GaN HEMT driver chip NSD2017 helps solve LiDAR application challenges

Autonomous driving is an important development direction for the intelligentization of new energy vehicles , and LiDAR with strong perception capabilities is an indispensable hardware device for L2+ and above autonomous driving. Naxin Micro 's single-channel high-speed gate driver chip NSD2017 is designed for driving GaN HEMT (high electron mobility transistor ) in LiDAR transmitters , helping to meet various challenges in LiDAR applications.

1) Introduction to the structure of the LiDAR system

The laser radar used in autonomous driving usually adopts D ToF (Direct Time-of-Flight) ranging method, that is, distance measurement and map imaging are performed by directly measuring the flight time of the laser. The figure below shows the typical structure of a DToF laser radar system, in which the signal processing unit records the time when the laser transmitter emits a light pulse and the time when the laser receiver receives the light pulse, and can calculate the target distance based on the time interval and the speed of light.

Typical DToF LiDAR System

In order to achieve high resolution and wide detection range, laser radar requires extremely narrow laser pulse width, extremely fast laser pulse frequency and extremely high laser pulse power, which puts higher requirements on the performance of power switch devices in laser transmitters. Compared with traditional Si MOSFET , GaN HEMT has more superior switching characteristics and is very suitable for DToF laser radar applications. The performance of GaN HEMT depends on the high-speed, high-driving capability and high-reliability GaN gate driver chip. NSD2017, with its excellent product characteristics, gives full play to the advantages of GaN HEMT in laser radar.

2) NSD2017 product features

- Recommended operating voltage: 4.75V~5.25V

- Peak source sink current : 7A/5A

- Minimum input pulse width: 1.25ns

- Transmission delay: 2.6ns

- Pulse width distortion: 300ps

- Rise time @220pF load: 650ps

- Fall time @220pF load: 850ps

-Package : DFN6 (2mm*2mm), WLCSP (1.2mm*0.8mm )

- Meets AEC-Q100 automotive certification

- Non-inverting and inverting input pins can be used to generate extremely narrow pulse widths

- With UVLO and OTSD protection

NSD2017 Typical Application Block Diagram

3) NSD2017 key performance to meet the challenges of LiDAR applications

1. High current driving capability, supporting long-distance detection of LiDAR

The long-range detection capability of LiDAR enables autonomous vehicles to detect obstacles in advance and avoid them in time, thereby increasing the upper limit of autonomous driving speed. To achieve a longer detection distance, it is usually necessary to use a higher-power laser transmitter without damaging the human eye, which requires a higher-current GaN HEMT and a driver chip with higher driving capability. Nanochip's NSD2017 has a 7A peak source current and 5A sink current capability, which can be used to drive high-current GaN HEMTs, thereby generating high-peak laser power and achieving long-range detection.

2. Extremely narrow input pulse width, meeting the high ranging accuracy requirements of LiDAR

DToF LiDAR measures the distance by measuring the time interval between the emission and reception of pulsed lasers. However, if the reflected light pulses from two adjacent targets overlap, the system will not be able to distinguish the distance information of the two adjacent targets. In order to meet the requirements of centimeter-level distance resolution, LiDAR requires extremely narrow light pulse widths, usually as low as a few nanoseconds, with fast rising and falling edges. The minimum input pulse width of NSD2017 is typically only 1.25ns, and the on and off paths have excellent delay matching, with input-to-output pulse width distortion as low as 300ps. In addition, under a 220nF load, the typical rise time of NSD2017 is 650ps, and the typical fall time is 850ps, which is also conducive to generating narrower pulse lasers.

NSD2017 minimum input pulse width test, Ch1 is the input waveform, Ch2 is the output waveform

3. Small package and high-frequency switching to optimize LiDAR angular resolution and frequency performance

The angular resolution of the LiDAR indicates the angular difference between two adjacent laser points during the scanning process, and the point frequency indicates the number of laser points emitted per second in the three-dimensional field of view. Generally speaking, the smaller the angular resolution of the LiDAR, the denser the adjacent point clouds, and the higher the point frequency, the stronger the perception ability of the LiDAR. In order to achieve higher angular resolution and point frequency, the LiDAR needs to arrange more laser emitters, which puts higher requirements on the package size of the driver chip. NSD2017 automotive-grade chip Not only does it provide DFN (2mm*2mm) packaging, it can also provide a smaller WLCSP (1.2mm*0.8mm) package. NSD2017 supports a maximum switching frequency of 60MHz, and the typical transmission delay is as low as 2.6ns, which ensures that the system control loop has a sufficiently fast response time and is also conducive to improving the LiDAR point frequency performance.

NSD2017 transmission delay test, Ch1 is the input waveform, Ch2 is the output waveform

4. Strong anti-interference ability to ensure the safety and reliability of LiDAR

In laser transmitters, in order to quickly switch GaN HEMT, the gate series resistor outside the gate driver chip is usually set to zero; the peak source current and sink current of the gate driver chip will cause large jitters in the VDD and GND inside the chip through the chip package parasitic inductance and PCB parasitic inductance, which may cause the drive circuit to work abnormally. NSD2017 effectively filters out the high-voltage burrs generated by the driver circuit by optimizing the package parasitic inductance and integrating decoupling capacitors inside the chip , thereby improving the anti-noise capability. In addition, NSD2017 has over-temperature protection and under-voltage protection functions to ensure the safe and reliable operation of the laser radar.

4) Summary

The GaN HEMT gate driver chip NSD2017 has the characteristics of high switching frequency, low transmission delay, extremely narrow pulse width, low distortion, strong driving capability and anti-interference. It adopts a small-size automotive-grade package, which can help meet the various application challenges of LiDAR, improve perception capabilities and ensure its safe and reliable operation.