Power

Boost DC/DC Converter Powers LCD Backlight and Camera Flash WLEDs in Smart Phones

8th March 2006
ES Admin
Semtech has announced the SC4505, an integrated boost (step-up) DC/DC converter for driving white LEDs in LCD backlight and camera flash applications in cell phones and PDAs.
The SC4505 features a 2A power switch with an adjustable output voltage of up to 28V to drive two strings of up to six LEDs per string using a single inductor. Each string features an independent user-selectable current source with the backlight string supporting up to 75mA and the flash string supporting up to 125mA. The high power level can accommodate high-current LEDs for brighter displays.

The device supports independent control of the backlight and flash functions through separate pins. Backlight dimming can be achieved through digital PWM control signals with a range of 50Hz to 50 kHz, which maintain peak LED current for maximum brightness. The camera flash string features a user-controllable flash timeout that reduces LED burn out. In addition, the flash can be set to 20% of maximum flash current (torch or spotlight mode) for continuous LED lighting.

The converter operates at a nominal switching frequency of 1MHz with an input range of 2.6V to 16V. Driving the LEDs in series results in excellent current matching for uniform lighting. The SC4505’s high operating frequency and higher integration reduces board space and BOM costs of the display/flash subsystem.

The SC4505 uses a regulation technique that optimizes its operation to seek the highest efficiency irrespective of load current in each string. This innovative power regulation technology adapts to the instantaneous power requirements of the system, reducing power dissipation while maintaining high efficiency.

The SC4505 can be used to drive up to 12 LEDs which makes it very flexible and suitable for driving backlight displays in devices such as PDAs, GPS devices, portable media players, and portable gaming consoles with 5-inch to 7-inch LCD displays. It comes in a 3x3mm, 16-pin MLPQ package that is lead

The SC4505 is available immediately in production quantities and is priced at $1.56 each in 1000-piece lots. Ordering code is SC4505MLTRT.


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