Analog Devices Inc./Maxim Integrated DS1231-20+

Overview

DS1231-20+ from Maxim Integrated is a precision power monitor IC designed to detect impending power failure and initiate orderly processor shutdown before VCC drops below 4.75 V (5% threshold), provide non-maskable interrupt (NMI) on high-voltage input decay, and deliver 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 DS1231-20+ datasheet, DS1231-20+ pinout, DS1231-20+ application, or DS1231-20+ equivalent, key selection considerations include its dual-reset architecture (RST/RST), selectable 5%/10% VCC trip via TOL pin, high-impedance or current-source IN pin configurable by MODE, NMI timing response under voltage decay, and compatibility with microprocessor-based systems requiring fail-safe power sequencing.

Technical Context

The DS1231-20+ integrates two independent comparators: one monitors VCC against a temperature-compensated reference to generate RST and RST signals at 4.75 V (TOL = GND) or 4.50 V (TOL = VCC); the other monitors the IN pin with hysteresis-configured as high-impedance (MODE = VCC, VTP− = 2.3 V) or 30 µA current source (MODE = GND, VTP+ = 2.5 V). Both comparators feed digital samplers and delay logic to ensure noise-immune, deterministic timing.

Its internal power-up reset circuit holds RST/RST active for ≥150 ms after VCC reaches nominal, while power-down behavior unconditionally halts the processor before hold-up time exhaustion. The device supports opto-isolated AC line monitoring via MODE = GND configuration and direct DC rail sensing via MODE = VCC, enabling early warning at the highest possible point in the power chain.

Key Specifications

Pinout & Package

DS1231-20+ is supplied in an 8-pin DIP package (300 mil width), with pins 1–8 assigned as follows:

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS1231-20+, MAX690CPA+ offers lower cost but eliminates critical NMI-based shutdown orchestration, while TPS3823-50DBVR adds watchdog capability yet removes the core high-voltage sensing and dual-threshold architecture essential for robust power-fail prediction in industrial systems.

Availability

DS1231-20+ is available at Aetrix Electronics and suitable for industrial PLCs, medical UPS systems, telecom line cards, and automotive infotainment units requiring stable component supply across extended product lifecycles.

Supply support for DS1231-20+ 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 systems.

The DS1231-20+ belongs to Maxim's legacy power supervisor family, engineered specifically for fail-safe microprocessor systems requiring early power-failure detection, dual-reset signaling, and configurable high-voltage input interfaces.

FAQ

What is the exact VCC trip voltage for DS1231-20+ and how is it selected?

The DS1231-20+ has two factory-set VCC trip thresholds: 4.75 V (5% drop) when TOL is grounded, and 4.50 V (10% drop) when TOL is tied to VCC. These values are specified in the DC Electrical Characteristics table with ±0.12 V tolerance over 0°C to 70°C. The DS1231-20+ does not support intermediate thresholds - selection is strictly binary via the TOL pin connection.

Does DS1231-20+ require external pull-up resistors on its reset outputs?

DS1231-20+ RST (pin 5) is a push-pull output and requires no external pull-up. However, DS1231-20+ RST (pin 6) is an open-drain output and must be pulled up to VCC or another logic-compatible voltage using an external resistor (typically 4.7 kΩ–10 kΩ). This design allows DS1231-20+ RST to interface safely with mixed-voltage systems.

How does the MODE pin affect the IN pin behavior in DS1231-20+?

When MODE is connected to VCC, DS1231-20+ IN (pin 1) becomes a high-impedance input with 2.3 V trip threshold (VTP−) and <0.1 µA leakage - ideal for resistor-divider AC sensing. When MODE is grounded, DS1231-20+ IN sources 30 µA with 2.5 V trip (VTP+), enabling direct drive of opto-isolator LEDs. Both modes include 60 mV hysteresis for noise immunity.

Can DS1231-20+ monitor AC line voltage directly?

DS1231-20+ cannot connect directly to AC mains, but it can monitor rectified and filtered AC voltage via its IN pin. With MODE = VCC, a resistor divider scales the peak AC voltage to ≤5 V at IN, triggering NMI at 2.3 V. With MODE = GND, a zener-opto interface isolates the DS1231-20+ from high voltage - both methods are validated in Maxim's application notes for DS1231-20+.

What is the minimum power-up reset duration guaranteed by DS1231-20+?

DS1231-20+ guarantees a minimum power-up reset assertion time of 150 ms after VCC rises above 4.5 V, as confirmed in the AC Electrical Characteristics table. This interval is internally generated and independent of external components, ensuring reliable processor initialization even with slow-rising or noisy power rails.