LED driver has internal PWM generator

June 21, 2013 // By Graham Prophet
LT3955 is a DC/DC converter 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 suitable for driving high current LEDs, and it also has features 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. It 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 20W. 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 100 kHz and 1 MHz, optimising efficiency while minimising external component size and cost. In with a 5 x 6mm QFN package, the LT3955 offers a compact high-power LED driver solution.

The internal PWM generator delivers dimming ratios as high as 25:1 or it can use an external PWM signal, delivering dimming ratios of up to 3,000:1 with Linear's True Color PWM Dimming. For less demanding dimming requirements, the CTRL pin can be used to provide a 10:1 analogue 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 costs $3.75 (1000). An extended temperature version, or I grade, the LT3955IUHE, is also available, at $4.41.

Linear Technology; www.linear.com/product/LT3955