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Step-down LED driver offers 10,000:1 true color PWM dimming

Posted: 24 Mar 2011 ?? ?Print Version ?Bookmark and Share

Keywords:step-down? DC/DC? converter? LED? driver?

Linear Technology rolls the LT3597 DC/DC converter designed to operate as a three channel, constant current LED driver. Each channel of the 60V, 1MHz, step-down converter contains a constant current sink LED driver with a dedicated adaptive-output buck converter.

This design offers maximum efficiency for applications, such as RGB displays, which require different output voltages for each LED string. From a 48V input, the LT3597 can drive up to three strings of LEDs, each with up to ten 100mA LEDs in series, delivering efficiencies of over 90 percent. The LT3597's multichannel capability and input voltage range of 6V to 60V makes it well suited for industrial, automotive and medical applications.

Each LED string can be independently programmed to deliver up to 100mA of LED current with 2 percent current matching between strings. Furthermore, each channel can be independently dimmed with True Color PWM dimming, offering dimming ratios as high as 10,000:1.

Linear's PWM dimming

A programmable 200kHz to 1MHz fixed frequency operation and current-mode architecture ensures stable operation over a wide range of supply and output voltages, minimizing the size of external components. Additionally, the switching frequency can be synchronized to an external clock. The LT3597's thermally enhanced 5mm x 8mm QFN package provides a highly compact solution footprint for LED lighting applications.

The LT3597 uses three independent 400mA, 60V internal switches to provide step-down constant current sources. The internal buck converters use 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 experience an open or short-circuit, the LT3597 will continue to regulate the other strings and signal the FAULT pin. Additional features include LED current derating based on junction temperature and/or LED temperature and LED disconnect in shutdown.

The LT3597EUHG is available in a 39-lead 5mm x 8mm QFN package. Pricing starts at $3.95 each in 1,000-piece quantities. An industrial grade version, the LT3597IUHG is tested and guaranteed to operate from a -40C to 125C operating junction temperature and is priced at $4.54 each in 1,000-piece quantities. All versions are available from stock.

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