Linear Technology has introduced the LT3478 and LT3478-1, 40 V, 4.5 A dc/dc converters with a 2.8 V to 36 V input range designed to drive high-current LEDs at constant current. In boost mode, the LT3478/-1 can drive up to six 700 mA LEDs in series from a 12 V input in automotive display backlighting applications.
The LT3478-1 uses an internal current sense resistor, limiting output current to 1 A, while the LT3478 uses an external sense resistor to extend the maximum LED current up to 4.5 A. Both parts are said to deliver efficiencies up to 90% 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. A fixed-frequency, current-mode architecture offers stable operation over a wide range of supply and output voltages. A frequency adjust pin enables users to program the frequency between 200 kHz and 2.25 MHz, optimizing efficiency while minimizing external component size.
The LT3478/-1 senses output current at the high side 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.
The LT3478EFE and LT3478EFE-1 are available from stock in a thermally enhanced 16-lead TSSOP-16E package. Pricing starts at $3.60 each for both versions. Extended temperature versions, "I" grades, the LT3478IFE and LT3478IFE-1, are also available from stock. Pricing starts at $4.32 each for both versions in 1,000-piece quantities.