Analog Devices Inc./Maxim Integrated DS1231-35+

Overview

DS1231-35+ from Maxim Integrated (now Analog Devices) is a precision power monitor IC designed to detect impending power failure and initiate orderly processor shutdown before VCC drops below 4.37 V (–35% tolerance setting), provide non-maskable interrupt signaling via high-impedance or current-source input modes, and deliver dual active-high/active-low reset outputs with 150 ms power-up delay. It operates from +5 V supply, supports linear or switching power supplies, and requires no external capacitors.

For engineers reviewing the DS1231-35+ datasheet, DS1231-35+ pinout, DS1231-35+ application, or DS1231-35+ equivalent, key selection considerations include its dual-reset architecture (RST and RST), selectable 5% or 10% VCC threshold via TOL pin, mode-selectable input interface (high-Z or 30 µA current source), NMI generation timing, and industrial temperature range support (–40°C to +85°C).

Technical Context

The DS1231-35+ integrates two independent comparators: one monitors VCC against a temperature-compensated reference to assert RST/RST at 4.37 V (TOL = VCC), while the other monitors the IN pin-configured via MODE pin-to generate NMI when input voltage crosses VTP+ (2.5 V, MODE = GND) or VTP– (2.15 V, MODE = VCC). Hysteresis of ±60 mV ensures noise immunity on both inputs.

Its digital sampler and delay logic coordinate timing between NMI warning and final reset assertion, ensuring maximum usable hold-up time from the power supply. The device automatically holds reset active for ≥150 ms on power-up and releases NMI only after both VCC stabilization and IN threshold achievement, preventing spurious interrupts during brown-out recovery.

Key Specifications

Pinout & Package

DS1231-35+ is supplied in an 8-pin DIP package (300 mil width), with pin 1 as IN, pin 2 as MODE, pin 3 as TOL, pin 4 as GND, pin 5 as RST (active-high push-pull), pin 6 as RST (active-low open-drain), pin 7 as NMI (open-drain), and pin 8 as VCC. All NC pins are 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 MAX690TSA+ and TPS3823-50DBVR, the DS1231-35+ uniquely delivers coordinated NMI warning + dual-reset assertion + configurable input interface - making it irreplaceable in designs requiring predictive power-failure response and isolation-ready sensing.

Availability

DS1231-35+ is available at Aetrix Electronics and suitable for industrial PLC controllers, telecom power shelves, medical diagnostic equipment, and energy metering gateways requiring stable component supply and long-term lifecycle assurance.

Supply support for DS1231-35+ 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 (acquired by Analog Devices in 2021) is a semiconductor company specializing in analog, mixed-signal, and power management solutions for industrial, communications, and computing markets.

The DS1231-35+ belongs to Maxim's legacy power supervision product line, engineered specifically for systems demanding deterministic power-failure response, nonvolatile memory protection, and robust interface flexibility across isolated and non-isolated topologies.

FAQ

What is the exact VCC trip voltage for DS1231-35+ under standard operating conditions?

The DS1231-35+ has a nominal VCC trip point of 4.37 V when the TOL pin is connected to VCC, corresponding to a –35% threshold relative to 5.0 V. This value is specified across 0°C to +70°C with typical tolerance of ±0.12 V (4.25 V to 4.49 V), and remains stable over temperature due to its internal temperature-compensated reference circuit. DS1231-35+ uses this precise threshold to initiate reset before downstream logic becomes unreliable.

How does the MODE pin affect the input behavior of DS1231-35+?

The MODE pin on DS1231-35+ selects between two distinct input configurations: when tied to VCC, Pin 1 becomes a high-impedance input with 2.15 V trip point (VTP–), ideal for resistor-divider sensing of AC-derived voltages; when tied to GND, Pin 1 sources 30 µA and trips at 2.5 V (VTP+), enabling direct connection to opto-isolator LEDs. DS1231-35+ leverages this dual-mode capability to support both non-isolated and UL-approved isolated monitoring architectures without external components.

Does DS1231-35+ require external pull-up resistors on its outputs?

DS1231-35+ requires an external pull-up resistor only on the RST (Pin 6) output, which is open-drain. The RST (Pin 5) output is push-pull and drives high actively, so no pull-up is needed. The NMI (Pin 7) output is also open-drain and requires a pull-up for proper logic-level assertion. DS1231-35+ documentation specifies standard 4.7 kΩ pull-ups for 5 V systems, ensuring fast rise times and noise margin compliance.

Can DS1231-35+ operate in industrial temperature environments?

Yes, DS1231-35+ is rated for operation from –40°C to +85°C, meeting industrial temperature requirements. This rating is confirmed in the Absolute Maximum Ratings table and validated across DC and AC electrical specifications. DS1231-35+ maintains full functionality-including accurate VCC trip points, consistent NMI timing, and stable reset delays-throughout this extended range, making it suitable for deployment in harsh environments like factory floors and outdoor telecom cabinets.

What is the power-up reset duration guaranteed by DS1231-35+?

DS1231-35+ guarantees a minimum reset pulse width of 150 ms on power-up, holding both RST and RST active until VCC stabilizes within specification. This timing is independent of external components and built into the internal digital delay block. DS1231-35+ ensures reliable microprocessor initialization by preventing clock or instruction fetch until the 5 V rail reaches steady-state, eliminating race conditions during cold start.