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DC/DC converter drives up to 40 white LEDs

Posted: 27 Jan 2009     Print Version  Bookmark and Share

Keywords:boost mode converter  LEDs  LED driver  backlighting 

Linear Technology Corp. has introduced a 45V, 2.1MHz DC/DC boost mode converter designed to operate as a constant current LED driver for up to 40 white LEDs.

From a 12V input, the LT3599 can drive up to four strings of LEDs, each with up to ten 120mA white LEDs in series while delivering efficiencies up to 90%. Its multi-channel capability makes it ideal for medium-sized TFT-LCD backlighting applications.

The LT3599's input voltage range of 3.1V to 30V is well-suited for automotive, medical and industrial applications. The device offers 1.5% LED current matching to ensure uniform brightness of the display. Dimming ratios as high as 3,000:1 can be attained by using True Colour PWM dimming.

A programmable 200kHz to 2.1MHz fixed frequency operation and current mode architecture offers stable operation over a wide range of supply and output voltages while minimising the size of the external components. Additionally, the switching frequency is synchronisable to an external clock for improved noise immunity. The LT3599's thermally enhanced 5mm x 5mm QFN or TSSOP-28E package provides a highly compact solution footprint for LED backlighting applications.

The LT3599 uses a single 2A, 45V internal switch to provide a boost mode constant current source. However, even when VIN exceeds VOUT, the LT3599 will continue to regulate the LED current. The internal boost converter uses an adaptive feedback loop to regulate the output voltage slightly higher than the required LED voltage to ensure 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 240mA LEDs. Additional features include LED current derating based on junction temperature and/or LED temperature and programmable over-voltage protection when all LED strings are disconnected.

The LT3599EUH is available in a 32-lead 5mm x 5mm QFN package and the LT3599EFE is offered in a TSSOP-28E. 1,000-piece pricing starts at Rs.162.62 ($3.2)5 each and Rs.167.62 ($3.35) each, respectively. Industrial grade versions, the LT3599IUF and LT3599IFE, are tested and guaranteed to operate to the -40°C to 125°C operating junction temperature and are priced at Rs.191.14 ($3.82) each and Rs.197.14 ($3.94) each, respectively, in 1,000-piece quantities.

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