Analog Devices AN-139 Application Note Low-Voltage Power Supply Watch-Dog Monitor Circuit

About this manual

The document presents a simple circuit consisting of a reference diode and a matched PNP transistor pair (MAT-03) designed to monitor low voltage power rails, such as +5V logic supplies. This circuit is intended for use in microprocessor-based systems utilizing battery-backed-up CMOS or EEPROM memory.

What's inside

• A Low-Voltage Power Supply Watch-Dog Monitor Circuit
• Circuit Description and Operation
• Trip-Point Voltage Calculation
• Response Time Characteristics
• Hysteresis Implementation
• Active LOW Output Modification
• MAT-01 Transistor Pair Application

Specifications

Frequently asked questions

What components are used in the basic monitor circuit?

The circuit consists of a reference diode and a matched PNP transistor pair, specifically the MAT-03.

What is the purpose of this monitor circuit?

It prevents inadvertent writing to memory as the rest of the digital circuitry turns off with a falling +5V supply.