36V, 2A Synchronous Buck-Boost Converter and LED Driver
The LT3942 from Analog Devices is a monolithic 4-switch synchronous buck-boost LED driver. The driver can regulate the LED string current up to 34V with input voltages above, below, or equal to the output voltage. The proprietary peak-buck peak-boost current mode control scheme allows adjustable and synchronizable 300kHz to 2MHz fixed frequency operation, or internal 25% triangle spread spectrum operation for low EMI.
With 3V to 36V input, 0V to 36V output and seamless low-noise transitions between operation regions, the LT3942 is designed for LED driver applications in automotive, industrial and battery-powered systems. The schematic above illustrates a typical application with the LT3942 used in a 93% efficient, 12W (12V, 1A) 2MHz buck-boost LED driver circuit.
The LT3942 provides LED current regulation with up to 128:1 internal and 5000:1 external pwm dimming using an optional high-side PMOS switch. The CTRL pin provides flexible 20:1 analog dimming with ±2.5% LED current regulation at 100mV full scale. Robust fault protection detects an open or short LED condition, during which the LT3942 retries, latches off, or keeps running.
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Summary of Features and Specifications
- 4-Switch Single Inductor Architecture Allows VIN Above, Below or Equal to VOUT
- Proprietary Peak-Buck Peak-Boost Current Mode
- 3V to 36V Input Voltage Range
- 0V to 36V Output Voltage Range
- ±1.5% Output Voltage Regulation
- ±3% LED Current Regulation
- 5000:1 External and 128:1 Internal PWM Dimming
- Rail-to-Rail LED Current Sense and Monitor Output
- Open and Short LED Protection with Fault Reporting
- 300kHz to 2MHz Fixed Switching Frequency with External Frequency Synchronization
- Flicker-Free Spread Spectrum for Low EMI
- Available in 28-Lead QFN (4mm × 5mm)
