Analog Devices Inc./Maxim Integrated DS1231S-20N

Overview

DS1231S-20N from Maxim Integrated (now Analog Devices) is a precision power monitor IC that detects impending power failure by monitoring both high-voltage input (IN) and +5V supply (VCC), generating NMI and dual RST signals to enable orderly processor shutdown and automatic restart. It supports 5% VCC threshold detection (TOL = GND), operates from 4.5V to 5.5V, delivers 100 ns VCC-to-RST propagation delay, and requires no external capacitors. Used in industrial control systems with linear or switching power supplies.

For engineers reviewing the DS1231S-20N datasheet, DS1231S-20N pinout, DS1231S-20N application, or DS1231S-20N equivalent, key selection considerations include its dual-reset outputs (active-high and open-drain), selectable 5%/10% VCC trip thresholds, high-impedance or current-source IN pin configuration, and compatibility with opto-isolated AC line sensing for early power-loss warning.

Technical Context

The DS1231S-20N integrates two independent comparators: one monitors VCC against a temperature-compensated reference to assert RST/RST at 4.75V (–5% threshold) when TOL = GND, and another monitors the IN pin-configured as high-impedance (VTP– = 2.3V, Mode = VCC) or 30 µA current source (VTP+ = 2.5V, Mode = GND). Its digital sampler and delay logic ensure noise-immune hysteresis (±60 mV) and precise timing alignment between NMI assertion and final reset.

On power-up, DS1231S-20N holds RST/RST active for ≥150 ms to allow supply stabilization; on power-down, it triggers NMI first (tIPU = 200 µs), then RST/RST (tRPD = 100 ns) just before hold-up time exhaustion. The device supports UL-approved opto-isolator interfacing via Mode = GND and tolerates input voltages up to 5V on Pin 1, with absolute max ratings of –0.5V to +7.0V on VCC and –0.5V to VCC+0.5V on I/O pins.

Key Specifications

Pinout & Package

DS1231S-20N is housed in a 16-pin SOIC (300-mil) surface-mount package with 0.050" lead pitch and JEDEC MS-013AC compliance. Pin 1 is IN; Pins 5 and 6 are RST (active-high) and RST (open-drain); Pin 7 is NMI; Pin 3 is TOL; Pin 2 is MODE; Pins 4, 8, 11, 13, and 15 are NC; Pin 9 is VCC; Pin 16 is GND.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690SAA+ and TPS3823-50DBVR, DS1231S-20N uniquely provides both early NMI warning and dual-reset coordination, enabling deterministic firmware-controlled shutdown - essential for systems where data integrity depends on precise timing between power-failure detection and processor halt.

Availability

DS1231S-20N is available at Aetrix Electronics and suitable for industrial automation, medical diagnostics, and telecom infrastructure requiring stable component supply, long-term lifecycle support, and guaranteed traceability for safety-critical deployments.

Supply support for DS1231S-20N 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 industrial, medical, and communications applications, emphasizing reliability, low power, and integration.

The DS1231S-20N belongs to Maxim's Power Monitoring family, engineered specifically to replace discrete reset circuits in 5V microprocessor systems while adding intelligent, multi-stage power-failure response - not just reset generation but predictive warning and coordinated shutdown.

FAQ

What is the function of the MODE pin on the DS1231S-20N?

The MODE pin on the DS1231S-20N configures the IN pin's electrical behavior: when tied to VCC, IN becomes a high-impedance (≤0.1 µA) 2.3V threshold comparator ideal for resistor-divider AC sensing; when grounded, IN sources 30 µA to drive opto-isolator LEDs, enabling isolated high-voltage monitoring. This dual-mode capability makes DS1231S-20N adaptable to both direct and isolated power-failure detection topologies without external components.

How does the DS1231S-20N differ from standard reset ICs like the MAX809?

Unlike basic reset ICs such as the MAX809-which only monitor VCC and assert a single reset-the DS1231S-20N adds an independent high-voltage IN pin with configurable sensing, generates both NMI and dual RST outputs, and implements intelligent timing sequencing (NMI first, then RST) to enable firmware-controlled shutdown. DS1231S-20N also replaces power-up reset circuitry with built-in ≥150 ms timing, eliminating external RC networks required by simpler supervisors.

Can the DS1231S-20N be used with a 3.3V system?

No-the DS1231S-20N is specified only for 4.5V to 5.5V operation and monitors a 5V VCC rail; its internal reference, comparators, and output drivers are designed for TTL/CMOS 5V logic levels. Using it with a 3.3V supply violates absolute maximum ratings and will result in incorrect trip thresholds and potential damage. For 3.3V systems, consider purpose-built supervisors like the MAX6369 or TPS3808.

What is the purpose of the two RST outputs on the DS1231S-20N?

The DS1231S-20N provides RST (active-high, push-pull) and RST (open-drain) to support different system-level reset architectures: RST directly drives a microprocessor's synchronous reset input, while RST allows wired-OR connection with other system resets (e.g., watchdog or manual reset) on a shared bus. This dual-output design enables flexible reset coordination without additional logic, and DS1231S-20N ensures both signals activate simultaneously within 100 ns of VCC violation.

Does the DS1231S-20N require external passive components for basic operation?

No-DS1231S-20N requires no external capacitors or resistors for core functionality: its internal reference, timing delays, and hysteresis are fully integrated. Only application-specific components are needed: a pull-up resistor on RST (per datasheet note), and optional voltage-divider resistors on IN when using Mode = VCC. This eliminates BOM count and layout complexity compared to discrete supervisor solutions, making DS1231S-20N a true drop-in replacement for legacy reset circuits.