Microchip MCP809T-475I/TT 3-Pin Microprocessor Reset Circuit Technical Overview

In the realm of embedded systems and electronic design, ensuring a microcontroller or microprocessor starts up correctly and recovers predictably from power disruptions is paramount. The Microchip MCP809T-475I/TT is a dedicated 3-pin microprocessor supervisory circuit, specifically engineered to provide a simple yet highly reliable solution for this critical function. This device monitors the system's power supply voltage and asserts a reset signal to the processor whenever an out-of-tolerance condition is detected, thereby preventing erratic code execution and system failure.

The core functionality of the MCP809T revolves around its precise 4.75V reset threshold voltage. This specific voltage is a common requirement for many systems operating from a nominal 5V supply rail. When the VDD supply voltage drops below this 4.75V threshold—whether during power-down, power-up, or a brownout event—the device immediately asserts an active-low reset signal (/MR). This signal remains asserted until VDD rises above the threshold voltage and remains stable for a minimum of 140 milliseconds (typ), a delay period engineered to ensure the power supply and processor oscillator have stabilized. This built-in timeout period is crucial for system integrity, eliminating the need for external timing components and simplifying design.

Housed in a space-saving SOT-23-3 package, the MCP809T-475I/TT is designed for applications where board real estate is at a premium. Its three-pin interface (VDD, GND, and /MR) makes implementation exceptionally straightforward. The active-low open-drain output on the /MR pin provides design flexibility, allowing it to be easily pulled up to a voltage rail different from the monitored VDD, which is useful in mixed-voltage systems. Furthermore, the device features exceptionally low supply current, typically drawing just 7.5 µA, making it an ideal choice for battery-powered and other power-sensitive applications.

Robust performance is guaranteed across an industrial temperature range from -40°C to +85°C, ensuring reliability in harsh environmental conditions. The MCP809T is also highly immune to brief voltage transients, reducing the likelihood of false reset signals which can disrupt system operation.

ICGOOODFIND: The Microchip MCP809T-475I/TT is an exemplary solution for microprocessor reset management, offering a robust, compact, and ultra-low-power design. Its precise voltage monitoring, integrated delay timer, and simple 3-pin configuration make it an indispensable component for enhancing the reliability and stability of a vast array of electronic systems, from consumer gadgets to industrial controls.

Keywords: Microprocessor Supervisor, Reset Circuit, Voltage Monitoring, Brownout Protection, Low-Power.