Analog Devices Inc./Maxim Integrated DS1231-35

Overview

DS1231-35 from Maxim Integrated is a precision power monitor IC designed to detect impending power failure and initiate orderly processor shutdown before VCC drops below 4.25 V (–35% tolerance), provide non-maskable interrupt (NMI) on input voltage decay, and deliver dual active-high/active-low reset outputs with 150 ms power-up delay. It supports both high-impedance and current-source input modes and operates across 4.5 V to 5.5 V supply.

For engineers reviewing the DS1231-35 datasheet, DS1231-35 pinout, DS1231-35 application, or DS1231-35 equivalent, key selection considerations include its dual VCC trip thresholds (4.25 V / 4.75 V), NMI generation timing (200 µs response), input mode flexibility (MODE pin-selectable), open-drain RST output requiring pull-up, and compatibility with linear or switching supplies in embedded industrial systems.

Technical Context

The DS1231-35 integrates two independent comparators: one monitors VCC against a temperature-compensated reference to assert RST/RST at selectable 5% or 10% undervoltage thresholds, while the second monitors the IN pin with MODE-selectable hysteresis (VTP+ = 2.5 V or VTP− = 2.15 V). Its digital sampler and delay logic ensure deterministic reset assertion timing during power-down transitions.

It features no external capacitor requirement, internal biasing for both comparator paths, and dual reset outputs-RST (push-pull, active-high) and RST (open-drain, active-low)-enabling direct interface to diverse microprocessor reset inputs. The TOL pin selects between 4.25 V (TOL = VCC) and 4.75 V (TOL = GND) trip points, validated per DC electrical specs at 0°C to 70°C.

Key Specifications

Pinout & Package

DS1231-35 is supplied in an 8-pin DIP package (300 mil width), with pin 1 designated as IN, pin 2 as MODE, pin 3 as TOL, pin 4 as GND, pin 5 as RST (active-high), pin 6 as RST (active-low, open-drain), pin 7 as NMI, and pin 8 as VCC. All NC pins are internally unconnected and must remain floating.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690T and TPS3808G33, DS1231-35 uniquely delivers simultaneous dual-reset outputs, hardware-selectable VCC trip points, and a dedicated NMI signal with sub-millisecond latency - making it optimal for systems requiring coordinated firmware-initiated shutdown prior to power collapse.

Availability

DS1231-35 is available at Aetrix Electronics and suitable for industrial PLCs, medical diagnostic devices, telecom line cards, and automotive infotainment systems requiring stable component supply and long-term lifecycle support.

Supply support for DS1231-35 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 DS1231-35 belongs to Maxim's legacy power-monitoring product line, engineered specifically for systems needing deterministic power-fail detection, early-warning interrupts, and dual-mode reset signaling in harsh or safety-critical environments.

FAQ

What is the exact VCC trip voltage for DS1231-35 and how is it set?

The DS1231-35 has a nominal VCC trip voltage of 4.25 V, corresponding to a –35% deviation from 5 V. This threshold is selected by connecting the TOL pin to VCC. When TOL = GND, the trip point shifts to 4.75 V (–5%). Both thresholds are specified with ±0.12 V tolerance over 0°C to 70°C and are derived from an internal temperature-compensated reference, ensuring stability across operating conditions. DS1231-35's datasheet confirms this value in the DC Electrical Characteristics table under VCCTP (TOL = VCC).

How does the MODE pin affect DS1231-35's input behavior on Pin 1?

When MODE is tied to VCC, DS1231-35 configures Pin 1 as a high-impedance input (leakage <0.1 µA) with VTP− = 2.15 V, suitable for resistor-divider networks sensing AC-derived voltages. When MODE is grounded, Pin 1 becomes a 30 µA current source with VTP+ = 2.5 V, enabling direct connection to opto-isolators or switched inputs. DS1231-35's dual-mode architecture allows flexible interfacing to either isolated or non-isolated power rails without external components.

Does DS1231-35 require external pull-up resistors, and if so, on which pins?

Yes, DS1231-35 requires an external pull-up resistor on Pin 6 (RST), because it is an open-drain, active-low output. Pin 5 (RST) is push-pull and does not require a pull-up. The datasheet specifies that RST must be pulled up to VCC with a resistor typically between 4.7 kΩ and 10 kΩ to ensure proper logic levels and drive strength. No pull-up is needed on NMI (Pin 7), which is push-pull active-high. DS1231-35's design eliminates pull-ups on all other pins, including IN and MODE.

What is the guaranteed power-up reset duration for DS1231-35, and why is it important?

DS1231-35 guarantees a minimum 150 ms power-up reset pulse on both RST and RST outputs after VCC rises above 4.25 V. This duration ensures the microprocessor remains held in reset long enough for the power supply to stabilize, clock oscillators to settle, and internal registers to initialize - preventing erratic boot behavior. DS1231-35's internal timing circuit enforces this delay regardless of VCC slew rate, making it robust against slow-ramping or noisy supplies commonly found in industrial systems.

Can DS1231-35 be used with 3.3 V systems, or is it strictly a 5 V device?

DS1231-35 is specified exclusively for 5 V operation: its absolute maximum VCC rating is +7.0 V, and recommended operating range is 4.5 V to 5.5 V. The internal reference, comparator thresholds, and output drive levels are calibrated for 5 V rails. It cannot reliably monitor or interface with 3.3 V systems - attempting to operate DS1231-35 at 3.3 V will result in incorrect trip points, weak output drive, and potential functional failure. For 3.3 V applications, a purpose-built supervisor like MAX6326 should be selected instead of DS1231-35.