LED driver with internal PWM generator

June 20, 2013 // By Christoph Hammerschmidt
The LT3955 is a DC/DC converter from Linear Technology designed to operate as a constant-current source and constant-voltage regulator with an internal 3.5A switch. The device’s internal PWM dimming generator makes it ideal for driving high current LEDs, and it also has features suitable for charging batteries and supercaps. With a wide 4.5V to 60V input voltage range the LT3955’s 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. For more information, visit www.linear.com/product/LT3955.

For more information, visit www.linear.com/product/LT3955.