DC773A: 1A @ 3.9V Max, 3 ~ 4.2 Vin, Buck/Boost

Demonstration circuit 773 is a synchronous buck-boost 1MHz Luxeon III white LED driver featuring the LTC3441 and LTC2050. The board is optimized for 3.9V LED forward voltage output at 1000mA load current and a single lithium-ion input voltage range of 3V to 4.2V. With its high frequency, synchronous buck-boost internal power switches, low quiescent current, 1MHz switching frequency and thermally enhanced package, the LTC3441 is a very versatile and powerful IC for driving Luxeon III LEDs that require both step-up and step-down capability from lithium-ion supplies used in very compact handheld solutions.

The LTC3441 1MHz switching frequency allows all of the components to be small, surface mount devices. The current-mode control topology creates fast transient response and good loop stability with a minimum number of external components. The LED pushbutton is used to manually turn on the LED. The SHDN terminal can be used to program pulses of light from an external source for certain flash applications. The DIM terminal can be used to program the LED for dimmer operation than 1A LED current using a external PWM signal. The optional MODE/SYNC terminal can be used to synchronize the LTC3441 clock with an external clock.

The LTC2050 is used to control a constant LED current at the output with the minimum amount of power dissipation in the sense resistor. The five-pin LTC2050IS5 is used for minimum components and minimum pins, but the LTC2050IS6 with a shutdown pin can be used for extremely low quiescent current. [1]

The LTC3441 and LTC2050 datasheets give complete descriptions of the parts including operation and applications information. The datasheets must be read in conjunction with this Quick Start Guide for demonstration circuit 773. The LTC3441 is assembled in a small 10-pin thermally enhanced package with exposed pad. Lumileds’ LXHL-PW09 Luxeon III LED emitter has an exposed pad slug for thermal enhancement. Proper board layout is essential for maximum thermal performance. The LXHL-PW09 datasheet is found on Lumileds website www.lumileds.com.