Analog Devices Inc./Maxim Integrated DS1231S-35+T&R

Overview

DS1231S-35+T&R from Maxim Integrated (now Analog Devices) is a precision power monitor IC designed to detect impending power failure and initiate orderly microprocessor shutdown. It provides dual reset outputs (RST active-high, RST active-low open-drain), NMI interrupt, 5% or 10% VCC threshold detection (4.25V or 4.75V nominal), and configurable high-impedance or current-source input sensing - deployed in industrial control systems with linear or switching power supplies.

For engineers reviewing the DS1231S-35+T&R datasheet, DS1231S-35+T&R pinout, DS1231S-35+T&R application, or DS1231S-35+T&R equivalent, key selection criteria include VCC trip point accuracy (±2%, typ.), input hysteresis (+60 mV), NMI-to-RST timing margin (≥200 µs), and compatibility with UL-approved opto-isolators for AC line monitoring.

Technical Context

The DS1231S-35+T&R integrates two independent comparators: one monitors VCC against a temperature-compensated reference to generate RST/RST at selectable 4.25V (TOL=VCC) or 4.75V (TOL=GND) thresholds; the other monitors the IN pin with mode-selectable input characteristics - high-impedance (MODE=VCC, VTP−=2.15V) or 30 µA current source (MODE=GND, VTP+=2.5V).

It delivers deterministic power-up reset hold time (150–1000 ms), sub-microsecond NMI propagation delay (1.1 µs), and noise-immune hysteresis on both inputs. The device operates across 4.5–5.5V supply and supports 0°C to 70°C ambient, with no external capacitors required for basic functionality.

Key Specifications

Pinout & Package

DS1231S-35+T&R is supplied in a 16-pin SOIC (300 mil) surface-mount package, RoHS-compliant and tape-and-reel packaged (T&R). Pin 1 is MODE; Pin 16 is GND. 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 monitor applications.

Compared with DS1231S-35+T&R, MAX690TSA+ simplifies design where only VCC monitoring is required, while TPS3808G33DBVR offers threshold flexibility at the cost of added external components and loss of dedicated NMI signaling - making DS1231S-35+T&R optimal for systems requiring deterministic, multi-stage power-failure response.

Availability

DS1231S-35+T&R is available at Aetrix Electronics and suitable for industrial automation, medical diagnostics, telecom infrastructure, and test equipment requiring stable component supply and long-term obsolescence management.

Supply support for DS1231S-35+T&R 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 (acquired Maxim Integrated in 2021) designs high-performance analog, mixed-signal, and power management ICs for precision sensing, signal conditioning, and system reliability.

The DS1231S-35+T&R belongs to Maxim's legacy Power Monitoring family, engineered specifically for fail-safe microprocessor supervision in mission-critical systems where uncontrolled power loss could corrupt nonvolatile memory or cause unsafe hardware states.

FAQ

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

The MODE pin on the DS1231S-35+T&R configures the IN pin's electrical behavior: when tied to VCC, IN becomes a high-impedance input (VTP− = 2.15V) for resistor-divider AC sensing; when grounded, IN acts as a 30 µA current source (VTP+ = 2.5V) for direct opto-isolator interfacing. This dual-mode capability enables DS1231S-35+T&R to adapt to diverse power-loss detection topologies without redesign.

How does the DS1231S-35+T&R ensure reliable reset assertion during power-up?

The DS1231S-35+T&R guarantees a minimum 150 ms reset pulse on power-up, independent of VCC slew rate, by using an internal digital delay circuit synchronized to VCC stabilization. This ensures the microprocessor remains held in reset until all supply rails and clocks settle - a critical feature confirmed in DS1231S-35+T&R's AC Electrical Characteristics table under tRPU (150–1000 ms).

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

Yes - the DS1231S-35+T&R independently monitors AC-derived voltage at the IN pin (via MODE-configurable interface) and the +5V VCC rail. Its block diagram shows two separate comparators feeding NMI and RST outputs, allowing DS1231S-35+T&R to issue early warning (NMI) from upstream AC sag and final halt (RST) from downstream VCC dropout - delivering layered power-failure response.

What is the purpose of the TOL pin on the DS1231S-35+T&R?

The TOL pin on the DS1231S-35+T&R selects the VCC trip threshold: connecting TOL to GND sets VCCTP = 4.75V (±2%, typ.) for 5% tolerance systems; connecting TOL to VCC sets VCCTP = 4.25V for 10% tolerance. This single-pin configurability eliminates external resistors and makes DS1231S-35+T&R adaptable to varying power supply regulation specs.

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

Yes - the RST output is active-high push-pull and does not require a pull-up, but the RST output is active-low open-drain and must be pulled up to VCC (typically 4.7–10 kΩ). The DS1231S-35+T&R datasheet explicitly states "RST requires a pull-up resistor" in Figures 4–7 and AC Electrical Characteristics Note 5 - omission will prevent proper reset signaling to most microprocessors.