What is an ADAS camera? Ultra-small PMIC automotive camera solution sharing

The advent of the era of autonomous driving and artificial intelligence has led to a shift in the research of automotive cameras from simply transmitting images to externally sensing and identifying the environment through algorithms, and internally enhancing driver status monitoring to enhance assisted driving functions. The high requirements of automotive perception systems have led to an increasing demand for high application performance of ADAS onboard cameras.

What is an ADAS camera?

The automotive ADAS (Advanced Driver Assistance Systems) camera group includes the most widely used front/surround view cameras, vision cameras for monitoring blind spots, rear view cameras for capturing reversing images, and built-in cameras for driver monitoring systems.

Currently, a car with ADAS function usually has more than 5 cameras, which work together for the car's 360-degree panoramic imaging, ranging, lane deviation, driving assistance and other functions.

As the core part of the visual algorithm in ADAS, the on-board camera has lower cost, higher dynamic observation and information transmission effect closer to vision than lidar. It can accurately identify objects and complement radar monitoring to reduce blind spots and improve driving safety.

As ADAS progresses from L2 to L3, the number of cameras in cars will increase and their applications will become more and more extensive. In addition to high requirements for sensors and processors, higher requirements are also placed on power management ICs. Therefore, low-power, high-efficiency, and small-package automotive camera PMICs will become a key development direction.

Ultra-small PMIC automotive camera solution

Silergy SA47302 is a power management solution developed based on automotive cameras. It has a wide input voltage of 4.0V to 16V (ABS 18V) and consists of a main DCDC Buck regulator, two secondary DCDC Buck regulators and a high PSRR low noise secondary LDO for powering the sensor, ensuring the stability and reliability of the power system.

The internal circuit structure of SA47302 is as follows:

SA47302

3-channel Buck, 1-channel LDO camera PMIC

◆ AEC-Q100 automotive certification

◆ 2.2MHz fixed switching frequency

◆ Support spread spectrum operation to improve EMI performance

◆ Internal integrated soft start function limits inrush current

◆ Main Synchronous Buck Regulator 1

-Fixed output voltage: 3.3V/3.8V

-Maximum continuous output current: 1.5A

◆ Secondary synchronous buck regulator 2

-Fixed output voltage: 1.1V/1.2V

-Maximum continuous output current: 1.5A

◆ Secondary synchronous buck regulator 3

- Fixed output voltage: 1.8V

-Maximum continuous output current: 1A

◆ Secondary LDO

-Output voltage: 2.8V/2.9V/3.3V

-Maximum output current: 300mA

◆ RoHS compliant and halogen-free

◆ Wettable flank package: QFN3x3-16, 0.5mm pitch

Timing control to ensure system stability

The power-on timing of SA47302 is controlled by the high/low voltage level of the SEQ pin, supporting the power-on timing of the buck converter and LDO of 2 power supply sequences. When VIN (PVIN1) is powered on and VIN is higher than the VIN UVLO_H threshold, the Gate Drive LDO (VCC) of the main Buck converter is turned on, and then the SEQ voltage level detection starts. When all channels complete the soft start and all channel outputs are stable, nReset is pulled high. When VIN is less than the VIN UVLO_F threshold, all outputs except VCC are powered off at the same time. VCC continues to be turned on to maintain all gate drivers and internal logic normally until VIN drops below 3.6V, thereby protecting the circuit safety and stability.

Spread spectrum function to improve EMI performance

In order to improve EMI performance, SA47302 uses a spread spectrum function to ensure that the minimum switching frequency is higher than 1.8MHz by expanding and jittering the switching frequency, thereby improving the product's EMI performance. The Buck2/3 converter uses a 180-degree phase shift operation to further reduce switching ripple and improve the EMI performance of the entire chip system.

Ultra-small package, providing a simple circuit board

With the development of ADAS and the improvement of the performance of vehicle-mounted cameras, the size of the performance module left for power supply is limited. Silergy SA47302 adopts QFN3x3-16 package, which provides a compact PCB layout, saving the circuit area of ​​the camera module to meet the miniaturization requirements of vehicle-mounted camera ICs.