Features

• True Color PWM Delivers Constant Color with 400:1 Dimming Range
• Wide Input Range: 4V to 36V
• Up to 1A LED Current
• Adjustable 200kHz–2MHz Switching Frequency
• Adjustable Control of LED Current
• Integrated Boost Diode
• High Output Current Accuracy is Maintained Over a Wide Range from 35mA to 1A
• Open LED (LT3474) and Short-Circuit Protection
• High Side Sense Allows Grounded Cathode Connection
• Uses Small Inductors and Ceramic Capacitors
• LT3474-1 Drives LED Strings Up to 26V
• Compact 16-Lead TSSOP Thermally Enhanced Surface Mount Package

Typical Application

Description

The LT3474/LT3474-1 are fixed frequency step-down DC/DC converters designed to operate as constant-current sources. An internal sense resistor monitors the output current allowing accurate current regulation, ideal for driving high current LEDs. High output current accuracy is maintained over a wide current range, from 35mA to 1A, allowing a wide dimming range.

Unique PWM circuitry allows a dimming range of 400:1, avoiding the color shift normally associated with LED current dimming.

The high switching frequency offers several advantages, permitting the use of small inductors and ceramic capacitors. Small inductors combined with the 16 lead TSSOP surface mount package save space and cost versus alternative solutions. The constant switching frequency combined with low-impedance ceramic capacitors result in low, predictable output ripple.

With their wide input range of 4V to 36V, the LT3474/ LT3474-1 regulate a broad array of power sources, from 5V logic rails to unregulated wall transformers, lead acid batteries and distributed power supplies. A current mode PWM architecture provides fast transient response and cycle-by-cycle current limiting. Frequency foldback and thermal shutdown provide additional protection.