Analog Devices Inc./Maxim Integrated DS1231-35/G

Overview

DS1231-35/G from Maxim Integrated (now Analog Devices) is a precision power monitor IC designed to detect impending power failure and initiate orderly processor shutdown before VCC drops below 4.25V (–35% tolerance), provide non-maskable interrupt signaling via high-impedance or current-source input modes, and deliver dual active-high/active-low reset outputs with 150ms power-up delay. It operates at +5V supply, supports linear or switching power supplies, and requires no external capacitors.

For engineers reviewing the DS1231-35/G datasheet, DS1231-35/G pinout, DS1231-35/G application, or DS1231-35/G equivalent, key selection considerations include its dual VCC trip thresholds (4.25V/4.50V selectable via TOL pin), NMI generation timing (≤200µs after input threshold breach), RST/RST output drive capability (2.0mA sink, open-drain RST), and compatibility with opto-isolated or resistor-divider high-voltage sensing interfaces.

Technical Context

The DS1231-35/G integrates two independent comparators: one monitors VCC against a temperature-compensated reference to generate RST and RST signals at precise thresholds (4.25V ±0.12V when TOL=VCC), while the second monitors the IN pin using MODE-selectable input characteristics-high-impedance (≤0.1µA leakage) for resistor-divider AC-line sensing or 30µA current-source mode for opto-isolator interfacing with VTP+ = 2.5V.

Its internal digital sampler and delay logic ensure noise-immune operation with 60mV hysteresis on both comparators, and power-up reset timing guarantees ≥150ms RST assertion regardless of VCC slew rate. The device delivers simultaneous NMI and reset signals with defined propagation delays: tIPD ≤1.1µs (IN→NMI), tRPD ≤100ns (VCC detect→RST), and tRPU = 150–1000ms (VCC stable→RST release).

Key Specifications

Pinout & Package

DS1231-35/G is supplied in an 8-pin DIP package (300 mil width) with through-hole mounting. Pin 1 is IN (voltage sense input), Pin 2 is MODE (input configuration select), Pin 3 is TOL (VCC threshold select), Pin 4 is GND, Pin 5 is RST (active-high reset), Pin 6 is RST (active-low open-drain reset), Pin 7 is NMI (non-maskable interrupt), and Pin 8 is VCC (+5V supply). Pins labeled NC are unconnected.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX690CPA+ and TPS3823-33DBVR, the DS1231-35/G uniquely combines dual-threshold VCC monitoring, configurable high-voltage input sensing, and simultaneous NMI/reset signaling - enabling full power-failure response sequences rather than passive reset-only behavior.

Availability

DS1231-35/G is available at Aetrix Electronics and suitable for industrial PLC power supervision, medical device UPS handoff, and telecom line card power monitoring requiring stable component supply and long-term obsolescence management.

Supply support for DS1231-35/G 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 high-performance analog, mixed-signal, and power management ICs for precision measurement, industrial control, and reliable system supervision.

The DS1231-35/G belongs to Maxim's legacy power monitoring product line, engineered specifically for systems demanding deterministic power-failure response with early warning, automatic restart, and nonvolatile memory protection in 5V embedded environments.

FAQ

What is the exact VCC trip voltage for DS1231-35/G and how is it selected?

The DS1231-35/G has a nominal VCC trip voltage of 4.25V (–35% of 5V), specified as 4.25V ±0.12V. This threshold is selected by tying the TOL pin to VCC. If TOL is grounded, the trip point shifts to 4.50V (–10%). Both thresholds are internally generated using a temperature-compensated reference, and the DS1231-35/G datasheet confirms this behavior across 0°C to 70°C operating range.

How does the MODE pin affect the IN pin behavior in DS1231-35/G?

When MODE is tied to VCC, the IN pin (Pin 1) becomes a high-impedance input (≤0.1µA leakage), suitable for resistor-divider networks from AC lines or DC rails. When MODE is grounded, IN acts as a 30µA current source with VTP+ = 2.5V, enabling direct connection to opto-isolators. This dual-mode capability is explicitly documented in the DS1231-35/G functional description and timing diagrams.

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

Yes, DS1231-35/G requires an external pull-up resistor on the RST pin (Pin 6), which is an open-drain output. The RST pin (Pin 5) is push-pull and does not require a pull-up. The NMI pin (Pin 7) is also open-drain and requires its own pull-up. These requirements are stated in the "AC ELECTRICAL CHARACTERISTICS" table and application schematics in the DS1231-35/G datasheet.

What is the guaranteed minimum power-up reset duration for DS1231-35/G?

The DS1231-35/G guarantees a minimum power-up reset duration of 150ms, measured from the time VCC reaches 4.5V until RST is released. This value is specified in the "AC ELECTRICAL CHARACTERISTICS" table under parameter tRPU (min = 150ms, max = 1000ms), and applies across the full 0°C to 70°C temperature range per the DS1231-35/G datasheet.

Can DS1231-35/G monitor voltages higher than 5V, and how is that achieved?

Yes, DS1231-35/G can monitor voltages higher than 5V using external conditioning. When MODE = VCC, the IN pin accepts ≤5V, so a resistor divider scales high-voltage sense points (e.g., rectified AC) to ≤5V while maintaining VTP– = 2.15V for DS1231-35/G. When MODE = GND, a zener diode and opto-isolator interface handles >100V inputs. Both methods are validated in DS1231-35/G application figures 4–7.