Analog Devices Inc./Maxim Integrated DS1231-50+

Overview

DS1231-50+ from Maxim Integrated is a power monitor IC that detects impending AC/DC power failure and initiates orderly microprocessor shutdown before VCC drops below 4.25V (–5% threshold), provides non-maskable interrupt (NMI) on input voltage decay, and delivers dual active-high/active-low reset outputs with 150ms power-up delay. It operates from +5V supply, supports linear or switching power supplies, and requires no external capacitors.

For engineers reviewing the DS1231-50+ datasheet, DS1231-50+ pinout, DS1231-50+ application, or DS1231-50+ equivalent, key selection considerations include VCC trip accuracy (±5% at 4.25V), IN pin dual-mode interface (high-Z or 30µA current source), NMI timing (≤200µs response), and compatibility with 8-pin DIP or 16-pin SOIC packages in industrial temperature range.

Technical Context

The DS1231-50+ integrates two independent comparators: one monitors VCC against a precision temperature-compensated reference to generate RST/RST signals at selectable 4.25V (TOL=VCC) or 4.50V (TOL=GND) thresholds; the other monitors high-voltage input (IN) with mode-selectable hysteresis (VTP+ = 2.5V or VTP– = 2.3V) to assert NMI before main rail collapse.

Its digital sampler and delay logic ensure deterministic timing: tRPU = 150–1000ms for reset assertion on power-up, tRPD ≤100ns for fast reset activation during power-down, and tIPU ≤200µs for NMI propagation - all while maintaining noise immunity via built-in hysteresis and supporting opto-isolated or resistor-divider sensing topologies.

Key Specifications

Pinout & Package

DS1231-50+ is packaged in an 8-pin DIP (300 mil) with through-hole mounting. Pin functions are validated per DS1231/S datasheet Rev. 022698.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690CPA+ and TPS3823-50DBVR, DS1231-50+ uniquely delivers predictive power-loss detection via its configurable IN pin and dual-reset architecture, enabling true orderly shutdown - not just reset assertion - making it irreplaceable in systems requiring data integrity during brownouts.

Availability

DS1231-50+ is available at Aetrix Electronics and suitable for industrial automation, telecom infrastructure, medical diagnostics, and embedded control systems 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

Maxim Integrated (now part of Analog Devices) is a semiconductor company specializing in analog, mixed-signal, and power management ICs for industrial, automotive, and communications markets.

The DS1231-50+ belongs to Maxim's legacy power supervision product line, designed specifically for systems demanding reliable, predictive power failure response with minimal external components and industrial-grade robustness.

FAQ

What is the exact VCC trip voltage for DS1231-50+ and how is it selected?

The DS1231-50+ has a nominal VCC trip voltage of 4.25V (–5% of 5V), confirmed by the "-50" suffix and datasheet Section 1 specifying TOL=VCC configuration. This threshold is selected by connecting the TOL pin to VCC; connecting TOL to GND changes the trip point to 4.50V (–10%). The DS1231-50+ datasheet guarantees 4.25–4.49V tolerance across temperature and supply variations, ensuring consistent early-warning behavior before 5V rail violation.

Does DS1231-50+ require external pull-up resistors, and if so, on which pins?

Yes, DS1231-50+ requires an external pull-up resistor on the RST (pin 6) output, which is an open-drain active-low signal. The datasheet explicitly states "RST requires a pull–up resister" in Figures 4–7 and notes "RST is an open drain output" in AC Electrical Characteristics. No pull-up is needed for RST (pin 5), as it is push-pull active-high. NMI (pin 7) is also push-pull and does not require external biasing. The DS1231-50+ itself contains no internal pull-ups.

Can DS1231-50+ monitor AC line voltage directly, and what interface is required?

No, DS1231-50+ cannot monitor AC line voltage directly due to its 5V absolute maximum input rating on the IN pin. It requires interface circuitry: either a resistor divider (for Mode=VCC configuration) to scale high-voltage AC-derived DC to ≤5V at IN, or an opto-isolator (for Mode=GND configuration) with zener clamping to safely translate AC loss events. Both methods are validated in DS1231/S Application Notes Figures 4–7. DS1231-50+ provides the sensing logic but relies on external components for safe high-voltage coupling.

What is the function of the MODE pin on DS1231-50+, and how does it affect the IN pin?

The MODE pin on DS1231-50+ configures the electrical behavior of the IN pin (pin 1). When MODE is tied to VCC, IN becomes a high-impedance input (IIL ≤0.1µA) with VTP– = 2.3V trip point, optimized for resistor-divider sensing. When MODE is grounded, IN becomes a 30µA current source with VTP+ = 2.5V, enabling direct connection to opto-isolator LEDs. This dual-mode capability allows DS1231-50+ to adapt to different isolation strategies without redesign - a core feature distinguishing it from simpler reset ICs.

Is DS1231-50+ compatible with 3.3V systems, or is it strictly a 5V device?

DS1231-50+ is strictly a +5V device: its recommended operating VCC is 4.5–5.5V, and all specifications (including VCC trip points, output drive strength, and input thresholds) are defined only for 5V operation. It does not support 3.3V supply or logic levels. Attempting to operate DS1231-50+ at 3.3V will result in incorrect trip thresholds, insufficient output drive, and undefined behavior. For 3.3V systems, a dedicated 3.3V supervisor like MAX6326–33 must be used instead of DS1231-50+.