Overview
The LT1117CST-2.85#PBF is a member of the LT1117 family of low dropout voltage regulators, manufactured by Analog Devices. This IC is designed to provide a stable 2.85V output from a higher input voltage, with a typical dropout voltage of just 1.2V at 800mA load current. The device is packaged in a surface-mount SOT-223 form factor, making it suitable for compact PCB designs. The LT1117 series is particularly valued for its robust performance across a wide temperature range (-40°C to +125°C), making it suitable for industrial and automotive applications. It incorporates thermal shutdown and current limit protection features, enhancing its reliability in demanding environments.
Structure and Working Principle
The LT1117CST-2.85#PBF consists of a reference voltage source, error amplifier, pass transistor, and protection circuitry. The reference voltage remains stable against variations in input voltage and temperature. The error amplifier compares the output voltage (through a feedback network) with this reference and adjusts the pass transistor to maintain the desired output. When the input voltage exceeds the output voltage by at least the dropout voltage (1.2V typical), the regulator maintains the specified 2.85V output. The device automatically reduces output current if either excessive temperature or current is detected, protecting both the regulator and downstream components.
Key Features
The LT1117CST-2.85#PBF offers several notable features that make it popular in power management applications. Its low dropout voltage enables efficient operation even when the input voltage is only slightly higher than the output. The fixed 2.85V output eliminates the need for external resistors, simplifying circuit design. Additional features include 1% output voltage accuracy, thermal shutdown protection, and current limiting. The device has a low quiescent current (typically 5mA), which helps conserve power in battery-operated systems. The SOT-223 package provides good thermal characteristics while maintaining a small footprint on the PCB.
Application Areas
This voltage regulator finds extensive use in various electronic systems requiring stable 2.85V power rails. Common applications include power supplies for microcontrollers, FPGAs, and other digital ICs in industrial control systems. The automotive industry utilizes it for infotainment systems and engine control units where reliable voltage regulation is critical. Consumer electronics such as set-top boxes, routers, and IoT devices frequently incorporate the LT1117CST-2.85#PBF. Its robust design makes it suitable for medical equipment and test instruments where consistent performance is essential. The regulator is often used as a secondary voltage source after a switching regulator to provide clean power to sensitive analog circuits.
Maintenance and Precautions
Proper implementation of the LT1117CST-2.85#PBF requires attention to several design considerations. Adequate heat sinking should be provided when operating near maximum current ratings, as excessive heat can trigger thermal shutdown. Input capacitors (typically 10μF tantalum or aluminum electrolytic) are recommended to improve transient response and stability. Designers should ensure the input voltage never exceeds the absolute maximum rating (20V) and remains above the dropout voltage for proper regulation. Output capacitors (minimum 10μF) help maintain stability, especially with low ESR types. When laying out the PCB, place the regulator close to the load and use wide traces for current-carrying paths to minimize voltage drops.
B2B Procurement Guide
When procuring LT1117CST-2.85#PBF regulators in bulk, buyers should verify the manufacturer's part number and packaging (tape and reel for automated assembly). Consider purchasing from authorized distributors like Digi-Key, Mouser, or Arrow to ensure genuine components. Lead times for this popular part typically range from 2-8 weeks, so plan procurement accordingly. For high-volume purchases (10,000+ units), buyers may negotiate prices below $0.50 per unit. Request samples for testing before large orders, particularly when switching suppliers. Check for alternative parts in the LT1117 family if flexibility in output voltage is required. Many distributors offer value-added services like programming or kitting for complex BOMs.
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