**ADM8660ANZ: A Comprehensive Technical Overview and Application Note**

The **ADM8660ANZ** is a highly integrated, micropower supervisory circuit from Analog Devices, designed to monitor power supply voltages in digital systems. It provides a critical function: ensuring a microprocessor or microcontroller operates reliably by monitoring its power source and executing a controlled reset sequence during power-up, power-down, or brownout conditions. This article delves into the technical specifications, key features, and practical application circuits for this essential component.

**Core Functionality and Key Features**

At its heart, the ADM8660ANZ is a **voltage supervisor and watchdog timer**. Its primary role is to assert a reset signal to the host microprocessor whenever the supply voltage (VCC) drops below a predefined threshold. This prevents the CPU from operating with insufficient voltage, which can lead to erratic code execution and system failure.

The device integrates several vital functions into a single 8-pin package:

* **Precision Voltage Monitoring:** The ADM8660ANZ is available in factory-programmed threshold voltages (e.g., 4.65V, 3.08V, 2.93V) with tight tolerances, ensuring accurate monitoring for 5V, 3.3V, and 3V systems.

* **Manual Reset Input:** A active-low MR input allows a external switch or logic signal to initiate a reset on demand, providing added control for the system designer.

* **Watchdog Timer:** This feature monitors the microprocessor’s activity. If the CPU fails to toggle the ADM8660’s WDI input within a preset timeout period (typically 1.6 seconds), the watchdog timer expires, and the device asserts a reset. This safeguards the system from software crashes or lockups.

* **Power-Fail Comparator:** An additional, uncommitted comparator is provided for early warning of an impending power failure. This allows the microprocessor to perform an orderly shutdown, such as saving critical data to non-volatile memory, before the main reset is asserted.

* **Micropower Operation:** With extremely low supply current, the ADM8660ANZ is ideal for **battery-powered and portable applications** where power conservation is paramount.

**Internal Architecture and Pin Configuration**

The ADM8660ANZ combines three main blocks: the reset generator, the watchdog timer, and the power-fail comparator. Key pins include:

* **VCC:** Supply voltage input.

* **GND:** Ground.

* **RESET / RESET:** Active-low and active-high reset outputs.

* **WDI:** Watchdog timer input.

* **MR:** Manual reset input (active-low).

* **PFI:** Power-fail comparator input.

* **PFO:** Power-fail comparator output (active-low).

**Application Circuits and Design Considerations**

A typical application circuit for microprocessor monitoring is straightforward. The VCC pin is connected to the system's power rail. The RESET output is connected directly to the reset pin of the microprocessor. A capacitor on the MR pin can provide power-on reset delay, and a simple switch can be added for a manual reset function.

To implement the watchdog feature, a GPIO line from the microprocessor must be programmed to periodically toggle the WDI pin. If this toggling stops, the ADM8660ANZ resets the CPU.

The power-fail comparator is highly useful for monitoring an intermediate voltage point in a power supply, often before a regulator. By using a resistor divider from a higher-voltage rail (e.g., an unregulated DC input) to the PFI pin, the PFO output can go low *before* the main VCC rail begins to decay, providing valuable lead time for the CPU.

**Design Best Practices:**

1. **Decoupling:** Place a 0.1µF ceramic capacitor close to the VCC pin to ensure stable operation.

2. **Watchdog Management:** Ensure the software toggles WDI within the timeout window, but not too frequently, to avoid accidentally resetting the system.

3. **Threshold Selection:** Carefully select the device variant with a voltage threshold appropriate for your microprocessor's minimum operating voltage.

**ICGOODFIND**

The ADM8660ANZ stands as a robust and highly reliable solution for system supervision. Its integration of multiple critical functions—**precision voltage monitoring, a watchdog timer, and a power-fail comparator**—into a single chip simplifies design, reduces board space, and significantly enhances the reliability of microprocessor-based systems across a wide range of industrial, medical, and consumer applications.

**Keywords:** Power Supply Monitor, Voltage Supervisor, Watchdog Timer, Microprocessor Reset, Brownout Detection.