Integrated PWM waveform generation in CC/CV converter

April 19, 2013 // By Christoph Hammerschmidt
Linear Technology's LT3954 is a DC/DC converter designed to operate as a constant-current source and constant-voltage regulator with an internal 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 LT3954’s 4.5V to 40V input voltage range suits a wide variety of applications, including automotive, industrial and architectural lighting.

The LT3954 uses an internal 5A, 40V N-channel MOSFET and can drive up to eight 650mA 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 LT3954 can deliver efficiencies of over 95% 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, optimising efficiency while minimising external component size and cost. Combined with a 5 x 6mm QFN package, the LT3954 offers a highly compact high power LED driver solution.

The LT3954 has an internal PWM generator that 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. 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, with utput short-circuit protection and open LED protection. The LT3954'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 LT3954EUHE is available in a 36-lead 5 x 6mm QFN package.

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