Analog Devices Inc./Maxim Integrated DS1231-50

Overview

DS1231-50 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 4.25V (–5% threshold with TOL = VCC). It provides dual reset outputs (RST active-high, RST active-low open-drain), NMI generation from high-voltage input monitoring, and automatic restart after power recovery. Used in industrial control systems with linear or switching supplies requiring nonvolatile memory protection.

For engineers reviewing the DS1231-50 datasheet, DS1231-50 pinout, DS1231-50 application, or DS1231-50 equivalent, key selection considerations include VCC trip accuracy (±0.12V at –5%), IN pin hysteresis (+60mV), dual-mode input sensing (high-Z or 30µA current source), 150ms power-up reset hold time, and compatibility with UL-approved opto-isolators for AC line monitoring.

Technical Context

The DS1231-50 integrates two independent comparators: one monitors VCC against a temperature-compensated reference to generate RST/RST at selectable 5% or 10% thresholds (TOL pin), while the second monitors external high-voltage inputs via Pin 1 to assert NMI based on MODE pin configuration (VCC or GND). Its digital delay circuit ensures precise timing between NMI warning and final reset assertion.

It operates across 4.5V–5.5V supply range with 0.5–2.0mA ICC, supports both transformer-isolated and opto-isolated AC sense topologies, and delivers 100ns VCC-detect-to-RST propagation delay with 1.1µs IN-to-NMI delay. The device requires no external capacitors and features built-in hysteresis for noise immunity on both input paths.

Key Specifications

Pinout & Package

DS1231-50 is supplied in an 8-pin DIP package (300 mil width) with through-hole mounting. Pin 1 is IN (voltage sense input), Pin 2 is MODE (input mode select), Pin 3 is TOL (VCC threshold select), Pin 4 is GND, Pin 5 is RST (active-high reset), Pin 6 is RST (active-low open-drain reset), Pin 7 is NMI (non-maskable interrupt), and Pin 8 is VCC (+5V supply).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690 and TPS3823-50, DS1231-50 uniquely combines early NMI warning, dual-mode high-voltage input sensing, and selectable VCC thresholds in a single 8-pin DIP-enabling complete power-failure response without additional discrete components or layout complexity.

Availability

DS1231-50 is available at Aetrix Electronics and suitable for industrial PLCs, medical UPS handoff systems, telecom shelf power management, and automotive infotainment head units requiring stable component supply and long-term lifecycle support.

Supply support for DS1231-50 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 (formerly Maxim Integrated) designs precision analog, mixed-signal, and power management ICs for industrial, automotive, and communications applications.

The DS1231-50 belongs to Maxim's legacy power monitoring product line, engineered specifically for systems requiring fail-safe shutdown and automatic recovery in mission-critical embedded environments.

FAQ

What is the exact VCC trip voltage for DS1231-50 when TOL is tied to VCC?

The DS1231-50 has a nominal VCC trip voltage of 4.25V when TOL is connected to VCC, corresponding to a –5% threshold relative to a 5.0V nominal supply. Per datasheet specifications, the actual trip range is 4.25V to 4.49V at 25°C, with tighter tolerance under industrial temperature conditions. This precise threshold ensures DS1231-50 initiates reset before downstream logic becomes unreliable.

How does the MODE pin affect the IN pin behavior in DS1231-50?

When MODE is tied to VCC, the IN pin (Pin 1) operates as a high-impedance input with VTP– = 2.3V trip point, suitable for resistor-divider interfaces to high-voltage sources. When MODE is grounded, IN becomes a 30µA current source with VTP+ = 2.5V, enabling direct connection to opto-isolator LEDs. DS1231-50's dual-mode architecture allows one device to serve both isolated and non-isolated sensing topologies without redesign.

Does DS1231-50 require external pull-up resistors on its reset outputs?

Yes, DS1231-50 requires an external pull-up resistor on Pin 6 (RST), which is an open-drain output. Pin 5 (RST) is push-pull and does not require a pull-up. Typical values range from 4.7kΩ to 10kΩ to +5V, selected based on bus capacitance and rise-time requirements. This design allows DS1231-50 to share reset buses with other open-drain devices while maintaining clean signal edges.

Can DS1231-50 monitor AC line voltage directly?

DS1231-50 cannot connect directly to AC mains but supports AC monitoring via external interface components. With MODE = GND, it drives opto-isolator LEDs using its 30µA current source; with MODE = VCC, it accepts scaled-down AC-derived DC via resistor dividers. DS1231-50's input stage is rated for ≤5V, so proper scaling and isolation-such as UL-approved optocouplers or transformer-based circuits-are mandatory for AC line safety compliance.

What is the minimum recommended hold time for DS1231-50 to ensure reliable NMI-to-RST sequencing?

DS1231-50 requires ≥200µs between NMI assertion and RST activation to allow firmware execution of critical save routines. This timing is guaranteed by internal digital delay circuitry and depends on the external power supply's hold-up time. For example, with a 1000µF/5V bulk capacitor discharging at 20mA, DS1231-50 provides ~250ms of warning-well exceeding the minimum. DS1231-50's design ensures this margin remains intact across temperature and supply variations.