Constant-Current DC/DC LED Driver in ThinSOT

The LT1932 is a fixed frequency step-up DC/DC converter designed to operate as a constant-current source. Because it directly regulates output current, the LT1932 is ideal for driving light emitting diodes (LEDs) whose light intensity is proportional to the current passing through them, not the voltage across their terminals.

With an input voltage range of 1V to 10V, the device works from a variety of input sources. The LT1932 accurately regulates LED current even when the input voltage is higher than the LED voltage, greatly simplifying battery-powered designs. A single external resistor sets LED current between 5mA and 40mA, which can then be easily adjusted using either a DC voltage or a pulse width modulated (PWM) signal. When the LT1932 is placed in shutdown, the LEDs are disconnected from the output, ensuring a quiescent current of under 1µA for the entire circuit. The device’s 1.2MHz switching frequency permits the use of tiny, low profile chip inductors and capacitors to minimize footprint and cost in space-conscious portable applications.

Applications

* Cellular Telephones

* Handheld Computers

* Digital Cameras

* Portable MP3 Players

* Pagers

* Up to 80% Efficiency

* Inherently Matched LED Current

* Drives Five White LEDs from 2V

* Drives Six White LEDs from 2.7V

* Drives Eight White LEDs from 3V

* Adjustable Control of LED Current

* Disconnects LEDs In Shutdown

* 1.2MHz Fixed Frequency Switching

* Uses Tiny Ceramic Capacitors

* Uses Tiny 1mm-Tall Inductors

* Regulates Current Even When VIN > VOUT

* Operates with VIN as Low as 1V

* Low Profile (1mm) ThinSOT™ Package