cm. This puts a lower limit of about 15 cm on the minimum feature size that can be resolved. As a result, LiDAR pulses must be limited to a few nanoseconds to have a useful resolution for human- scale environments.
Light detection and ranging (LiDAR) applications include autonomous vehicles, drones, warehouse automation, and precision agriculture. Humans are present in most of these applications, leading to concerns about a LiDAR laser’s potential to cause eye damage. To prevent injury, automotive LiDAR systems must meet IEC 60825-1 Class 1 safety requirements while transmitting at up to 200 watts. The general solution uses a pulse of 1 to 2 nanoseconds (ns) at a 1 to 2 megahertz (MHz) repetition rate. This is challenging as a microcontroller or other large digital integrated circuit (IC) is needed to control the laser diode but cannot directly drive it, so a gate driver circuit must be added. Also, this gate driver design must be optimized to ensure that the performance of the LiDAR system is suitable for Society of Automotive Engineers (SAE) Level 3 and higher advanced driver assistance (ADAS) systems.
By Kenton Williston Contributed By DigiKey's North American Editors
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