Analog Devices Inc./Maxim Integrated DS2227-120

Overview

DS2227-120 from Dallas Semiconductor (now Maxim Integrated) is a 4-Mbit nonvolatile static RAM module in a 72-pin SIP Stik format, organized as 512k × 8, 256k × 16, or 128k × 32 bits, with 120 ns access time, >10-year data retention without VCC, and integrated dual lithium batteries for seamless power-loss protection. It serves as drop-in NV SRAM replacement in industrial memory subsystems requiring persistent storage during brownouts or shutdown.

For engineers reviewing the DS2227-120 datasheet, DS2227-120 pinout, DS2227-120 application, or DS2227-120 equivalent, key selection considerations include JEDEC 72-pin SIMM compatibility, automatic write-protection below 4.25 V, battery status detection via read-write-verify sequence, and bank-select flexibility across four independent SRAM banks.

Technical Context

The DS2227-120 implements fully transparent nonvolatile operation: all backup logic, voltage monitoring, and lithium switching circuitry operate autonomously without host intervention. Its four independent memory banks each have dedicated CE/OE/WE pins, enabling configurable byte/word/long-word access granularity and flexible bus-width mapping.

Power management is hardware-driven: at VCC < 4.25 V, write protection activates; below ~3.0 V, internal power switch connects lithium source to retain data; above ~3.0 V on power-up, external VCC resumes control. Battery redundancy uses two isolated lithium cells with automatic selection of the higher-voltage cell.

Key Specifications

Pinout & Package

DS2227-120 uses a 72-pin SIP (Single In-line Package) Stik form factor (4.25" × 0.85") compliant with JEDEC standard SIMM socket mounting. Pin layout supports four independent 128k × 8 SRAM banks, each with dedicated control and data terminals.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar nonvolatile SRAM applications.

Compared with STK12C68 and DS1248, the DS2227-120 uniquely combines 4-bank selectability, dual-lithium redundancy, and battery health verification-making it optimal for high-availability systems where memory corruption risk must be minimized across decades of field operation.

Availability

DS2227-120 is available at Aetrix Electronics and suitable for industrial PLC data logging, medical device configuration storage, and avionics black box recorders requiring stable component supply and long-term lifecycle support.

Supply support for DS2227-120 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

Dallas Semiconductor, acquired by Maxim Integrated in 2001, specialized in precision analog, nonvolatile memory, and real-time clock ICs for mission-critical embedded systems.

The DS2227-120 belongs to the Flexible NV SRAM Stik product line, designed specifically to replace volatile SRAM in legacy systems while delivering guaranteed data retention during indefinite power loss-targeting aerospace, medical, and industrial control applications.

FAQ

What is the memory organization flexibility of the DS2227-120?

The DS2227-120 supports three configurations: 512k × 8, 256k × 16, or 128k × 32 bits. This is achieved by externally tying data lines and control signals across its four independent 128k × 8 banks. No internal register programming is required-the DS2227-120's flexibility is purely hardware-wired, enabling reuse across multiple system architectures without firmware changes.

How does the DS2227-120 detect low battery voltage?

The DS2227-120 performs automatic battery voltage checking on every power-up. If the lithium supply falls below 2.0 V, the second memory access is inhibited. Users verify battery health via a three-step process: read any location, write new data to that location, then re-read-if the written value fails to appear, the DS2227-120 battery is depleted and data retention is no longer assured.

Does the DS2227-120 require external components for nonvolatile operation?

No. The DS2227-120 integrates all necessary circuitry-including voltage monitoring, lithium switching, and dual battery management-within the 72-pin SIP Stik package. Unlike discrete NV SRAM solutions, the DS2227-120 needs no external capacitors, regulators, or backup controllers to achieve >10-year data retention without VCC.

What is the significance of the "-120" suffix in DS2227-120?

The "-120" suffix denotes the access time specification: 120 ns maximum tACC and tRC. This distinguishes it from faster variants (DS2227-70 and DS2227-100) and confirms timing compliance for systems operating at up to ~8.3 MHz synchronous bus rates. All DS2227-120 units share identical pinout, organization, and nonvolatile functionality-only speed grade differs.

Can the DS2227-120 be used in place of standard SRAM without design changes?

Yes-the DS2227-120 is functionally transparent during normal operation: it behaves identically to a standard 512k × 8 SRAM with identical timing, pinout, and control protocol. The nonvolatile features activate automatically only during power loss, so existing SRAM interfaces, drivers, and timing constraints remain fully valid for the DS2227-120.