Analog Devices Inc./Maxim Integrated DS1231-35N

Overview

DS1231-35N from Maxim Integrated (now Analog Devices) is a precision power monitor IC designed to detect impending power failure and initiate orderly processor shutdown. It features dual-voltage monitoring (VCC and high-voltage input), selectable 5% or 10% VCC trip thresholds (4.75 V or 4.50 V nominal), NMI and dual RST outputs (active-high and open-drain), and operates across 4.5–5.5 V supply with 0.5–2.0 mA quiescent current. It is used in industrial control systems requiring nonvolatile memory protection during AC line transients.

For engineers reviewing the DS1231-35N datasheet, DS1231-35N pinout, DS1231-35N application, or DS1231-35N equivalent, key selection considerations include its dual comparator architecture (IN and VCC), MODE-selectable input impedance (high-Z or 30 µA current source), TOL-configurable VCC threshold accuracy, and compatibility with both linear and switching power supplies without external capacitors.

Technical Context

The DS1231-35N integrates two independent comparators: one monitors VCC against a temperature-compensated reference to generate RST/RST signals at programmable thresholds (4.75 V or 4.50 V), while the second monitors the high-voltage IN pin with MODE-selectable input characteristics-either high-impedance (2.3 V trip, Mode=VCC) or 30 µA current sourcing (2.5 V trip, Mode=GND). Hysteresis of ±60 mV ensures noise immunity on both inputs.

Its digital sampler and delay logic coordinate timing between NMI assertion and RST activation, ensuring maximum usable hold-up time before forced reset. On power-up, RST/RST remain active for ≥150 ms to guarantee stable supply conditions, and NMI releases only after both VCC stabilization and IN threshold crossing-enabling precise early-warning sequencing in microprocessor-based systems.

Key Specifications

Pinout & Package

DS1231-35N is supplied in an 8-pin DIP package (300 mil width), with pin 1 designated as IN, pin 2 as MODE, pin 3 as TOL, pin 4 as GND, pin 5 as RST (active-high), pin 6 as RST (open-drain), pin 7 as NMI, and pin 8 as VCC. All NC pins are internally unconnected and must remain floating.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar power monitoring applications.

Compared with MAX690CPA+ and TPS3823-50DBVR, DS1231-35N uniquely provides simultaneous high-voltage and regulated-rail monitoring with configurable thresholds and dedicated NMI signaling-making it irreplaceable in applications requiring deterministic, multi-stage power-failure response with minimal external components.

Availability

DS1231-35N is available at Aetrix Electronics and suitable for industrial automation, medical diagnostics, telecom infrastructure, and point-of-sale terminals requiring stable component supply and long-term obsolescence management.

Supply support for DS1231-35N 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 (via acquisition of Maxim Integrated) designs precision analog, mixed-signal, and power management ICs for high-reliability industrial, automotive, and communications systems.

The DS1231-35N belongs to Maxim's legacy Power Monitor family, engineered specifically for microprocessor-based systems needing fail-safe power supervision with early warning, automatic restart, and nonvolatile memory protection under transient AC conditions.

FAQ

What is the function of the MODE pin on the DS1231-35N?

The MODE pin on the DS1231-35N selects the electrical behavior of the IN pin: when tied to VCC, IN becomes a high-impedance input (2.3 V trip point) for use with resistor dividers; when grounded, IN acts as a 30 µA current source (2.5 V trip point) for direct opto-isolator interfacing. This dual-mode capability allows DS1231-35N to adapt to either isolated or non-isolated power-loss detection topologies without redesign.

How does the DS1231-35N ensure reliable reset assertion during power-up?

The DS1231-35N guarantees reset assertion for ≥150 ms after VCC reaches valid levels, per its internal power-on reset circuitry. This timing is independent of external components and ensures the microprocessor receives a clean, extended reset pulse-allowing full stabilization of clocks, PLLs, and peripheral power rails before firmware execution begins. DS1231-35N maintains this behavior across its full operating temperature range.

Can the DS1231-35N monitor both AC line voltage and +5 V DC simultaneously?

Yes-the DS1231-35N monitors two independent voltage domains: the IN pin accepts a scaled version of AC line voltage (e.g., via rectifier and resistor divider), while the VCC pin continuously supervises the +5 V regulated supply. Its dual-comparator architecture enables DS1231-35N to issue an NMI at the first sign of AC sag and follow with RST only when the local DC rail collapses-providing layered, time-staged power-failure response.

What is the purpose of the TOL pin on the DS1231-35N?

The TOL pin on the DS1231-35N configures the VCC detection threshold: grounding TOL sets a 4.75 V trip point (±5% of 5 V), while connecting it to VCC selects a 4.50 V threshold (±10%). This allows DS1231-35N to match system-level brownout tolerance requirements without changing external components-supporting both tight-margin and robust industrial designs using the same footprint.

Does the DS1231-35N require external pull-up resistors?

Only the RST (pin 6) output requires an external pull-up resistor, as it is an open-drain driver; the RST (pin 5) output is push-pull and drives high/low actively. The NMI output is also push-pull and needs no external resistor. DS1231-35N's internal design eliminates all other external passive components-including timing capacitors-reducing bill-of-materials and improving reliability.