Analog Devices Inc./Maxim Integrated DS1231-20N

Overview

DS1231-20N from Maxim Integrated (now Analog Devices) is a precision power monitor IC designed to detect impending power failure and initiate orderly microprocessor shutdown before VCC drops below specification. It provides dual reset outputs (RST active-high, RST active-low open-drain), NMI generation from high-voltage input sensing, 5% or 10% VCC threshold detection via TOL pin, and automatic restart after power recovery - deployed in industrial control systems with linear or switching supplies.

For engineers reviewing the DS1231-20N datasheet, DS1231-20N pinout, DS1231-20N application, or DS1231-20N equivalent, this page delivers verified functional roles, confirmed timing behavior (tRPU = 150–1000 ms, tRPD = 100 ns), exact VCC trip points (4.25 V @ TOL=VCC, 4.50 V @ TOL=GND), and validated interface requirements including mandatory external pull-up on RST.

Technical Context

The DS1231-20N integrates two independent comparators: one monitors VCC against temperature-compensated reference thresholds (selectable 5% or 10% via TOL), generating synchronized RST and RST signals; the other monitors high-impedance or current-source IN pin (configured by MODE) to trigger NMI up to 200 µs before VCC failure. Its digital sampler and delay logic ensure noise-immune operation with 60 mV hysteresis on IN.

It replaces discrete power-up reset circuitry by delivering guaranteed 150 ms minimum reset assertion on power-up, supports both transformer-isolated and opto-isolated AC line monitoring, and requires no external capacitors - enabling direct integration into 8-pin DIP or 16-pin SOIC layouts without timing component dependencies.

Key Specifications

Pinout & Package

DS1231-20N is supplied in an 8-pin DIP package (300 mil width), with pins 1–8 assigned as follows:

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690EPA+ and TPS3823-50DBVR, DS1231-20N uniquely combines early NMI warning, dual-reset signaling, and configurable high-voltage input sensing - making it irreplaceable where deterministic shutdown sequencing and isolation-compliant AC monitoring are required.

Availability

DS1231-20N is available at Aetrix Electronics and suitable for industrial automation, medical device power supervision, and telecom shelf management requiring stable component supply and long-term lifecycle support.

Supply support for DS1231-20N 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 (acquired by Analog Devices in 2021) designs precision analog and mixed-signal ICs for power, sensing, and interface applications in industrial, medical, and communications markets.

The DS1231-20N belongs to Maxim's legacy power monitoring product line, engineered specifically for deterministic power-failure response in safety-critical embedded systems using 5 V logic rails.

FAQ

What is the function of the MODE pin on the DS1231-20N?

The MODE pin on the DS1231-20N selects the electrical behavior of the IN pin: when tied to VCC, IN becomes a high-impedance input (VTP− = 2.3 V) for resistor-divider sensing; when grounded, IN sources 30 µA (VTP+ = 2.5 V) to drive opto-isolator LEDs. This dual-mode capability enables DS1231-20N to interface safely with both isolated and non-isolated power inputs without external components.

Does the DS1231-20N require external pull-up resistors?

Yes - the DS1231-20N's RST pin is an open-drain output and requires an external pull-up resistor to VCC (typically 4.7 kΩ–10 kΩ) to generate a valid active-low reset signal. RST is push-pull and does not require pull-up, but NMI also benefits from a pull-up for noise immunity in long-trace applications. DS1231-20N datasheet Figure 2 confirms this requirement explicitly.

What is the guaranteed reset pulse width on power-up for the DS1231-20N?

The DS1231-20N guarantees a minimum reset assertion time of 150 ms (tRPU) on power-up, ensuring sufficient stabilization of the +5 V supply before releasing the processor. Maximum duration is 1000 ms under worst-case conditions. This timing is internally generated and does not depend on external capacitors - a key differentiator of DS1231-20N versus discrete reset ICs.

Can the DS1231-20N monitor voltages higher than 5 V directly?

No - the DS1231-20N's IN pin has an absolute maximum rating of VCC + 0.5 V (≤5.5 V). To monitor higher voltages (e.g., AC line or 24 V DC), DS1231-20N must be used with external circuitry: a resistor divider for MODE=VCC operation or a zener/opto-isolator network for MODE=GND. The DS1231-20N itself only processes conditioned signals within its 0–5 V input range.

How does the TOL pin affect the DS1231-20N's VCC detection threshold?

The TOL pin on the DS1231-20N selects between two factory-trimmed VCC trip thresholds: connecting TOL to GND sets VCCTP = 4.50–4.74 V (–5% of 5 V), while connecting TOL to VCC sets VCCTP = 4.25–4.49 V (–10%). These ranges are specified in the DS1231-20N's DC Electrical Characteristics table and determine the exact voltage at which RST and RST activate during brownout.