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Linear Tech DC/DC converter can drive four strings of 10 120-mA LEDs

Linear Technology has introduced the LT3599, a 45 V, 2.1 MHz DC/DC boost mode converter designed to operate as a constant current LED driver for up to 40 white LEDs. From a 12 V input, the device can drive up to four strings of LEDs, each with up to ten 120 mA white LEDs in series while delivering efficiencies up to 90%.

The LT3599’s multichannel capability and 3.1 V to 30 V input voltage range suits it for medium-sized TFT-LCD backlighting applications. It offers 1.5% LED current matching for uniform display brightness. Dimming ratios as high as 3,000:1 can be attained by using True Color PWM dimming, according to the company.

A programmable 200 kHz to 2.1 MHz fixed frequency operation and current mode architecture offers stable operation over a wide range of supply and output voltages while minimizing the size of the external components. The device’s switching frequency can be synchronized to an external clock for improved noise immunity.

The LT3599 uses a single 2 A, 45 V internal switch to provide a boost mode constant current source, and it will continue to regulate the LED current even when VIN exceeds VOUT. The internal boost converter uses an adaptive feedback loop to regulate the output voltage slightly higher than the required LED voltage for maximum efficiency. If any of the LED strings experiences an open circuit, it will continue to regulate the existing strings and signals the OPENLED alert pin. If higher current LEDs are required, multiple strings can be combined, enabling it to drive up to two strings of ten 240 mA LEDs. Additional features include LED current derating based on junction temperature and/or LED temperature and programmable overvoltage protection when all LED strings are disconnected.

The LT3599EUH is available in a 32-lead 5 mm x 5 mm QFN package and the LT3599EFE is offered in a TSSOP-28E. Prices start at $3.25 each and $3.35 respectively in 1,000-piece quantities. The LT3599IUF and LT3599IFE are tested and guaranteed to operate to the -40°C to 125°C operating junction temperature and are priced at $3.82 each and $3.94 each, respectively, in 1,000-piece quantities. All versions are available from stock.

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