Backlight Driver Integrates Power Supply and Dimming Functionality

Freescale’s 34844 is a high-efficiency LED driver designed for use in LCD backlighting, measuring between 10” to 27“.

The 34844 integrates a boost converter that generates theminimumoutput voltage required to keep all backlight LEDs illuminated with the selected current. This produces high-efficiency operation.

The integrated boost feature self-clocks at a default frequency of 600kHz, butmay be programmed via I2C to 150kHz, 300kHz, 600kHz or 1.2MHz. Operating fromsupplies of 7V to 28V, the 34844 is capable of driving up to 160 LEDs in 10 parallel strings. Current in the 10 strings ismatched to within ±2%, and can be programmed via an I2C or SMBus interface.

The 34844 includes a PWMgenerator for LED dimming. LEDs can be dimmed to one of 256 levels, programmable through the I2C/SMBus interface. The PWMfrequency can be set from 100Hz to 25kHz, or can be synchronised with an external input. If not synchronised to another source, the 34844’s internal PWMrate outputs on its Clock pin. This enablesmultiple devices to be synchronised.

The 34844 also supports optical and thermal closed-loop operation. Additional features include protection against over-temperature, LED-short, LED open-circuit, over-voltage, over-current and under-voltage lockout conditions.

 

FEATURES Input voltage range: 7V to 28V <60V boost output voltage 3A integrated boost FET <50mA LED current per channel 90% efficiency 10-channel current mirror with ±2% current matching I2C/SMBus interface PWM frequency programmable from 100Hz to 25kHz

APPLICATIONS Monitors Notebooks GPS devices Displays

 

Freescale