Analog Devices Inc./Maxim Integrated DS1225AD-70

Overview

DS1225AD-70 from Maxim Integrated is a 64k-bit (8k × 8) nonvolatile static RAM with integrated lithium battery backup, 70 ns access time, ±10% V_CC tolerance (4.5–5.5 V), and industrial temperature rating (–40°C to +85°C). It replaces volatile SRAMs and EEPROMs in memory-critical embedded systems requiring data retention during power loss.

For engineers reviewing the DS1225AD-70 datasheet, DS1225AD-70 pinout, DS1225AD-70 application, or DS1225AD-70 equivalent, key selection considerations include its automatic write-protection at V_TP = 4.25–4.5 V, 10-year data retention without external power, JEDEC-standard 28-pin 720-mil DIP package, and direct pin compatibility with 2764 EPROM and 2864 EEPROM.

Technical Context

The DS1225AD-70 implements a self-contained power-fail detection circuit that monitors V_CC continuously; when voltage drops below ~4.25 V, it disables writes and switches to lithium backup at ~3.0 V. Its CMOS architecture supports unlimited write cycles and requires no external support circuitry for microprocessor interfacing.

It operates in three distinct modes: read (CE & OE low, WE high), write (CE & WE low), and data retention (V_CC < 3.0 V, lithium active, all I/O in high-Z). The device maintains full functionality across its specified ±10% V_CC range and guarantees t_ACC ≤ 70 ns under industrial conditions.

Key Specifications

Pinout & Package

DS1225AD-70 uses a JEDEC-standard 28-pin encapsulated DIP package (720-mil width, outline 21-0245), with lead-free RoHS-compliant finish denoted by the "+" suffix.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS1225Y-70IND+ and STK12C68-70I, the DS1225AD-70 uniquely combines industrial temperature operation, ±10% V_CC tolerance, UL-recognized lithium backup, and guaranteed 10-year retention-making it the sole choice for long-lifecycle, unattended industrial deployments.

Availability

DS1225AD-70 is available at Aetrix Electronics and suitable for industrial data loggers, smart energy meters, legacy PLC retrofits, and avionics configuration modules requiring stable component supply over 15+ year product lifecycles.

Supply support for DS1225AD-70 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) is a U.S.-based semiconductor company specializing in precision analog, mixed-signal, and power management ICs for industrial, automotive, and communications markets.

The DS1225AD-70 belongs to Maxim's legacy nonvolatile SRAM product line, engineered specifically for mission-critical memory retention in infrastructure equipment where firmware integrity and data survivability under power disruption are non-negotiable.

FAQ

What is the guaranteed data retention period for DS1225AD-70?

The DS1225AD-70 guarantees a minimum 10-year data retention period in the absence of external power, measured from the time V_CC is first applied and the internal lithium cell is activated. This specification is design-guaranteed per Maxim's reliability testing and documented in the datasheet revision 11/10, Note 9. The DS1225AD-70 achieves this via hermetically sealed lithium chemistry and automatic power-switching circuitry that isolates the battery until initial power-up.

Does DS1225AD-70 require external circuitry for battery backup operation?

No, the DS1225AD-70 requires no external circuitry for battery backup operation. Its integrated lithium energy source and power-fail detection circuitry automatically manage switching between V_CC and battery power. When V_CC drops below ~4.25 V, write protection engages; below ~3.0 V, the lithium cell powers the SRAM array. The DS1225AD-70 is fully self-contained and designed for direct replacement of volatile SRAMs without layout changes.

Is DS1225AD-70 pin-compatible with standard EPROMs and EEPROMs?

Yes, the DS1225AD-70 is pin-compatible with the 2764 EPROM and 2864 EEPROM, sharing identical 28-pin DIP pinout and byte-wide addressing. This allows direct substitution in existing designs without PCB modification. The DS1225AD-70 maintains the same A0–A12, DQ0–DQ7, CE, OE, and WE signal assignments, enabling seamless integration into legacy microprocessor systems originally designed for those EPROM/EEPROM families.

What is the write protection voltage threshold for DS1225AD-70?

DS1225AD-70 triggers unconditional write protection when V_CC falls within the range of 4.25 V to 4.5 V (V_TP), as specified in the DC Electrical Characteristics table. This threshold is lower than the DS1225AB's 4.5–4.75 V range, allowing earlier safeguard activation under marginal supply conditions. The DS1225AD-70's ±10% V_CC tolerance (4.5–5.5 V) ensures reliable operation across wider input variations while maintaining robust data integrity.

Can DS1225AD-70 operate in industrial temperature environments?

Yes, the DS1225AD-70IND+ variant is fully qualified for industrial temperature operation from –40°C to +85°C, as confirmed in the Ordering Information table and Absolute Maximum Ratings section. It undergoes extended burn-in and characterization across this range, supporting applications such as outdoor utility meters, factory automation controllers, and transportation electronics. The DS1225AD-70's CMOS design and lithium thermal stability ensure consistent 70 ns access time and data retention performance across the full industrial range.