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LED controller uses true colour PWM dimming

Posted: 29 Sep 2008     Print Version  Bookmark and Share

Keywords:DC/DC converter  high current LEDs  PWM dimming  LED colour 

Linear Technology Corp. has announced the LT3756, a 100V, high-side current sense DC/DC converter designed to drive high current LEDs. Its 6V to 100V input voltage range makes it ideal for a wide variety of applications, including automotive, industrial and architectural lighting. The LT3756 uses an external N-channel MOSFET and can drive up to 20 1A white LEDs from a nominal 12V input, delivering in excess of 70 watts. It incorporates a high-side current sense, enabling it to be used in boost, buck, buck-boost or SEPIC and flyback topologies. The LT3756 can deliver efficiencies of over 94 per cent 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 or a thermally enhanced MSOP-16 package, the LT3756 offers a very compact 70-watt LED driver solution.

The LT3756 uses true colour PWM dimming, delivering constant LED colour with dimming ranges up to 3,000:1. For less demanding requirements, the CTRL pin can be used to offer a 10:1 analogue dimming range. Its fixed frequency, current mode architecture ensures 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 LT3756 are available. The standard LT3756 offers an Open LED Status pin, and the LT3756-1 replaces the Open LED Status pin with a frequency synchronisation pin.

Both the LT3756EUD and LT3756EUD-1 are available from stock in a 16-pin 3mm x 3mm QFN package. The LT3756EMSE and LT3756EMSE-1 are both available in a thermally enhanced MSOP-16E package. Pricing starts at Rs.124.73 ($2.90) each for the QFN package options and Rs.129.03 ($3.00) each for the MSOP-16E options. Also available from stock are extended temperature versions, or "I" grades, namely the LT3756IUD and LT3755IUD-1, with pricing starting at Rs.141.94 ($3.30) each, in 1,000-piece quantities. Similarly, "I" grade options of the MSOP-16 versions, the LT3756IMSE and LT3756IMSE-1 are priced starting at Rs.146.24 ($3.40) each in 1,000-piece quantities.





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