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LED Drivers for Boost, Buck or Buck-Boost High Current LED Applications

20th March 2008

ES Admin

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Linear Technology has announced the LT3517 and LT3518. They are both 45V, high side current sense DC/DC converters designed to drive high current LEDs. Their 3V to 30V input voltage range (with transient protection to 40V) makes them ideal for a wide variety of applications including automotive, industrial and architectural lighting. The LT3517 and LT3518 are identical except for switch current limits. The LT3517 has an internal 1.3A switch, whereas the LT3518 has an internal 2.3A switch.

The LT3518 can drive up to ten 350mA white LEDs from a 12V input, whereas the LT3517 can drive five, making them ideal for a variety of applications such as automotive display backlighting. Both parts can deliver efficiencies up to 90% in boost mode from a compact 4mm x 4mm QFN package. They utilize True Color PWM dimming to deliver constant LED color with dimming ranges of more than 3,000:1. For less demanding dimming requirements, the CTRL pin can be used to offer 10:1 analog dimming. Their fixed frequency, current mode architecture offers stable operation over a wide range of supply and output voltages. A frequency adjust pin enables the user to program the frequency between 250kHz and 2.5MHz to optimize efficiency while minimizing external component size.

The LT3517 and LT3518 sense output current at the high side of the LED, enabling buck, buck-boost or boost configurations. Other features include open LED protection, a gate driver for PMOS LED disconnect, and soft-start.

The LT3517EUF and LT3518EUF are both available from stock in 16-pin QFN package, priced starting at $2.70 and $2.95 each respectively in 1,000-piece quantities. Extended temperature versions, or I Grades, LT3517IUF and LT3518IUF, are also available from stock.