Analog Devices Inc./Maxim Integrated DS1231-35N+

Overview

DS1231-35N+ 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), generates non-maskable interrupt (NMI), and supports 5% or 10% VCC threshold detection via TOL pin - used in industrial control systems requiring orderly shutdown before brownout.

For engineers reviewing the DS1231-35N+ datasheet, DS1231-35N+ pinout, DS1231-35N+ application, or DS1231-35N+ equivalent, key selection criteria include VCC trip accuracy (±5% or ±10%), IN pin hysteresis (60 mV), dual-reset signaling, NMI timing delay (≤200 µs), and compatibility with linear/switching supplies without external capacitors.

Technical Context

The DS1231-35N+ integrates two independent comparators: one monitors VCC against selectable 4.25 V (TOL=VCC) or 4.75 V (TOL=GND) thresholds with 150–1000 ms power-up reset hold time; the other monitors IN pin voltage with mode-selectable input characteristics - high-impedance (Mode=VCC, VTP−=2.15 V) or 30 µA current-source (Mode=GND, VTP+=2.5 V).

It features temperature-compensated reference circuitry, built-in hysteresis (60 mV), noise-immune input sensing, and automatic restart after power restoration. The device operates across 0°C to 70°C, draws 0.5–2.0 mA ICC, and requires no external timing capacitors - enabling direct interface to microprocessors, opto-isolators, or AC-derived sense networks.

Key Specifications

Pinout & Package

DS1231-35N+ is supplied in an 8-pin DIP package (300 mil width), with pins arranged as follows:

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690EPA+ and TPS3823-50DBVR, DS1231-35N+ uniquely delivers simultaneous NMI alert and dual-mode reset signaling with no external components - making it essential for systems requiring deterministic shutdown sequencing and AC-line-level fault anticipation.

Availability

DS1231-35N+ is available at Aetrix Electronics and suitable for industrial PLCs, medical monitoring devices, telecom shelf controllers, and point-of-sale terminals requiring stable component supply and long-term lifecycle support.

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

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

The DS1231-35N+ belongs to Maxim's legacy power supervision product line, engineered specifically for reliable, capacitor-free power-failure detection and orderly microprocessor shutdown in commercial-grade embedded systems.

FAQ

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

The MODE pin on the DS1231-35N+ configures the IN pin's electrical behavior: when tied to VCC, IN becomes a high-impedance input (VTP− = 2.15 V) for resistor-divider AC sensing; when grounded, IN sources 30 µA (VTP+ = 2.5 V) to drive opto-isolator LEDs. This dual-mode capability allows DS1231-35N+ to interface safely with either high-voltage AC lines or isolated DC rails without external biasing components.

How does the TOL pin affect the DS1231-35N+ reset threshold?

The TOL pin on the DS1231-35N+ selects the VCC undervoltage detection threshold: connecting TOL to GND sets a 4.75 V trip point (5% below nominal 5 V), while connecting TOL to VCC sets a 4.25 V trip point (10% below). This allows DS1231-35N+ to match system-specific brownout margins - ensuring RST assertion occurs before critical logic fails but after sufficient hold-up time remains for safe shutdown.

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

Yes, the DS1231-35N+ requires an external pull-up resistor on the RST (pin 6) output, which is an open-drain driver. The RST (pin 5) output is push-pull and does not require a pull-up. Typical pull-up values range from 4.7 kΩ to 10 kΩ to +5 V, selected to ensure adequate sink current (≥2.0 mA) while limiting power consumption - a design requirement explicitly stated in the DS1231-35N+ datasheet timing diagrams and electrical characteristics.

What is the maximum input voltage allowed on the IN pin of the DS1231-35N+?

The DS1231-35N+ specifies a maximum allowable voltage of 5.0 V on the IN pin (pin 1), regardless of MODE configuration. Exceeding this violates absolute maximum ratings and risks latch-up or permanent damage. When interfacing to higher-voltage sources (e.g., rectified AC), a resistor divider must scale the sense voltage to ≤5.0 V - with the divider ratio constrained by the IN trip point (2.15 V or 2.5 V) and 60 mV hysteresis, as defined in the DS1231-35N+ application circuits.

Can the DS1231-35N+ be used in automotive applications?

No, the DS1231-35N+ is rated for 0°C to 70°C operation and lacks AEC-Q100 qualification, automotive-grade packaging, or extended temperature support. Its specification sheet explicitly lists only commercial-grade temperature range and does not include automotive stress testing, ESD robustness beyond 2 kV HBM, or vibration/shock compliance. For automotive use, DS1231-35N+ must be replaced with qualified alternatives such as the MAX6369 or TLV809 - DS1231-35N+ is intended solely for commercial and industrial embedded systems.