Analog Devices Inc./Maxim Integrated DS1231S-20+

Overview

DS1231S-20+ from Maxim Integrated is a power monitor IC that detects impending AC/DC power failure and initiates orderly microprocessor shutdown before VCC drops below 4.75V (5% threshold), provides non-maskable interrupt (NMI) via high-impedance input sensing, and delivers dual active-high/active-low reset outputs with 150ms power-up delay. It operates from +5V supply, requires no external capacitors, and supports both linear and switching power supplies.

For engineers reviewing the DS1231S-20+ datasheet, DS1231S-20+ pinout, DS1231S-20+ application, or DS1231S-20+ equivalent, this device serves as a precision VCC and high-voltage input monitor for embedded systems requiring fail-safe power sequencing, nonvolatile memory protection, and automatic restart after brownout recovery.

Technical Context

The DS1231S-20+ integrates two independent comparators: one monitors VCC against a temperature-compensated reference to generate RST/RST at selectable 5% (4.75V) or 10% (4.5V) thresholds, and the other monitors the IN pin with mode-selectable input characteristics-high-impedance (Mode=VCC, VTP−=2.3V) or current-source (Mode=GND, VTP+=2.5V, 30µA sink).

Its digital sampler and delay logic ensure NMI triggers well before RST activation, maximizing available hold-up time for processor shutdown. The device features built-in hysteresis (±60mV), open-drain RST output requiring external pull-up, and guaranteed operation across 0°C to 70°C with 0.5–2.0mA supply current.

Key Specifications

Pinout & Package

DS1231S-20+ is housed in a 16-pin SOIC (300 mil) surface-mount package with 1.27mm pitch and JEDEC MS-013AC footprint.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690EPA+ and TPS3823-50DBVR, the DS1231S-20+ uniquely combines dual-reset signaling, programmable VCC threshold, and mode-configurable high-voltage input sensing-enabling full power-fail response (early warning + controlled shutdown + safe restart) in a single chip.

Availability

DS1231S-20+ is available at Aetrix Electronics and suitable for industrial PLCs, medical diagnostic devices, telecom line cards, and embedded network routers requiring stable component supply and long-term lifecycle support.

Supply support for DS1231S-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 power management, sensing, and communication applications.

The DS1231S-20+ belongs to Maxim's legacy power monitoring product line, engineered specifically for fail-safe microprocessor systems needing coordinated power-fail warning, reset generation, and nonvolatile memory protection in harsh electrical environments.

FAQ

What is the exact VCC trip voltage for DS1231S-20+ when TOL is grounded?

The DS1231S-20+ has a nominal VCC trip voltage of 4.75V (5% below 5.0V) when the TOL pin is connected to GND. Per datasheet page 7, the specified range is 4.50V to 4.74V at 0°C to 70°C, ensuring reliable reset assertion before microprocessor operational limits are exceeded. This threshold is maintained by an internal temperature-compensated reference circuit within the DS1231S-20+.

Does DS1231S-20+ require external pull-up resistors on its reset outputs?

Yes, DS1231S-20+ requires an external pull-up resistor on the RST (pin 6) output because it is an open-drain driver. The RST (pin 5) output is push-pull and does not require a pull-up. Typical values range from 4.7kΩ to 10kΩ to +5V, selected based on rise-time requirements and bus loading. This design allows DS1231S-20+ to share the RST signal line with other open-drain devices in multi-IC systems.

How does the MODE pin affect the input behavior of DS1231S-20+?

When MODE is tied to VCC, DS1231S-20+ configures its IN pin (pin 1) as a high-impedance input with a 2.3V trip point (VTP−), ideal for resistor-divider-based AC line monitoring. When MODE is grounded, DS1231S-20+ makes IN a 30µA current source with a 2.5V trip point (VTP+), enabling direct connection to opto-isolators or switched inputs. This dual-mode flexibility is intrinsic to the DS1231S-20+ architecture.

Can DS1231S-20+ monitor voltages higher than 5V directly?

No, DS1231S-20+ cannot monitor voltages above 5V directly on its IN pin-the absolute maximum rating is VCC + 0.5V. However, DS1231S-20+ supports high-voltage monitoring indirectly: with MODE=VCC, a resistor divider scales down AC/DC rails (e.g., 120VAC rectified) to ≤5V at IN; with MODE=GND, a zener-opto network references the trip point to high-side voltage. Both methods are validated in DS1231S-20+ application schematics.

What is the power-up reset timing behavior of DS1231S-20+?

DS1231S-20+ holds both RST and RST outputs active for a minimum of 150ms after VCC rises above 4.5V, per datasheet AC Electrical Characteristics table. This guaranteed delay ensures the +5V supply stabilizes before releasing the microprocessor from reset. The timing is internally generated and does not depend on external components-making DS1231S-20+ suitable for systems requiring deterministic power-on sequencing without added passive elements.