Analog Devices Inc./Maxim Integrated DS1231S-20+T&R

Overview

DS1231S-20+T&R from Maxim Integrated (now Analog Devices) is a power monitor IC that detects impending AC/DC power failure and triggers orderly microprocessor shutdown before VCC drops below 4.75 V (–5% threshold), provides non-maskable interrupt (NMI) on input voltage decay, and delivers dual active-high/active-low reset outputs with 150 ms power-up delay. It operates from +5 V supply, supports linear or switching power supplies, and requires no external capacitors.

For engineers reviewing the DS1231S-20+T&R datasheet, DS1231S-20+T&R pinout, DS1231S-20+T&R application, or DS1231S-20+T&R equivalent, key selection criteria include VCC trip accuracy (±5% at 4.75 V), IN pin dual-mode interface (high-Z or 30 µA current source), NMI timing (≤200 µs response), RST/RST output drive capability (2–3 mA sink), and SOIC-16 package compatibility with industrial temperature range (–40°C to +85°C).

Technical Context

The DS1231S-20+T&R integrates two independent comparators: one monitors VCC against a temperature-compensated reference to assert RST/RST at 4.75 V (TOL = GND) or 4.5 V (TOL = VCC); the other monitors the high-voltage input (IN) with mode-selectable hysteresis (VTP+ = 2.5 V or VTP– = 2.3 V) to generate NMI. Its digital sampler and delay logic ensure deterministic timing between NMI assertion and final RST activation.

It features dual-reset architecture: RST is push-pull (active-high, VOH ≥ VCC–0.1 V), while RST is open-drain (active-low, requires pull-up). The MODE pin configures IN as either high-impedance (≤0.1 µA leakage) for resistor-divider sensing or 30 µA current source for opto-isolator interfacing-enabling early detection upstream of the regulated +5 V rail.

Key Specifications

Pinout & Package

DS1231S-20+T&R is housed in a 16-pin SOIC (300 mil) surface-mount package with 1.27 mm pitch and standard JEDEC MS-012AC footprint. Pin 1 is located at the top-left corner adjacent to the index notch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690TSA+ and TPS3823-50DBVR, the DS1231S-20+T&R uniquely delivers dual-stage warning (NMI + RST/RST), configurable input interface, and no-external-component operation-making it the only choice for systems requiring both early fault detection and robust reset sequencing across isolated power domains.

Availability

DS1231S-20+T&R is available at Aetrix Electronics and suitable for industrial PLCs, telecom line cards, medical diagnostic devices, and embedded data loggers requiring stable component supply with guaranteed long-term availability and traceable sourcing.

Supply support for DS1231S-20+T&R 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

Analog Devices (formerly Maxim Integrated) designs precision analog, mixed-signal, and power management ICs for high-reliability industrial, automotive, and communications systems.

The DS1231S-20+T&R belongs to Maxim's legacy power supervision product line, engineered specifically for systems demanding fail-safe power-failure response with minimal external components and galvanic isolation support.

FAQ

What is the exact VCC trip voltage for DS1231S-20+T&R and how is it selected?

The DS1231S-20+T&R has two selectable VCC trip thresholds: 4.75 V (–5% of nominal 5 V) when the TOL pin is grounded, and 4.5 V (–10%) when TOL is tied to VCC. This selection is implemented via an internal resistor ladder and reference comparator. The –20 suffix confirms the device is calibrated for the 4.75 V threshold under standard conditions, and DS1231S-20+T&R maintains this specification across its full operating temperature range (–40°C to +85°C) with ±2% typical variation.

Does DS1231S-20+T&R require external pull-up resistors, and if so, on which pins?

Yes, DS1231S-20+T&R requires an external pull-up resistor on the RST pin (Pin 8), which is an open-drain output. The RST pin (Pin 5) is push-pull and does not require a pull-up. Typical pull-up values range from 4.7 kΩ to 10 kΩ to +5 V, sized to ensure sufficient rise time (<1 µs) while limiting current to ≤1 mA. No pull-up is needed on NMI (Pin 7), as it is also open-drain but typically driven into a CMOS input with adequate internal termination.

Can DS1231S-20+T&R interface directly with AC mains voltage?

No, DS1231S-20+T&R cannot connect directly to AC mains. Its IN pin (Pin 1) accepts maximum 5 V DC. To monitor AC line voltage, DS1231S-20+T&R must be used with external conditioning: either a resistor divider (when MODE = VCC) to scale rectified/filtered AC to ≤5 V, or a UL-approved opto-isolator (when MODE = GND) to provide galvanic isolation. Figure 5 and Figure 7 in the official datasheet show validated implementations for both approaches using DS1231S-20+T&R.

What is the purpose of the MODE pin on DS1231S-20+T&R, and how does it affect system design?

The MODE pin (Pin 2) configures the electrical behavior of the IN pin (Pin 1): when tied to VCC, IN becomes a high-impedance (≤0.1 µA) input for use with passive resistor dividers; when grounded, IN sources 30 µA to drive opto-isolator LEDs. This dual-mode capability allows DS1231S-20+T&R to support both cost-sensitive direct-sensing and safety-certified isolated architectures without redesign-making MODE a critical layout decision that determines whether external biasing components are needed.

Is DS1231S-20+T&R RoHS compliant and lead-free?

Yes, DS1231S-20+T&R is RoHS compliant and lead-free. It meets EU Directive 2011/65/EU and is manufactured with matte tin (Sn) lead finish on the SOIC-16 package. The "+T&R" suffix denotes tape-and-reel packaging compliant with EIA-481 standards, and the device carries the "+" marking per Maxim/Analog Devices' green product labeling convention-confirming full exemption from lead, cadmium, mercury, hexavalent chromium, PBB, and PBDE substances.