The range of applications for LEDs has expanded significantly, moving beyond general lighting to include automotive, industrial, test equipment, signage, and safety systems. As a result, the demand for advanced LED drivers has grown. Modern LED solutions require compact, high-efficiency, low-noise drivers with excellent dimming capabilities and robust fault protection. The LT3922 is designed to meet these evolving needs effortlessly.
The LT3922 is a 36V, synchronous LED driver featuring an integrated 2A switch that can be configured as a boost, buck, or boost-buck topology. It is housed in a compact 4mm x 5mm QFN package and utilizes Analog Devices' advanced switching technology. This ensures a small footprint while maintaining high efficiency and controlled switching edges, which help reduce electromagnetic interference (EMI). The device's synchronized switches are optimized to minimize ringing, offering a balanced performance between efficiency and noise reduction. These switches can operate at frequencies up to 2.5MHz, making the solution ideal for space-constrained designs.
One of the key advantages of the LT3922 is its flexibility in topologies. It supports boost, buck, and boost-buck configurations, allowing designers to tailor the driver to specific application requirements. Regardless of the chosen topology, all features remain active, including internal PWM dimming, SSFM (spread spectrum frequency modulation), low EMI, ISMON output current monitoring, and comprehensive fault protection. This versatility makes it suitable for a wide range of applications, from automotive lighting to industrial machine vision systems.
In boost mode, the LT3922 can drive LED strings up to 34V with some headroom below 40V to prevent overvoltage issues. At 2MHz, it delivers 330mA with a 2000:1 PWM dimming ratio. The device is also capable of handling LED open and short-circuit conditions, reporting faults via the FAULT pin. Its high-frequency operation places fundamental EMI harmonics above the AM band, contributing to a cleaner signal. Additionally, SSFM can extend the switching frequency to 2.5MHz, further reducing EMI across multiple harmonics.
In buck mode, the LT3922 can handle input voltages up to 36V and drive LED strings with currents up to 1.5A. With a 400kHz operating frequency, it achieves up to 94% efficiency at 12V input and 89% at 36V. The design supports a 1000:1 PWM dimming ratio at 100Hz, making it ideal for applications requiring precise brightness control.
The boost-buck configuration allows the LT3922 to support input voltages both above and below the LED string voltage. This topology is particularly useful in applications where the input voltage fluctuates, such as in automotive systems. The device maintains low output ripple and passes rigorous EMI tests like CISPR 25 Class 5, ensuring compliance with stringent standards.
In automotive applications, the LT3922 excels due to its low EMI, high efficiency, and robust fault protection. It operates within a 9V to 16V input range and can withstand 36V transients and cold start conditions as low as 3V. Its Silent Switcher architecture, combined with SSFM and controlled switching edges, ensures minimal EMI, making it ideal for use in taillights, daytime running lights, and headlamps.
For machine vision systems, the LT3922 provides consistent LED output regardless of the flash interval. It digitally samples the converter state on the falling edge of the PWM signal, enabling long off-times without voltage droop. This feature is crucial in applications requiring precise timing, such as automated inspection systems, where the LED must maintain stable illumination even after extended periods of inactivity.
Internally generated PWM dimming simplifies design by eliminating the need for external clock sources. The LT3922 offers a 128:1 dimming ratio and can be configured for higher ratios using external signals. Combined with analog dimming, this allows for a total dimming range of up to 50,000:1, providing exceptional brightness control.
Overall, the LT3922 is a highly versatile and efficient LED driver that meets the demands of modern applications. Its compact size, high performance, and built-in protection make it an ideal choice for automotive, industrial, and machine vision systems. Whether used in a boost, buck, or boost-buck configuration, the LT3922 delivers reliable, low-noise operation with minimal EMI.
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