Analog Devices Inc./Maxim Integrated DS1231S-35+

Overview

DS1231S-35+ from Maxim Integrated is a power monitor IC that detects impending power failure by monitoring both high-voltage input (IN) and +5V supply (VCC), provides dual reset outputs (RST active-high, RST active-low open-drain), and generates non-maskable interrupt (NMI) with programmable trip thresholds. It supports 5% or 10% VCC detection (TOL pin-selectable), operates from 4.5V to 5.5V, and delivers 150ms minimum power-up reset pulse.

For engineers reviewing the DS1231S-35+ datasheet, DS1231S-35+ pinout, DS1231S-35+ application, or DS1231S-35+ equivalent, key selection criteria include VCC trip accuracy (±5% or ±10%), IN pin mode flexibility (high-Z vs. 30µA current source), NMI-to-RST timing margin, dual-reset interface compatibility, and SOIC-16 surface-mount packaging for industrial embedded systems requiring orderly shutdown and automatic restart.

Technical Context

The DS1231S-35+ integrates two independent comparators: one monitors VCC against temperature-compensated reference (trip points 4.25V or 4.50V, selectable via TOL pin), while the other monitors IN pin voltage with hysteresis (VTP+ = 2.5V or VTP− = 2.15V depending on MODE pin state). Its digital sampler and delay logic ensure precise timing between NMI assertion and RST activation during power-down.

It features dual reset outputs: RST (push-pull, active-high) and RST (open-drain, active-low), both held active ≥150ms on power-up; NMI output responds within 200µs of IN threshold crossing. Input pin supports two configurations-high-impedance sensing (MODE=VCC) or 30µA current-source interface (MODE=GND)-enabling direct connection to AC-derived sense networks or UL-approved opto-isolators.

Key Specifications

Pinout & Package

DS1231S-35+ is housed in a 16-pin SOIC package (300-mil width), with 8 unused no-connect (NC) pins and dual RST outputs sharing functional roles across complementary logic states.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690TSA+ and TPS3808G33DBVR, DS1231S-35+ uniquely combines dual reset outputs, programmable VCC/NMI thresholds, and isolated high-voltage sensing-making it the only option for systems requiring coordinated shutdown, non-maskable alerting, and AC-line correlation.

Availability

DS1231S-35+ is available at Aetrix Electronics and suitable for industrial control systems, medical diagnostic equipment, telecom power shelves, and embedded computing platforms requiring stable component supply and long-term lifecycle support.

Supply support for DS1231S-35+ 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

Maxim Integrated (now part of Analog Devices) designs precision analog, mixed-signal, and power management ICs for industrial, automotive, and communications applications.

The DS1231S-35+ belongs to Maxim's legacy power monitoring product line, engineered specifically for systems demanding deterministic power-failure response, nonvolatile memory protection, and seamless integration with isolated AC sensing topologies.

FAQ

What is the function of the MODE pin on the DS1231S-35+?

The MODE pin on the DS1231S-35+ selects the electrical behavior of the IN pin: when tied to VCC, IN becomes a high-impedance input (VTP− = 2.15V) for resistor-divider sensing; when grounded, IN sources 30µA (VTP+ = 2.5V) for opto-isolator or switch-based interfaces. This dual-mode capability enables DS1231S-35+ to adapt to diverse power-loss detection architectures without external component changes.

How does the TOL pin affect the VCC trip point of the DS1231S-35+?

The TOL pin on the DS1231S-35+ sets the VCC undervoltage threshold: connecting TOL to GND selects a 4.50V trip point (5% below nominal 4.75V), while connecting TOL to VCC selects 4.25V (10% below). Both thresholds include ±120mV tolerance over temperature, and DS1231S-35+ guarantees RST/RST assertion within 100ns of VCC crossing the selected threshold.

Does the DS1231S-35+ require external pull-up resistors?

Yes-the RST output of the DS1231S-35+ is open-drain and requires an external pull-up resistor to VCC or another logic rail; RST is push-pull and does not require external components. The pull-up value is typically 4.7kΩ for standard TTL loads, and DS1231S-35+ specifies IOL ≥2.0mA at 0.4V to ensure robust low-state drive under worst-case conditions.

What is the guaranteed minimum power-up reset duration for the DS1231S-35+?

The DS1231S-35+ guarantees a minimum power-up reset duration of 150ms for both RST and RST outputs, measured from VCC reaching 4.5V until reset release. This specification holds across the full operating temperature range (0°C to +70°C) and ensures sufficient time for +5V supply stabilization and microprocessor clock lock before execution begins.

Can the DS1231S-35+ monitor both AC line voltage and VCC simultaneously?

Yes-the DS1231S-35+ simultaneously monitors VCC (pin 8) and high-voltage input (pin 1) using independent comparators. The IN pin supports AC-derived sensing via resistor divider (MODE=VCC) or opto-isolator (MODE=GND), while VCC monitoring uses an internal temperature-compensated reference. This dual-path architecture enables DS1231S-35+ to correlate upstream AC loss with downstream DC rail collapse for optimal shutdown timing.