110-V LED controller offer spread spectrum frequency modulation benefits

September 20, 2013 // By Paul Buckley
Linear Technology has introduced a 110 V, high-side current sense DC/DC converter designed to regulate a current or voltage to a constant value, ideal for driving high brightness (HB) LEDs.

The LT3795's 4.5 V to 110 V input voltage range makes it appropriate for a wide variety of applications, including automotive, industrial and architectural lighting. The LT3795 uses an external low side N-channel MOSFET and can drive up to 90V of white LEDs from a nominal 12 V input, delivering in excess of 50 watts. Spread spectrum frequency modulation reduces EMI emissions, while an internal PMOS switch driver delivers robust short-circuit protection in boost and buck-boost topologies.

The LT3795 incorporates a high-side current sense, enabling it to be used in boost, buck, buck-boost or SEPIC topologies. Additionally it offers current both input and output current limiting and monitoring for added reliability and design flexibility. The LT3795 can deliver efficiencies of over 94% in boost mode, minimizing the need for external heat sinking. A frequency adjust pin permits the user to program the frequency between 100 kHz and 1 MHz, optimizing efficiency while minimizing external component size and cost. Combined with a thermally enhanced TSSOP-28 package, the LT3795 offers a compact HB LED driver or charger solution.

The LT3795 uses PWM dimming, which delivers constant LED color with dimming ranges of up to 3,000:1. For less demanding dimming requirements, the CTRL pin can be used to offer a 10:1 analog dimming range. Its fixed frequency, current mode architecture offers stable operation over a wide range of supply and output voltages. Robust open and short-circuit protection maximize overall system reliability, while C/10 detection optimizes both battery and SuperCap charging designs. Additional features include input and output current reporting, frequency synchronization, programmable UVLO and a programmable fault restart timer.

Availability and Pricing

The LT3795EFE is available in a thermally enhanced TSSOP-28 package. Pricing starts at $3.45 each. An extended temperature version or I grade, the LT3795IFE, is also available with pricing starting at $3.86 each. Finally, a high temperature, or H grade, the LT3795HFE is available, the pricing starts at $4.11 each. All