Simple buck-boost solution for LED drivers

Posted By : Alex Lynn
Simple buck-boost solution for LED drivers

The latest addition to Allegro MicroSystems’ family of 62xx/808xx LED drivers for lighting, has been announced. The ALT80802 addresses a key market trend of three to four White LEDs in a single string powered from 12V battery input, which is well suited for Fog, Backup, DRL, Side Mirror and other Automotive Lighting applications. 

The device can meet this requirement and provides two megahertz operation, enhanced performance in PWM dimming capability and fault protection, reducing the external component count. Furthermore, the ALT80802 can be operated in buck mode up to two amps, to drive one to two WLEDs from the battery or up to 12 WLEDs from a pre-boost supply.

The ALT80802 is a high-frequency switching regulator that provides constant output current to drive high-power LEDs. It is designed to aid in EMC/EMI design by frequency dithering, soft freewheel diode turn-off, and well controlled switch node slew rates. A programmable oscillator allows the device to switch up to 2.5MHz, outside EMI-sensitive frequency bands such as the AM band. 

It integrates a power MOSFET for step-down (buck) or inverting buck-boost conversion. The 50V-rated Enable pin can be tied to Vin for automatic startup, to support battery-level PWM dimming common in legacy body controllers. The wide input range of 3.8 to 50V makes the ALT80802 highly flexible.

With current-mode control and simple external compensation, the ALT80802 can achieve fast transient response. The control loop of the ALT80802 is designed for PWM dimming operation to achieve low dimming on-time, low turn-on overshoot, accurate PWM duty cycle, and wide dimming range. 

Extensive protection features of the ALT80802 include pulse-by pulse current limit, hiccup mode short-circuit protection, open/short freewheeling diode protection, BOOT open/short voltage protection, VIN under voltage lockout, and thermal shutdown. 

The ALT80802 is AEC-Q100 automotive qualified and is available in a small ten pin DFN package with thermal pad and wettable flank.


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