Microchip MCP121T-300E/TT 0V Voltage Supervisor: Datasheet and Application Circuit Design Guide

The Microchip MCP121T-300E/TT is a precision voltage supervisory circuit designed to monitor a system's power supply voltage and provide a reset signal to a microcontroller or microprocessor upon power-up, power-down, or brown-out conditions. This device is critical for ensuring system stability and preventing erratic operation in embedded systems, consumer electronics, and industrial applications.

Key Features from the Datasheet

The MCP121T-300E/TT belongs to a family of voltage supervisors with a fixed threshold voltage of 3.00V. Its primary function is to assert a reset signal whenever the monitored VDD supply drops below this preset threshold. The device features an open-drain output, providing design flexibility as it requires an external pull-up resistor to the desired logic voltage. Key electrical characteristics include an extremely low supply current of typically 5.5 µA, making it ideal for battery-powered and low-power applications. It is available in a space-saving SOT-23-3 package, suitable for compact PCB designs.

Application Circuit Design Guide

A typical application circuit for the MCP121T-300E/TT is straightforward yet highly effective. The core design involves only a few external components.

1. Basic Connection: The VDD pin is connected directly to the power supply rail being monitored (e.g., the microcontroller's VCC). The GND pin is connected to the system ground.

2. Open-Drain Output (/RST): The reset output pin is an open-drain active-low signal. It must be connected to the microcontroller's reset pin through a pull-up resistor (typically 10 kΩ). This resistor pulls the line high when the output is not asserted. The pull-up voltage can be connected to the microcontroller's VCC or another voltage rail within the output's voltage limits, offering flexibility for mixed-voltage systems.

3. Bypass Capacitor: For enhanced noise immunity and stability, it is recommended to place a 0.1 µF ceramic bypass capacitor between the VDD pin and ground, as close to the device as possible.

When the supply voltage (VDD) rises above the 3.00V threshold, the reset signal is de-asserted (pulled high) after a fixed delay time, allowing the power supply and system clock to stabilize before the microcontroller begins operation. Conversely, if VDD falls below the threshold, the reset signal is immediately asserted (pulled low), placing the microcontroller into a known safe state.

ICGOOODFIND: The Microchip MCP121T-300E/TT is an extremely reliable and simple solution for system voltage monitoring. Its ultra-low quiescent current, precise voltage threshold, and minimal external component requirement make it a superior choice for designers aiming to enhance system reliability and safety without compromising power budget or board space.

Keywords: Voltage Supervisor, Microcontroller Reset, Brown-Out Detection, Open-Drain Output, Low-Power Design.