Analog Devices Inc. ADM708ARZ

Overview

ADM708ARZ from Analog Devices is a low-cost microprocessor supervisory circuit with 4.40 V reset threshold, 200 ms reset pulse width, 190 μA quiescent current, active-high RESET output, and power-fail comparator (PFI/PFO) for 5 V systems. It monitors supply voltage during power-up, brownout, and power-down conditions in embedded controllers and intelligent instruments.

For engineers reviewing the ADM708ARZ datasheet, ADM708ARZ pinout, ADM708ARZ application, or ADM708ARZ equivalent, key selection criteria include guaranteed RESET validity down to VCC = 1 V, TTL/CMOS-compatible manual reset input (MR), absence of watchdog timer, and SOIC-8 packaging for industrial temperature range (−40°C to +85°C).

Technical Context

The ADM708ARZ implements a precision voltage monitor with fixed 4.40 V threshold and 40 mV hysteresis, ensuring reliable reset assertion during 5 V supply droop. Its internal 1.25 V reference enables independent power-fail detection via external resistive divider on PFI.

It provides dual reset outputs: active-low RESET and active-high RESET - both asserted for 200 ms after VCC rises above threshold or MR deasserts. The MR input features internal 250 μA pull-up and 150 ns minimum pulse width tolerance, supporting switch or logic-driven reset initiation.

Key Specifications

Pinout & Package

ADM708ARZ is packaged in an 8-lead SOIC_N (R-8) package per JEDEC MS-012-AA, with 1.27 mm lead pitch, 4.90 mm × 3.90 mm body, and gull-wing leads. Pin 1 is marked by a beveled corner or notch.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar microprocessor supervisory applications.

Compared with MAX708CSA+, ADM708ARZ adds integrated PFI/PFO for auxiliary supply monitoring without external components; compared with TPS3808G33DBVR, ADM708ARZ supports 5 V systems, offers dual-reset polarity, and delivers higher accuracy reset threshold (±0.15 V vs. ±2.5%) at the cost of higher quiescent current.

Availability

ADM708ARZ is available at Aetrix Electronics and suitable for industrial PLC controllers, embedded data loggers, medical infusion pumps, and point-of-sale terminals requiring stable component supply across extended product lifecycles.

Supply support for ADM708ARZ includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices is a global semiconductor company specializing in high-performance analog, mixed-signal, and digital signal processing technologies for precision measurement and control.

The ADM705–ADM708 family was designed specifically for robust, low-cost microprocessor supervision in 5 V systems, emphasizing guaranteed reset operation down to 1 V and integrated power-fail warning capability.

FAQ

What is the reset threshold voltage of the ADM708ARZ and how is it used in system design?

The ADM708ARZ has a fixed reset threshold of 4.40 V ±0.15 V. This value determines the supply voltage level below which the device asserts RESET to prevent microprocessor operation during brownout conditions. In system design, it ensures the host processor remains held in reset until the 5 V rail stabilizes above this threshold and sustains it for 200 ms, allowing sufficient time for oscillator startup and internal register initialization. The 40 mV hysteresis prevents oscillation near the trip point under noisy or slowly varying supply conditions.

Does the ADM708ARZ include a watchdog timer function?

No, the ADM708ARZ does not include a watchdog timer. It belongs to the ADM707/ADM708 variant group, which omits the WDI and WDO pins present in ADM705/ADM706. Instead, ADM708ARZ provides dual-reset outputs (active-low and active-high RESET) and a dedicated power-fail comparator (PFI/PFO). If watchdog functionality is required, the ADM706ARZ - which shares the same 4.40 V threshold and SOIC-8 package - should be selected.

How is the PFI input used in the ADM708ARZ, and what external components are needed?

The PFI input on the ADM708ARZ connects to the noninverting input of an internal 1.25 V comparator. To monitor a secondary supply (e.g., 3.3 V or battery), a resistive divider scales that voltage so it crosses 1.25 V at the desired trip point. For example, monitoring a 3.6 V Li-ion cell for 3.0 V cutoff requires R1 = 180 kΩ and R2 = 100 kΩ. No external reference or op-amp is needed. If unused, PFI must be tied to GND to avoid floating input noise.

What is the purpose of the NC pin on the ADM708ARZ, and how should it be handled on the PCB?

Pin 6 on the ADM708ARZ is designated NC (No Connect) and is internally unconnected. It must remain electrically floating - neither tied to VCC nor GND - to avoid unintended coupling or leakage paths. On the PCB, this pin may be left unlanded or fitted with a non-plated via; routing traces to or from it is prohibited. This differs from ADM705/ADM706, where pin 6 is WDI, confirming that ADM708ARZ's functional set excludes watchdog capability.

Can the ADM708ARZ operate with supply voltages below 5 V, and what is its minimum functional VCC?

Yes, the ADM708ARZ operates over VCC = 1.0 V to 5.5 V. Its key specification is guaranteed RESET output validity down to VCC = 1 V - meaning the RESET pin maintains a defined logic state (low for RESET, high for RESET) even as the supply collapses. This ensures deterministic microprocessor hold-down during deep brownouts or battery discharge, unlike many supervisors that cease functioning below ~2.5 V. At VCC = 1 V, RESET sinks 50 µA while maintaining ≤0.3 V, satisfying most 1.8 V logic input thresholds.