Microchip TCM809SVNB713 Voltage Monitor: Features and Application Circuit Design

In modern electronic systems, ensuring reliable operation and preventing unpredictable behavior during power-up, power-down, or brownout conditions is paramount. Voltage monitor circuits, also known as microprocessor supervisory circuits or reset ICs, are critical components dedicated to this task. The Microchip TCM809SVNB713 is a prominent example of such a device, offering a robust and compact solution for system monitoring and control.

Key Features of the TCM809SVNB713

The TCM809SVNB713 belongs to a family of 3-pin microcontroller reset circuits. Its primary function is to monitor the VDD supply voltage of a microcontroller (MCU) or digital system and assert a reset signal whenever the voltage falls below a predefined threshold. This ensures the MCU remains in a known safe state until the power supply stabilizes.

This specific variant is characterized by several key features:

Precise Voltage Monitoring: It is designed with a fixed voltage threshold of 3.08V (for the 3V version), making it ideal for monitoring 3.3V and 3V power supply rails. The high accuracy of the threshold voltage is crucial for predictable system behavior.

Active-Low Reset Output: The device provides an open-drain, active-low reset output (/RESET). This configuration offers design flexibility, as it can be easily pulled up to a voltage rail different from the monitored VDD, which is useful in mixed-voltage systems.

Manual Reset Capability: Although the standard TCM809 is a 3-pin device (VDD, GND, /RESET), many variants in this family, including those with a "VNB" suffix, integrate a fourth pin for a manual reset input. This allows a system operator to initiate a reset via an external switch, adding a layer of control for debugging or operational purposes.

Ultra-Low Supply Current: The device consumes very little power, typically only 5 µA, making it perfectly suited for battery-powered and portable applications where power efficiency is critical.

Small Form Factor: It is available in space-saving packages like SOT-23, which is essential for modern, compact PCB designs.

Application Circuit Design

Implementing the TCM809SVNB713 in a circuit is straightforward, thanks to its minimal external component requirement. A typical application circuit for monitoring a microcontroller's power supply is shown below.

 Figure 1: Typical application circuit for the TCM809SVNB713.

Circuit Operation:

1. Power Supply Connection: The VDD pin (Pin 1) is connected directly to the positive rail of the power supply being monitored (e.g., 3.3V). The GND pin (Pin 2) is connected to the system ground.

2. Reset Output: The /RESET output (Pin 3) is connected to the active-low reset input pin of the microcontroller. An external pull-up resistor (R1, typically 10kΩ to 100kΩ) is required to pull the signal high when the output transistor is off. This resistor pulls the /RESET line to the MCU's logic high voltage, which can be the same as or different from the monitored VDD.

3. Manual Reset Input (Optional): If the specific variant includes a manual reset (MR) pin, it can be connected to a tactile switch that ties to ground. When the switch is pressed, it pulls the MR pin low, forcing the /RESET output active regardless of the VDD voltage. A simple debounce circuit (a capacitor, C1) is often added in parallel to the switch to suppress contact bouncing.

4. Timing: The device features a fixed reset timeout period (typically 140 ms min). After VDD rises above the threshold voltage, the /RESET signal remains asserted for this timeout period to ensure the MCU and the power supply are fully stable before the system starts operation.

Design Considerations:

For optimal noise immunity, it is recommended to place a decoupling capacitor (0.1 µF to 1 µF) as close as possible to the VDD and GND pins of the TCM809.

The trace connecting the /RESET output to the MCU should be kept short to minimize noise coupling and signal integrity issues.

ICGOODFIND Summary

The Microchip TCM809SVNB713 is an exceptionally efficient and reliable voltage monitoring solution. Its integration of precise voltage monitoring, manual reset capability, and ultra-low power consumption into a tiny package makes it an indispensable component for enhancing the reliability of microcontroller-based systems, from consumer electronics to industrial controls. Its simple application circuit allows for quick implementation, ensuring systems operate only under valid power conditions.

Keywords: Voltage Monitor, Reset IC, Microcontroller Supervisory, Brownout Protection, Low-Power Design