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LED driver boasts internal PWM generator

Posted: 24 Jun 2013     Print Version  Bookmark and Share

Keywords:Linear Technology  LED driver  PWM generator  DC/DC converter  LT3955 

Linear Technology has introduced a DC/DC converter intended to operate as a constant-current source and constant-voltage regulator with an internal 3.5A switch. The LT3955 has an internal PWM dimming generator that makes it ideal for driving high current LEDs, and for charging batteries and supercapacitors. The device’s 4.5-60V input voltage range also targets automotive, industrial and architectural lighting applications, added the firm.

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 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 more than 94 percent 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.

The LT3955 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 analog dimming range. Its fixed frequency, current-mode architecture offers stable operation over a 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 5 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.





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