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DC/DC converters drive LEDs at constant current

Posted: 28 Mar 2007 ?? ?Print Version ?Bookmark and Share

Keywords:LED driver? DC/DC converter? lighting applications?

Linear Technology Corp. has announced two 40V, 4.5A DC/DC converters designed to drive high-current LEDs at constant current. The LT3478 and LT3478-1 have a 2.8-36V input range that's suitable for a wide variety of applications, including automotive, industrial and architectural lighting. In boost mode, both devices can drive up to six 700mA LEDs in series from a 12V input, making them suitable for applications such as automotive display backlighting.

True color PWM dimming
The LT3478-1 uses an internal current sense resistor, limiting output current to 1A, whereas the LT3478 uses an external sense resistor to extend the maximum LED current up to 4.5A. Both parts deliver efficiencies up to 90 percent in boost mode from a thermally enhanced TSSOP-16E package. The devices use true color PWM dimming, which delivers constant LED color with dimming ranges up to 3,000:1, and a 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 200kHz and 2.25MHz, optimizing efficiency while minimizing external component size.

These DC/DC converters sense output current at the high tide of the LED, enabling buck, buck-boost or boost configurations. One of the two CNTRL pins can be used to program maximum LED current and the other can be used to program a reduction in maximum LED current with increases in temperature, thereby maximizing LED usage and improving overall reliability. Other features include inrush current protection, open LED protection and programmable soft-start.

Availability, pricing
The LT3478EFE and LT3478EFE-1 are available from stock in a thermally enhanced 16-lead TSSOP-16E package. Both are priced at $3.60 each. Extended temperature versions, "I" Grades, the LT3478IFE and LT3478IFE-1, are also available from stock. Pricing for both versions starts at $4.32 each in 1,000-piece quantities.

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