Features

• ±2% LED Current Regulation
• ±2% Output Voltage Regulation
• 5000:1 PWM Dimming at 100Hz
• 128:1 Internal PWM Dimming
• Spread-Spectrum Frequency Modulation
• Silent Switcher^® Architecture for Low EMI
• Operates in Boost, Buck Mode and Buck-Boost Mode
• 2.8V to 36V Input Voltage Range
• Up to 34V LED String Voltage
• 2A, 40V Internal Switches
• 200kHz to 2MHz with SYNC Function
• Analog or Duty Cycle LED Current Control
• Open/Short LED Protection and Fault Indication
• Thermally Enhanced 28-Pin (4mm × 5mm) QFN

Typical Application

Description

The LT®3922 is a monolithic, synchronous, step-up DC/ DC converter that utilizes fixed-frequency, peak current control and provides PWM dimming for a string of LEDs. The LED current is programmed by an analog voltage or the duty cycle of pulses at the CTRL pin. The LT3922 will maintain ±2% current regulation through an external sense resistor over a wide range of output voltages.

The switching frequency is programmable from 200kHz to 2MHz by an external resistor at the RT pin or by an external clock applied at the SYNC/SPRD pin. With the optional spread spectrum frequency modulation enabled, the frequency varies from 100% to 125% to reduce EMI. The LT3922 also includes a driver for an external high side PMOS for PWM dimming and an internal PWM signal generator for analog control of PWM dimming when an external signal is not available.

Additional features include an accurate external reference voltage for use with the CTRL and PWM pins, an LED current monitor, an accurate EN/UVLO pin threshold, open-drain fault reporting for open-circuit and short-circuit load conditions, and thermal shutdown.