The LT3955, a DC/DC converter designed to operate as a constant-current source and constant-voltage regulator with an internal 3.5A switch, is now available from Linear Technology. The device's internal PWM dimming generator makes it ideal for driving high-current LEDs, and is also suitable for charging batteries and supercapacitors. The LT3955's 4.5V to 60V input voltage range suits a wide variety of applications, including automotive, industrial and architectural lighting.
The LT3955 uses an internal 3.5A, 80V N-channel MOSFET and can drive up to twelve 300mA white LEDs from a nominal 12V input, delivering in excess of 20 watts. It incorporates a high-side current sense, enabling use in boost mode, buck mode, buck-boost mode or SEPIC topologies. The LT3955 can deliver efficiencies of over 94% in the boost topology, eliminating the need for external heat sinking. A frequency adjust pin permits the user to program the frequency between 100kHz and 1MHz, optimizing efficiency while minimizing external component size and cost. Combined with a 5mm x 6mm QFN package, the LT3955 offers a highly compact high power LED driver solution.
The LT3955 has an internal PWM generator that delivers dimming ratios as high as 25:1 or it can utilize an external PWM signal, delivering dimming ratios of up to 3,000:1. For less demanding dimming requirements, the CTRL pin can be used to provide a 10:1 analog dimming range. Its fixed frequency, current-mode architecture offers stable operation over a wide range of supply and output voltages. Output short-circuit protection and open LED protection enhance system reliability. The LT3955's ground-referenced voltage FB pin serves as the input for several LED protection features and makes it possible for the converter to operate as a constant-voltage source for charging applications.
The LT3955EUHE is available in a 36-lead 5mm x 6mm QFN package. Pricing starts at $3.75 each. An extended temperature version, or I grade, the LT3955IUHE, is also available, priced starting at $4.41 each. All pricing is based on 1,000-piece quantities and both versions are available from stock.