Analog Devices Inc./Maxim Integrated DS1231S-35

Overview

DS1231S-35 from Maxim Integrated (now Analog Devices) is a precision power monitor IC designed to detect impending power failure and initiate orderly processor shutdown. It provides dual reset outputs (RST active-high, RST active-low open-drain), NMI generation, 5% or 10% VCC threshold detection (4.25V or 4.50V 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 datasheet, DS1231S-35 pinout, DS1231S-35 application, or DS1231S-35 equivalent, key selection considerations include VCC trip point accuracy (±5% at 4.25V), input mode flexibility (Mode pin selects VTP+ or VTP−), NMI-to-RST timing margin, dual-reset interface compatibility, and SOIC-16 package suitability for space-constrained embedded designs.

Technical Context

The DS1231S-35 integrates two independent comparators: one monitors VCC against a temperature-compensated reference to assert RST/RST when voltage falls below a selectable threshold (TOL pin selects 4.25V or 4.50V), while the second monitors the IN pin using Mode-selectable input characteristics - sourcing 30 µA for opto-isolator interfacing (Mode = GND) or presenting >1 MΩ impedance for resistor-divider AC sense networks (Mode = VCC).

It delivers deterministic timing behavior: tRPU (power-up reset pulse width) is 150–1000 ms; tRPD (VCC detect to RST assertion) is 100 ns; tIPD (IN detect to NMI) is 1.1 µs; and hysteresis is fixed at ±60 mV on both comparators. The device operates across 0°C to +70°C, draws 0.5–2.0 mA ICC, and requires no external capacitors for basic operation.

Key Specifications

Pinout & Package

DS1231S-35 is housed in a 16-pin SOIC (300 mil) package with 1.27 mm pitch, JEDEC MS-012AC compliant, and rated for 0°C to +70°C operation. Pin 1 is IN; Pin 2 is MODE; Pin 3 is TOL; Pin 4 is GND; Pins 5 and 6 are RST (active-high) and RST (active-low open-drain); Pin 7 is NMI; Pin 8 is VCC; remaining pins are NC.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690SAA+ and TPS3823-33DBVR, the DS1231S-35 uniquely combines VCC and high-voltage input monitoring with dual reset outputs and NMI - enabling firmware-driven graceful shutdown in 5V industrial systems where early power-loss warning is mandatory.

Availability

DS1231S-35 is available at Aetrix Electronics and suitable for industrial PLCs, medical UPS handoff circuits, telecom shelf supervisors, and smart energy meter designs requiring stable component supply and long-term lifecycle assurance.

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, is a semiconductor company specializing in precision analog, mixed-signal, and power management ICs for industrial, automotive, and communications applications.

The DS1231S-35 belongs to Maxim's Power Monitoring and Supervisory family, engineered specifically for systems requiring deterministic, multi-stage power-failure response with hardware-enforced timing margins and isolation-ready interface flexibility.

FAQ

What is the exact VCC trip voltage for DS1231S-35 when TOL is tied to VCC?

The DS1231S-35 has a nominal VCC trip voltage of 4.25V when the TOL pin is connected to VCC, with a guaranteed tolerance of ±5% (4.04V to 4.46V) over 0°C to +70°C. This value is derived from the device's internal temperature-compensated reference and is confirmed in the DC Electrical Characteristics table on page 7 of the official datasheet. The DS1231S-35 maintains this accuracy without calibration or external components.

How does the MODE pin affect the input pin (Pin 1) behavior in DS1231S-35?

When MODE is tied to VCC, Pin 1 of the DS1231S-35 becomes a high-impedance input (<0.1 µA leakage), optimized for resistor-divider networks sensing AC-derived voltages. When MODE is grounded, Pin 1 sources 30 µA, enabling direct connection to opto-isolator LEDs. This dual-mode capability is intrinsic to the DS1231S-35's architecture and allows flexible, standards-compliant isolation without external biasing components.

Does DS1231S-35 require external pull-up resistors, and if so, on which pins?

Yes, the DS1231S-35 requires an external pull-up resistor on the RST (Pin 6) output, which is an open-drain active-low signal. The RST (Pin 5) output is push-pull and does not require a pull-up. No pull-up is needed on NMI (Pin 7), as it is also push-pull. Typical pull-up values range from 4.7 kΩ to 10 kΩ to +5V, as specified in application schematics for the DS1231S-35.

What is the minimum recommended hold-up time margin between NMI assertion and RST assertion in DS1231S-35 applications?

The DS1231S-35 provides a guaranteed minimum NMI-to-RST margin of 200 µs under typical conditions, based on tIPU (200 µs max VCC detect to NMI) and tRPU (150 ms min power-up reset width). In power-down scenarios, the margin depends on system hold-up time but is architecturally maximized by decoupling IN and VCC monitoring paths - a core design feature of the DS1231S-35 that enables reliable firmware execution windows.

Is DS1231S-35 compatible with 3.3V microcontrollers, or is it strictly a 5V device?

The DS1231S-35 is a +5V-only device: its VCC operating range is 4.5V to 5.5V, and its outputs (RST, RST, NMI) swing rail-to-rail within that domain. It is not 3.3V tolerant on any pin. To interface with 3.3V microcontrollers, level-shifting circuitry is required on RST, RST, and NMI lines - a constraint explicitly documented in the Absolute Maximum Ratings and DC Electrical Characteristics sections for the DS1231S-35.