Analog Devices Inc./Maxim Integrated DS1238S-5+

Overview

DS1238S-5+ from Maxim Integrated (now Analog Devices) is a microprocessor supervisory IC providing power-fail detection, watchdog reset control, non-maskable interrupt generation, SRAM backup switching, and battery-backed memory write protection. Key confirmed parameters: 4.5 V ±10% VCC trip point, 200 nA max battery current, 100 ms typical reset pulse width, 2.7 s internal watchdog timeout, and dual active-low/active-high RST outputs. It serves in industrial embedded systems requiring orderly shutdown during brownout.

For engineers reviewing the DS1238S-5+ datasheet, DS1238S-5+ pinout, DS1238S-5+ application, or DS1238S-5+ equivalent, this page delivers verified functional roles, exact timing thresholds, real-world SRAM backup behavior, watchdog strobe timing constraints, and precise early-warning voltage sense configuration - all validated against the official DS1238 datasheet Rev. 09152004.

Technical Context

The DS1238S-5+ integrates a bandgap voltage reference and precision comparator to monitor VCC with 10% tolerance (4.5 V nominal trip), generating RVT, RST (active low), and RST (active high) simultaneously on out-of-tolerance events. Its NMI output triggers at user-defined IN-pin voltage (1.27 V threshold) with built-in 30 kHz sampling and triple-sampling hysteresis to reject noise.

Watchdog operation uses either internal ring oscillator (2.7 s long period) or external clock/capacitor via OSCIN/OSCSEL; ST input requires high-to-low transition before timeout to prevent reset assertion. CEO output enables battery-backed SRAM write protection with 5 µs tCE delay to complete current memory cycle, while VCCO switches between VCC and VBAT with diode-drop isolation (VBAT–0.8 V min).

Key Specifications

Pinout & Package

DS1238S-5+ is supplied in a 16-pin SOIC (300-mil) package, pin-compatible with 16-pin DIP variants. All pins are electrically identical across packages; mechanical dimensions differ only in body outline and lead form.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar microprocessor supervisory applications.

Compared with MAX691ACPE+ and TPS3823-50DBVR, the DS1238S-5+ uniquely integrates NMI-triggered graceful shutdown, battery-switched SRAM backup with cycle-complete write protection, and field-programmable watchdog timing - making it irreplaceable in applications demanding deterministic data retention during power transients.

Availability

DS1238S-5+ is available at Aetrix Electronics and suitable for industrial data loggers, medical patient monitors, point-of-sale terminals, and programmable logic controllers requiring stable component supply and long-term lifecycle support.

Supply support for DS1238S-5+ 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 (via acquisition of Maxim Integrated) designs precision analog, mixed-signal, and power management ICs for high-reliability industrial, automotive, and medical systems.

The DS1238S-5+ belongs to Maxim's MicroManager family - engineered specifically to consolidate power monitoring, reset generation, watchdog supervision, and nonvolatile memory backup into a single 16-pin IC for space-constrained embedded controllers.

FAQ

What is the exact VCC trip voltage for DS1238S-5+?

The DS1238S-5+ has a guaranteed VCC trip point of 4.5 V ±0.13 V (min 4.25 V, max 4.50 V) under commercial temperature conditions. This 10% tolerance setting distinguishes it from the DS1238-5 variant (4.75 V trip). The trip is enforced by an internal bandgap reference and comparator, and directly controls RVT, RST, and CEO activation timing.

How does DS1238S-5+ prevent SRAM data corruption during power loss?

The DS1238S-5+ prevents SRAM data corruption by delaying CEO assertion for up to 5 µs (tCE) after VCC falls below 4.5 V, ensuring the current memory cycle completes before write protection engages. Simultaneously, VCCO switches from VCC to VBAT with ≤0.8 V drop, maintaining valid SRAM VDD. This dual-action - timed CE hold-off and seamless power switchover - is confirmed in the DS1238S-5+ datasheet Figure 7 and AC specs table.

Can DS1238S-5+ generate an early warning interrupt before reset?

Yes. The DS1238S-5+ generates a non-maskable interrupt (NMI) via its IN pin, which compares external voltage (set by resistor divider) to a 1.27 V internal reference. When the monitored voltage drops below this threshold, NMI activates after three consecutive 33 µs samples (~100 µs total), providing deterministic early warning before VCC reaches 4.5 V and triggers RST. This behavior is explicitly detailed in the "NON-MASKABLE INTERRUPT" section of the DS1238S-5+ datasheet.

What is the function of the ST pin on DS1238S-5+?

The ST (Strobe) pin on DS1238S-5+ resets the internal watchdog timer. A high-to-low transition must occur before the watchdog timeout period elapses (2.7 s typical with internal clock) to prevent WDS assertion and subsequent RST activation. If ST remains inactive, DS1238S-5+ forces RST and WDS low to recover unresponsive firmware - a critical safety feature confirmed in the "WATCHDOG TIMER" section and Table 1 of the DS1238S-5+ datasheet.

Does DS1238S-5+ support both active-low and active-high reset outputs?

Yes. DS1238S-5+ provides two dedicated reset outputs: RST (active low) and RST (active high), both asserted simultaneously when VCC falls below 4.5 V. The active-high RST is electrically isolated and complementary - not inverted - enabling direct interface with FPGA configuration pins, CPLD reset inputs, or other logic requiring positive-reset assertion, as shown in the Pin Assignment diagram and DC Electrical Characteristics table.