Analog Devices Inc./Maxim Integrated DS1231S-50

Overview

DS1231S-50 from Maxim Integrated (now Analog Devices) is a precision power monitor IC designed for early power-failure detection and controlled system shutdown in 5V microprocessor systems. It provides dual reset outputs (RST active-high, RST active-low open-drain), NMI generation, selectable 5% or 10% VCC threshold detection, and high-impedance or current-source input modes - enabling robust AC-line or DC-rail monitoring in industrial controllers and embedded systems.

For engineers reviewing the DS1231S-50 datasheet, DS1231S-50 pinout, DS1231S-50 application, or DS1231S-50 equivalent, key selection criteria include VCC trip accuracy (±5% at 4.50–4.74V), IN pin hysteresis (60 mV), NMI-to-RST timing margin (≥200 µs), and compatibility with both linear and switching power supplies without external capacitors.

Technical Context

The DS1231S-50 integrates two independent comparators: one monitors VCC against a temperature-compensated reference to generate RST/RST signals at programmable thresholds (4.50V or 4.25V), while the second monitors the IN pin using MODE-selectable input characteristics - high-impedance (≤0.1 µA leakage) when MODE = VCC or 30 µA current source when MODE = GND. Both paths include built-in hysteresis (60 mV) for noise immunity.

Its digital sampler and delay logic ensure RST remains asserted ≥150 ms on power-up and unconditionally halts the processor before VCC drops below 2.0V. The device operates across 0°C to 70°C, draws ≤2.0 mA ICC, and supports direct opto-isolator interfacing via the IN pin in MODE = GND configuration.

Key Specifications

Pinout & Package

DS1231S-50 is housed in a 16-pin SOIC (300 mil) surface-mount package. Pin assignments are validated per Maxim DS1231/S datasheet Rev. 022698.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX692AESA+ and TPS3808G18DBVR, the DS1231S-50 uniquely combines early NMI warning, dual-reset signaling, and MODE-selectable high-voltage sensing - making it irreplaceable in systems requiring coordinated hardware-initiated shutdown before power collapse.

Availability

DS1231S-50 is available at Aetrix Electronics and suitable for industrial control panels, medical diagnostic instruments, telecom line cards, and automotive infotainment systems requiring stable component supply and long-term lifecycle support.

Supply support for DS1231S-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, designs precision analog and mixed-signal ICs for power management, sensing, and interface applications in industrial, medical, and communications markets.

The DS1231S-50 belongs to Maxim's legacy Power Monitor family - engineered specifically to replace discrete reset circuits and provide deterministic, hardware-enforced shutdown sequencing in 5V microprocessor systems.

FAQ

What is the exact VCC trip voltage range for DS1231S-50 when TOL is grounded?

The DS1231S-50 exhibits a VCC trip voltage range of 4.50V to 4.74V when TOL is connected to GND - corresponding to a 5% tolerance around nominal 5V. This specification is measured over 0°C to 70°C and ensures reset activation occurs before the 5V rail falls outside industry-standard ±5% limits. The DS1231S-50 maintains this accuracy via an internal temperature-compensated reference, eliminating need for external calibration.

Does DS1231S-50 require external pull-up resistors on its RST and NMI outputs?

Only the RST pin (pin 6) requires an external pull-up resistor because it is an open-drain output. The RST pin (pin 5) is a push-pull output and drives actively high or low without external components. NMI (pin 7) is also push-pull and does not need a pull-up. The DS1231S-50 datasheet explicitly states "RST requires a pull-up resistor" - confirming that only one of the three control outputs needs external biasing.

How does the MODE pin affect the input characteristics of DS1231S-50's IN pin (pin 1)?

When MODE (pin 2) is tied to VCC, the IN pin (pin 1) becomes a high-impedance input (<0.1 µA leakage), suitable for resistor-divider networks sensing AC-derived voltages. When MODE is grounded, IN becomes a 30 µA current source - enabling direct connection to opto-isolator LEDs. This dual-mode operation is intrinsic to the DS1231S-50's architecture and allows safe high-voltage monitoring without redesigning the front-end circuit.

Can DS1231S-50 operate with a 3.3V supply?

No, the DS1231S-50 is specified exclusively for 5V operation: its recommended VCC range is 4.5V to 5.5V, and all electrical characteristics - including VCC trip points, output drive strength, and IN pin thresholds - are characterized only at 5V. Using 3.3V will cause failure to assert RST/NMI at correct thresholds and may result in undefined behavior. For 3.3V systems, a different power monitor such as the MAX6369 must be selected - the DS1231S-50 is not compatible.

What is the minimum guaranteed reset pulse width on DS1231S-50 during power-up?

The DS1231S-50 guarantees a minimum reset pulse width of 150 ms on power-up, measured from VCC crossing 1.0V to RST deassertion. This timing is independent of supply slew rate and ensures sufficient hold time for all supported 5V microprocessors to initialize reliably. The DS1231S-50 achieves this via internal digital sampling and delay logic - no external capacitor is needed to set this duration.