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DC/DC converter designed to drive high current LEDs

Posted: 11 Jun 2008     Print Version  Bookmark and Share

Keywords:DC/DC converter  high current LED  input voltage range  N-channel MOSFET 

controller

Linear Technology announces the LT3755, a 60V, high-side current sense DC/DC converter designed to drive high current LEDs. Its 4.5V to 40V input voltage range makes it ideal for a wide variety of applications, including automotive, industrial and architectural lighting.

The LT3755 uses an external N-channel MOSFET and can drive up to 14 1A white LEDs from a nominal 12V input, delivering in excess of 50 watts. It incorporates a high-side current sense, enabling it to be used in boost, buck, buck-boost or SEPIC and flyback topologies. The LT3755 can deliver efficiencies of over 94% in boost mode, eliminating any 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 3mm x 3mm QFN package, the LT3755 offers a very compact 50 watt LED driver solution.

The LT3755 uses True Colour PWM dimming, which delivers constant LED colour with dimming ranges of up to 3,000:1. For less demanding dimming requirements, the CTRL pin can be used to offer a 10:1 analogue dimming range. Its fixed frequency, current mode architecture offers stable operation over a wide range of supply and output voltages. A ground referenced voltage FB pin serves as the input for several LED protection features, making it possible for the converter to operate as a constant-voltage source.

Two versions of the LT3755 are available—the standard LT3755, which offers an Open LED status pin, and the LT3755-1, which replaces the Open LED status pin with a frequency synchronisation pin.

Both the LT3755EUD and LT3755EUD-1 are available from stock in a 16-pin 3mm x 3mm QFN package. Pricing starts at Rs.110.06 ($2.75) each for both versions in 1,000-piece quantities. Extended temperature versions, or "I" grades, namely the LT3755IUD and LT3755IUD-1, are also available from stock. Pricing starts at Rs.126.07 ($3.15) each, respectively, in 1,000-piece quantities.

LED controller

Summary of Features: LT3755/-1

  • 3,000:1 true colour PWM dimming

  • Wide Input Voltage Range: 4.5V to 40V

  • Output voltage up to 60V

  • Constant-current and constant-voltage regulation

  • 100mV high side current sense

  • Drives LEDs in boost, buck Mode, buck-boost Mode,

  • SEPIC or Flyback topology

  • Adjustable frequency: 100kHz to 1MHz

  • Programmable under-voltage lockout with hysteresis

  • Open LED status pin (LT3755)

  • Frequency synchronisation (LT3755-1)

  • PWM disconnect switch driver

  • CTRL pin provides analog dimming

  • Low shutdown current: <1uA

  • Programmable soft-start

  • Thermally enhanced 16-lead QFN (3mm × 3mm) package





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