Automotive LED Headlight Solution Based on ST L99LD21

Automotive headlights can not only complete the function of lighting, but also adjust the lighting brightness and area according to the road conditions in a timely manner, which not only provides drivers with a good visual range, but also does not affect the vehicles in front and oncoming traffic, improving driving safety.

Compared with the traditional halogen headlights, LED headlights have the advantages of high light efficiency, long life, fast response time and small size. The small size of LED headlights allows the integration of a larger number of LED beads in the headlight to achieve a variety of shapes, lighting areas can be subdivided, and even pixel-level adjustable. LED prices are becoming increasingly affordable, making its application in cars gradually popular.

ST's headlight demo board uses two high-power LED driver chips L99LD21 to drive the headlight internal matrix high beam, low beam and a string of auxiliary steering corner lights; an ST automotive-grade 32-bit PowerPC architecture microprocessor SPC560D30L1 for control; and a high-side driver VN7140AS to drive the cooling fan.

In addition, in the headlight solution, ST can also provide a two-phase bipolar stepper motor driver L99SM81V, which is used to complete the adaptive adjustment of the headlights. The stepper motor of different dimensions precisely adjusts the angle of headlight illumination, and can realize the functions of follow steering and dynamic vertical adjustment.

The L99LD21 integrates a two-stage power conversion architecture within a single chip. A constant voltage output boost is used as a pre-stage to provide a stable DC voltage; two constant current outputs are used to drive the LED string. This cascaded power conversion architecture not only erases the battery voltage variation for the constant current source, but also provides a wide output voltage range for the constant current source.

The L99LD21 also integrates switching MOSFETs and current sensing functions in both Bucks, streamlining peripheral circuits, reducing cost and Layout difficulties, and reducing PCB space.

The L99LD21 also has a limphome mode, timeout watchdog and a direct input pin to support customers' functional safety design requirements. The L99LD21 also has a limphome mode, timeout watchdog and a direct input pin to support customers' functional safety design requirements.

Development Tools

L99LD21-ADIS Discovery Kit: Includes demo board and SPC5-based firmware and GUI.

L99LD21-ADIS Discovery Kit

L99LD21-ADIS demo board GUI

Application note: Help customers to understand and use L99LD21 deeply, including the calculation of typical parameters, the selection of peripheral devices, etc.

Application note

On-line tool: ST is developing an online tool to help customers quickly complete parameter selection, loop stability analysis, and thermal evaluation. Interested customers can contact ST's support staff for further information.

►Scene application diagram

Scene application diagram

►Display board photo

Display board

►Solution cube diagram

Solution cube diagram

►Core technology advantage

l Cascaded Boost-Buck architecture;
l software configuration interface, and limphome mode, etc. to meet the requirements of functional safety;
l Buck stage with hysteresis control topology for matrix LED headlamp applications;
l high level of integration and simple peripheral circuitry;
l Scalable family product planning.

► Solution Specifications

AEC-Q100 Qualified

-General

-ST SPI communication v4.1

-5.5 ~ 24v battery operating voltage range

-Load Dump Protection

- QFN40L 6x6 (wettable flanker) with exposed pad

-Timeout watchdog and limp home function

-Low standby current

-Additional sections

-Fixed frequency architecture, SPI programmable

-Peak current mode control