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

Overview

DS1231S-35/T&R from Maxim Integrated (now Analog Devices) is a power monitor IC that detects impending power failure and initiates orderly processor shutdown before VCC drops below 4.25 V (–35% tolerance setting), provides dual active-high/active-low reset outputs, and generates non-maskable interrupt on input voltage decay. It operates from +5 V supply, supports both high-impedance and current-source input modes, and requires no external capacitors.

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 threshold accuracy (±2%, typ.), NMI propagation delay (1.1 µs), RST assertion timing (150–1000 ms power-up delay), and compatibility with linear or switching power supplies in embedded systems requiring fail-safe memory protection.

Technical Context

The DS1231S-35/T&R integrates two independent comparators: one monitors VCC against a temperature-compensated reference to assert RST/RST at 4.25 V (TOL = VCC), the other monitors IN pin voltage with hysteresis (±60 mV) and mode-selectable input characteristics (2.15 V trip when MODE = VCC; 2.5 V when MODE = GND). Both comparators feed digital samplers and delay logic to ensure noise-immune, deterministic timing.

Its internal architecture includes a precision bandgap reference, digital delay blocks for controlled reset assertion timing, and open-drain RST output with push-pull RST. The device supports dual power-fail detection paths-direct high-voltage sensing via resistor divider (MODE = VCC) or opto-isolated AC line monitoring (MODE = GND)-enabling early warning up to hundreds of milliseconds before VCC dropout.

Key Specifications

Pinout & Package

DS1231S-35/T&R is supplied in a 16-pin SOIC (300 mil) surface-mount package with 1.27 mm pitch. Pin 1 is located at the top-left corner adjacent to the notch or dot marking.

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/T&R uniquely combines VCC and high-voltage input monitoring, dual reset outputs, and programmable thresholds-enabling robust, multi-stage power-fail response in 5 V embedded systems without external timing components.

Availability

DS1231S-35/T&R is available at Aetrix Electronics and suitable for industrial control systems, medical instrumentation, point-of-sale terminals, and network infrastructure 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

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

The DS1231S-35/T&R belongs to Maxim's legacy Power Monitor family, engineered specifically for fail-safe microprocessor systems requiring deterministic power-fail detection, orderly shutdown, and automatic restart-targeting industrial, medical, and telecom equipment.

FAQ

What is the exact VCC trip threshold for DS1231S-35/T&R?

The DS1231S-35/T&R has a nominal VCC trip threshold of 4.25 V when the TOL pin is tied to VCC, corresponding to a –35% deviation from 5.0 V. Per datasheet DS1231/S page 7, the specified range is 4.25 V (min), 4.37 V (typ), and 4.49 V (max) at 0°C to +70°C. This threshold is temperature-compensated and applies directly to the DS1231S-35/T&R variant.

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

Yes, DS1231S-35/T&R requires an external pull-up resistor on the NMI and RST pins, both of which are open-drain outputs. The RST pin (pin 8) is push-pull and does not require a pull-up. Typical values range from 4.7 kΩ to 10 kΩ to +5 V, selected based on rise time and bus capacitance requirements per the DS1231S-35/T&R datasheet Figure 2 and AC Electrical Characteristics table.

How does the MODE pin affect DS1231S-35/T&R operation?

The MODE pin configures the IN pin (pin 1) behavior: when tied to VCC, DS1231S-35/T&R uses high-impedance sensing with a 2.15 V trip point; when tied to GND, it sources 30 µA for opto-isolator interfacing with a 2.5 V trip point. This dual-mode design allows DS1231S-35/T&R to support either resistor-divider or isolated AC monitoring without external components.

Can DS1231S-35/T&R replace a standard power-on reset IC?

Yes, DS1231S-35/T&R replaces basic reset ICs by providing enhanced functionality: it delivers power-on reset (150–1000 ms delay), power-fail warning (NMI), and dual reset outputs (RST/RST). Unlike simple reset ICs, DS1231S-35/T&R adds early fault detection and orderly shutdown capability-making it a functional superset for systems needing more than basic POR.

What is the maximum input voltage allowed on the IN pin of DS1231S-35/T&R?

The absolute maximum voltage on the IN pin of DS1231S-35/T&R is 5.0 V, as stated in the Absolute Maximum Ratings table (page 7). Exceeding this risks damage. When interfacing to higher voltages (e.g., rectified AC), a resistor divider must scale the sense voltage to ≤5.0 V at the IN pin-verified in the Application section (Figure 4) of the DS1231S-35/T&R datasheet.