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

Overview

DS1231S-20/T&R from Maxim Integrated (now Analog Devices) is a precision power monitor IC designed to detect impending power failure and initiate orderly microprocessor shutdown. It provides dual reset outputs (RST active-high, RST active-low open-drain), NMI generation, 5% VCC threshold detection (4.75 V trip), and supports both high-impedance and current-source input modes via MODE pin selection - used in industrial control systems with linear or switching power supplies.

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 considerations include VCC monitoring accuracy, NMI timing response (1.1 µs IN-to-NMI delay), dual-reset interface compatibility, and support for opto-isolated AC line sensing without external capacitors.

Technical Context

The DS1231S-20/T&R integrates two independent comparators: one monitors VCC against a temperature-compensated reference to generate RST/RST at 4.75 V (TOL = GND), and another monitors the IN pin with programmable hysteresis (±60 mV) and mode-selectable input characteristics (2.3 V threshold when MODE = VCC; 2.5 V when MODE = GND). Its digital sampler and delay logic ensure deterministic timing between NMI assertion and final reset activation.

It operates across 0°C to +70°C, draws 0.5–2.0 mA supply current, and features rail-to-rail output drive capability - RST delivers 2.0–3.0 mA sink current at 0.4 V, while RST maintains VOH ≥ VCC–0.5 V under 500 µA load. The device requires no external timing capacitors and supports direct interface to UL-approved opto-isolators or resistor-divider networks.

Key Specifications

Pinout & Package

DS1231S-20/T&R is housed in a 16-pin SOIC package (300 mil width), RoHS-compliant, tape-and-reel format (T&R). Pin 1 is IN; Pin 2 is MODE; Pin 3 is TOL; Pin 4 is GND; Pins 5 and 6 are RST (active-high) and RST (active-low open-drain); Pin 7 is NMI; Pin 8 is VCC. Pins 9–16 are NC (no internal connection).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690CSA+ and TPS3808G33DBVR, DS1231S-20/T&R uniquely combines VCC brownout detection, early NMI warning, dual-reset signaling, and high-voltage input flexibility - making it the only option among the three capable of implementing full power-failure response protocols in 5 V industrial systems.

Availability

DS1231S-20/T&R is available at Aetrix Electronics and suitable for industrial PLCs, medical UPS handoff systems, and telecom line cards requiring stable component supply, long-term lifecycle support, and traceable sourcing for safety-critical designs.

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

Maxim Integrated (acquired by Analog Devices in 2021) designs precision analog and mixed-signal ICs for industrial, automotive, and communications applications, emphasizing reliability, integration, and performance under harsh conditions.

The DS1231S-20/T&R belongs to Maxim's legacy power supervision product line, engineered specifically for systems requiring deterministic, multi-stage power-failure response - including early warning, controlled shutdown, and glitch-free restart - in environments with noisy or unstable power sources.

FAQ

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

The DS1231S-20/T&R has a nominal VCC trip voltage of 4.75 V (–5% of 5 V), selected by grounding the TOL pin (Pin 3). When TOL is tied to VCC, the trip shifts to 4.25 V (–10%). This dual-threshold capability allows designers to match the DS1231S-20/T&R to specific power supply hold-up time requirements and system-level brownout margins without redesigning the PCB layout.

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 RST (Pin 6), as it is an open-drain output. RST (Pin 5) is push-pull and does not require a pull-up. The NMI (Pin 7) output is also open-drain and must be pulled up externally. Typical values range from 4.7 kΩ to 10 kΩ to +5 V, sized to meet the target µP's input leakage and rise-time requirements while minimizing power draw.

How does the MODE pin affect the IN pin behavior in DS1231S-20/T&R?

In DS1231S-20/T&R, the MODE pin (Pin 2) configures the IN pin (Pin 1) as either a high-impedance input (MODE = VCC; leakage ≤0.1 µA) or a 30 µA current source (MODE = GND). The former enables simple resistor-divider AC sensing; the latter allows direct connection to opto-isolator LEDs. This dual-mode architecture lets DS1231S-20/T&R serve both low-cost and safety-isolated applications without external bias components.

What is the minimum recommended hold time for DS1231S-20/T&R to guarantee proper reset assertion during power-down?

DS1231S-20/T&R asserts RST and RST within 100 ns of VCC crossing the trip threshold (tRPD = 100 ns), and maintains reset until VCC falls below 2.0 V. To ensure reliable operation, the power supply must sustain VCC ≥2.0 V for ≥10 µs after trip - a condition met by most 5 V supplies with ≥100 µF bulk capacitance. This timing behavior is explicitly characterized in the DS1231S-20/T&R datasheet and verified across temperature.

Can DS1231S-20/T&R be used with 3.3 V microcontrollers, and what interface considerations apply?

DS1231S-20/T&R is a 5 V-only device and cannot directly monitor or interface with 3.3 V systems. Its VCC pin requires 4.5–5.5 V, and its outputs swing relative to that rail. To use DS1231S-20/T&R with a 3.3 V µP, level-shifting circuitry (e.g., dual-supply translator or resistor-divider + buffer) is required on RST, RST, and NMI lines - adding complexity that negates the DS1231S-20/T&R's integrated advantage. For 3.3 V systems, consider purpose-built supervisors like TPS3808G33DBVR instead.