Analog Devices Inc./Maxim Integrated DS1231-20

Overview

DS1231-20 from Maxim Integrated (now Analog Devices) is a precision power monitor IC designed to detect impending power failure and initiate orderly microprocessor shutdown. It features dual comparators for independent monitoring of high-voltage input (IN) and +5V supply (VCC), selectable 5% or 10% VCC trip thresholds via TOL pin, active-high and open-drain RST outputs, and NMI generation - all in an 8-pin DIP package. It is used in industrial control systems where nonvolatile memory integrity must be preserved during AC line sags or brownouts.

For engineers reviewing the DS1231-20 datasheet, DS1231-20 pinout, DS1231-20 application, or DS1231-20 equivalent, key selection considerations include its dual-threshold VCC detection (4.75V/4.5V), IN pin mode-selectable hysteresis (VTP±2.3V/2.5V), 150 ms power-up reset hold time, and compatibility with both linear and switching power supplies without external capacitors.

Technical Context

The DS1231-20 integrates two independent comparators: one monitors VCC against temperature-compensated reference voltages (4.75V at TOL=GND, 4.5V at TOL=VCC), generating RST (active-high) and RST (open-drain) signals; the other monitors the high-impedance IN pin (2.3V threshold when MODE=VCC) to trigger NMI before VCC collapse. Its internal digital delay ensures deterministic timing between NMI assertion and RST activation.

It supports two input sensing modes: MODE=VCC enables ultra-low-leakage (<0.1 µA) voltage-divider interfacing to AC-derived sense points; MODE=GND configures IN as a 30 µA current source (VTP+=2.5V) for opto-isolator coupling. Hysteresis is fixed at ±60 mV for noise immunity in both modes.

Key Specifications

Pinout & Package

DS1231-20 is supplied in an 8-pin plastic DIP (300 mil) package with through-hole mounting. Pin 1 is IN; Pin 2 is MODE; Pin 3 is TOL; Pin 4 is GND; Pin 5 is RST (active-high); Pin 6 is RST (open-drain); Pin 7 is NMI; Pin 8 is 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 MAX690 and TPS3823-50, the DS1231-20 uniquely delivers predictive power-failure response via dual-path monitoring, enabling deterministic data preservation - a capability absent in simpler reset supervisors that react only after supply failure.

Availability

DS1231-20 is available at Aetrix Electronics and suitable for industrial control systems, medical diagnostics equipment, financial transaction terminals, and telecom infrastructure requiring stable component supply across extended production lifecycles.

Supply support for DS1231-20 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, automotive, and communications applications.

The DS1231-20 belongs to Maxim's Power Monitoring and Supervisory family, engineered specifically to prevent data corruption in microprocessor-based systems during power transients and brownouts.

FAQ

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

The MODE pin on the DS1231-20 selects the electrical behavior of the IN pin: when tied to VCC, IN becomes a high-impedance input (leakage <0.1 µA) for resistor-divider sensing; when grounded, IN acts as a 30 µA current source for opto-isolator interfacing. This dual-mode capability allows the DS1231-20 to adapt to either direct AC-line monitoring or isolated high-voltage detection schemes without external components.

How does the DS1231-20 provide early warning of power failure?

The DS1231-20 provides early warning by monitoring a high-voltage sense point (e.g., rectified AC) at the IN pin, which trips NMI well before the +5V rail collapses. For example, with MODE=VCC and a 2.3V threshold, it can detect AC sag 200 µs before VCC drops below 4.75V - giving the system time to save data before RST activates. This predictive capability is intrinsic to the DS1231-20's dual-comparator architecture.

What are the VCC trip thresholds supported by the DS1231-20?

The DS1231-20 supports two precise VCC trip thresholds: 4.75V (5% drop from nominal 5.0V) when the TOL pin is grounded, and 4.5V (10% drop) when TOL is connected to VCC. These thresholds are internally generated using a temperature-compensated reference and are guaranteed over 0°C to +70°C - a core specification defining DS1231-20's reliability in power supervision.

Does the DS1231-20 require external capacitors for reset timing?

No, the DS1231-20 does not require external capacitors for reset timing. Its 150 ms power-up reset hold time and deterministic NMI-to-RST delay are implemented using internal digital sampling and reference circuitry. This eliminates capacitor aging, temperature drift, and board space concerns - a key design advantage of the DS1231-20 over RC-based reset generators.

Can the DS1231-20 replace standard power-up reset ICs?

Yes, the DS1231-20 replaces basic power-up reset ICs while adding critical functionality: it provides not only a guaranteed 150 ms reset on power-up but also real-time VCC monitoring and predictive NMI generation during power-down. Unlike simple reset ICs, the DS1231-20 actively safeguards nonvolatile memory by halting the processor *before* VCC violates specification - a capability built into every DS1231-20 device.