Linear Technology recently rolled out the LT3797, a triple-output DC/DC controller designed to drive three independent channels of LEDs.
Its fixed-frequency, current-mode architecture delivers constant, accurately regulated LED current over a wide range of supply and output voltages.
The chip’s 2,5 V to 40 V input voltage range with transient ride-through to 60 V makes it ideal for automotive applications, which must operate through cold crank, stop/start and load dump scenarios, as well as for a wide range of industrial applications.
Each of the LT3797’s channels can drive a wide range of LED power in either step-up, step-down or SEPIC topologies. In a boost configuration, it powers three channels of up to 90 V with LED currents in excess of 1 A, delivering over 250 W of power from a nominal 12 V input with efficiencies as high as 93%.
Each of the three channels is operated by an independent PWM signal, enabling them to be dimmed to ratios as high as 3000:1. Each channel also offers both robust open-LED and short-circuit protection in boost mode. A frequency adjust pin enables the user to program the frequency between 100 kHz and 1 MHz to optimise efficiency while minimising external component size.
The device is designed so that each channel can use the most suitable configuration to drive its LED string, whether step-up, step-down, SEPIC or a combination of these. Its high-side current sense enables each channel to be used in the same or different configurations while rail-to-rail current sense enables outputs from 0 V to 100 V, offering a wide range of design flexibility. Other features include over-voltage and under-voltage lockout, 20:1 analog diming via the CTRL pin, and external synchronisation.
The device’s thermally enhanced 7 x 8 mm QFN package provides a highly compact solution footprint for 20 W to 250 W LED applications. A special version (LT3797EUKG) is tested and guaranteed to operate with a -40°C to 125°C operating junction temperature.
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