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HB LED driver enables green lighting for automotive apps

Posted: 24 Oct 2008 ?? ?Print Version ?Bookmark and Share

Keywords:high-brightness LED? LCD? HB LED driver?


Maxim Integrated Products has released the MAX16826 programmable, four-string high-brightness (HB) LED driver for white, RGB, and RGB-plus-amber LED configurations. Designed to enable the transition to green lighting technology in automotive applications, this device maximizes system flexibility and provides the lowest solution cost for backlight drivers.

The MAX16826 integrates a switching regulator controller, 4-channel linear current-source driver, ADC and I?C interface. The I?C interface allows dynamic programming of the output voltage to maximize power efficiency. It also allows manufacturers to program LED current for each string to accommodate LED binning variations, thereby reducing implementation cost.

MAX16826 is designed for backlighting automotive infotainment displays, automotive display clusters, industrial and desktop monitors, and LCD TVs. It is also well suited for adaptive front lights and low-/high-beam assemblies, as well as other solid-state lighting applications.

Green challenge
With the traction of green initiatives among consumers, OEMs are shifting from CCFLs to HB LEDs for automotive backlighting applications. HB LEDs consume less power, and they do not contain hazardous materials such as the mercury in CCFLs. Moreover, consumers benefit from the enhanced color reproduction and longer lifespans of HB LEDs.

Yet, HB LEDs also pose unique challenges, particularly when used in the harsh operating environment of automotive applications.

The top challenge is for designers to improve the price-to-performance ratio of HB LED solutions to make them cost competitive with CCFLs. Designers also need to integrate fault protection while maximizing conversion efficiency. Automotive LED applications require advanced thermal-management capabilities and lastly, with all of the electronics in today's automotive environment, designers must maximize the efficiency of the HB LED driver circuit to minimize energy consumption from the battery.

Cost-efficient solution
Specifically designed for automotive applications, the MAX16826 provides OEMs with a highly cost-efficient, scalable solution. The device's advanced programming features allow it to be used for multiple designs with minimal component changes. They also enable system manufacturers to accommodate LED binning variations, thereby reducing overall manufacturing cost.

The MAX16826 employs an architecture that allows dynamic programming of the switching regulator's output voltage and the LED current amplitude in each channel. An internal ADC measures the drain voltage of each HB LED string. It then makes the measurements available to an external MCU through an I?C interface for output-voltage optimization and LED fault monitoring.

Dynamic programmability allows the same driver circuit to be used for multiple projects by simply adjusting the LED current or voltage through the I?C interface. This capability eliminates the need for component changes and greatly simplifies production. Moreover, output-voltage optimization maximizes conversion efficiency by reducing the voltage drop across the linear drivers. Consequently, it also reduces power dissipation and heat in the display.

Whereas existing designs employ integrated MOSFETs for LED current regulation, the MAX16826 drives external MOSFETs for both the switching converter and LED current regulators. This unique approach allows the device to drive more HB LEDs per string and more LED current across each string, thus enabling designers to utilize the MAX16826 for multiple projects. It also improves thermal management, because heat is dissipated by more components, and over a larger board area.

Fault monitoring feature
The MAX16826 is able to detect and react to LED open- and short-circuit faults. Whenever a fault is detected, the IC triggers internal circuits, which immediately disable the faulty elements. This integrated fault monitoring protects the HB LED driver and the automotive electrical system from damage. In addition, the automotive electrical system can read the fault condition through the device's I?C interface, and react accordingly.

The MAX16826's advanced features enable designers to meet the high-reliability requirements of automotive applications, while minimizing external component count and, therefore, solution cost.

Additional features include cycle-by-cycle current limiting, output overvoltage protection, and overtemperature protection.

The HB LED driver also packs additional benefits. For enhanced flexibility, the switching regulator can be configured as a boost or SEPIC converter; the voltage across the driven LEDs can therefore be both higher and lower than the supplied input voltage. The MAX16826 also offers a programmable switching frequency (100kHz to 1MHz) to reduce EMI in noise-sensitive applications such as automotive displays. Additionally, each current sink features a direct-PWM input to enable independent LED-dimming control for each channel. Thus, designers can independently adjust the LED brightness for each color in RGB applications for optimum color control.

Designed for harsh operating environments, the MAX16826 is fully specified over the -40C to +125 C automotive temperature range. The device can withstand load-dump transients up to 40V, and can operate under cold-crank conditions. The MAX16826 is available in a thermally enhanced, 5mm x 5mm, 32-pin TQFN package. Prices start at $2.05 (1,000-up, FOB USA).

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