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-freshness sealing in embedded systems. It features 4.75 V ±5% VCC trip point, dual active-high/active-low RST outputs, 200 nA battery current, and 16-pin SOIC packaging. Used in industrial controllers for orderly shutdown during brownouts.

For engineers reviewing the DS1238S-5 datasheet, DS1238S-5 pinout, DS1238S-5 application, or DS1238S-5 equivalent, key selection criteria include precise 5% supply monitoring threshold, dual-reset output polarity support, integrated SRAM VCCO switching, watchdog timeout configurability via OSCSEL/OSCIN, and NMI-driven early warning capability before VCC collapse.

Technical Context

The DS1238S-5 implements a bandgap-referenced comparator for accurate 5% VCC monitoring (VCCTP = 4.75 V typ), with RVT indicating threshold breach and dual RST outputs asserting after ≥40 µs propagation delay. Its watchdog timer supports internal (2.7 s typical) or external clock sources, resettable via ST strobe, and latches timeout status on WDS.

It integrates a bidirectional SRAM power switch (VCCO) that seamlessly transitions between VCC and VBAT, with CEO write-protection delayed until CEI returns high or tCE (5 µs) expires - preventing memory corruption mid-cycle. The IN/NMI path uses 3-cycle hysteresis sampling at ~30 kHz to reject noise while detecting user-defined voltage decay thresholds (VTP = 1.27 V).

Key Specifications

Pinout & Package

DS1238S-5 is housed in a 16-pin SOIC (300-mil) package with standard DIP-compatible footprint. Pin functions are electrically identical across SOIC and DIP variants per datasheet mechanical drawings.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX691ACPE+ and TPS3823-50DBVR, DS1238S-5 uniquely integrates 5% precision monitoring, NMI-driven firmware intervention, SRAM VCCO switching with tCE delay, and programmable watchdog - making it the sole choice for systems requiring coordinated power-fail response with data integrity guarantees.

Availability

DS1238S-5 is available at Aetrix Electronics and suitable for industrial PLC controllers, medical data loggers, telecom line cards, and smart energy meters requiring stable component supply across extended temperature ranges and long product lifecycles.

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 (formerly Maxim Integrated) is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving industrial, automotive, communications, and healthcare markets.

The DS1238S-5 belongs to Maxim's MicroManager family of supervisory ICs, engineered specifically for robust power management and fault recovery in mission-critical microprocessor systems operating under harsh electrical conditions.

FAQ

What is the exact VCC trip point for DS1238S-5 and how is it guaranteed?

The DS1238S-5 has a guaranteed 5% VCC trip point of 4.75 V (min), 4.62 V (typ), and 4.75 V (max) per its DC Electrical Characteristics table. This is achieved using a precision bandgap voltage reference and comparator circuit, with production testing verifying VCCTP across temperature and process corners. DS1238S-5 maintains this specification over 0°C to +70°C operation, ensuring consistent reset behavior in systems with tight supply tolerances.

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

Yes, DS1238S-5 provides two independent reset outputs: one active-low (RST) and one active-high (RST), both asserted concurrently when VCC falls below the 4.75 V trip point. Each output meets specified VOL ≤ 0.4 V and VOH ≥ VCC−0.5 V, enabling direct interface with microprocessors requiring either polarity - such as Intel x86 (active-low) and ARM Cortex-M (active-high) families - without external inverters.

How does the DS1238S-5 prevent SRAM data corruption during power failure?

DS1238S-5 prevents SRAM data corruption by delaying CEO assertion until either CEI returns high or the 5 µs tCE timeout expires - ensuring the current memory write cycle completes before write-protection engages. Simultaneously, VCCO switches to VBAT before VCC drops below 2.7 V, maintaining SRAM power. This dual mechanism is validated in Figure 7 of the DS1238 datasheet and ensures zero-cycle data loss during brownout events.

Can the watchdog timer in DS1238S-5 be disabled, and if so, how?

Yes, the DS1238S-5 watchdog timer can be disabled by leaving the ST pin open (high-impedance), which tri-states the internal watchdog circuit. Alternatively, driving ST high continuously also disables timeout behavior. Once disabled, WDS remains inactive unless VCC falls below VCCTP. This disable method is documented in the "WATCHDOG TIMER" section (page 3) and requires no configuration registers or software commands - purely hardware-controlled.

What is the purpose of the freshness seal function in DS1238S-5 and how is it activated?

The freshness seal in DS1238S-5 electrically disconnects the battery during storage/shipping to prevent capacity loss. It is activated by applying three precisely timed negative pulses (≤ –3 V, 100 ns wide, 1 µs spacing) to the IN pin while VCC is at nominal 5 V - as shown in Figure 8. Upon activation, VCCO, RST, RST, and CEO enter tri-state, while WDS goes low. DS1238S-5 exits freshness mode automatically upon VCC power cycle above VBAT, restoring full functionality.