Linear LED Driver Uses Step-Up DC/DC Controller

Linear Technology has announced the LT3760, an eight-channel LED driver that utilises a step-up DC/DC controller capable of driving up to a 45V string of 100mA LEDs per channel. Its internal 60V, 1MHz DC/DC boost mode controller is designed to operate as a constant-current LED driver for up to 80 white LEDs. From a 12V input, the LT3760 can drive eight channels, each with up to 10 100mA white LEDs in series, while delivering efficiencies exceeding 92 per cent.

Its multi-channel capability makes it suitable for medium and large-sized TFT-LCD backlighting applications. Its input-voltage range of 6 to 40V makes it suitable for automotive, avionic, HDTV and industrial display applications. The LT3760 offers +/-2.0 per cent (+/-0.7 per cent typical) LED current matching to ensure uniform brightness of the display. Dimming ratios as high as 3,000:1 can be attained by using True Color PWM dimming.

A programmable 100kHz to 1MHz fixed-frequency operation and current mode architecture offers stable operation over a range of supply and output voltages, while minimising the size of the external components. Additionally, the switching frequency is synchronisable to an external clock. Its thermally enhanced TSSOP-28 package offers a highly compact solution footprint for most LED backlighting applications. The LT3760 uses an external N-Channel MOSFET switch to provide a boost mode constant-current source.

However, even when VIN exceeds VOUT, the LT3760 will continue to accurately regulate the LED current. The internal boost controller uses an adaptive feedback loop to drive up to eight channels of 10 100mA LEDs, 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 circuit, the LT3760 will continue to regulate the existing strings and signal the Fault alert pin.

If higher current LEDs are required, multiple strings can be combined, enabling the LT3760 to drive up to four channels of 10 200mA LEDs or two channels of 10 400mA LEDs. Additional features include programmable LED current derating based on junction temperature and LED temperature, and programmable output voltage limiting when all LED strings are disconnected. The LT3760EFE is available in a thermally enhanced 28-lead TSSOP package. An industrial-grade version, the LT3760IFE, is tested and guaranteed to operate from a -40C to 125C operating junction temperature.

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