Analog Devices Inc./Maxim Integrated DS1225AB-85+

Overview

DS1225AB-85+ from Maxim Integrated is a 64k-bit (8k × 8) nonvolatile static RAM with integrated lithium battery backup, JEDEC-standard 28-pin extended DIP package, 70 ns access time, ±5% V_CC tolerance (4.75–5.25 V), and industrial temperature range (–40°C to +85°C). It replaces volatile SRAMs and EEPROMs in embedded controllers requiring persistent data retention during power loss.

For engineers reviewing the DS1225AB-85+ datasheet, DS1225AB-85+ pinout, DS1225AB-85+ application, or DS1225AB-85+ equivalent, key selection factors include automatic write protection at 4.5 V, unlimited write cycles, 10-year data retention without external power, and direct pin compatibility with 2764 EPROM and 2864 EEPROM sockets.

Technical Context

The DS1225AB-85+ integrates a self-contained lithium energy source and voltage-monitoring circuitry that autonomously switches to battery backup when V_CC falls below 4.5 V, enabling seamless data retention. Its control logic enforces unconditional write protection and high-impedance outputs during power failure, eliminating need for external supervision circuitry.

It operates as a byte-wide parallel memory with full static CMOS interface timing: t_ACC = 70 ns, t_RC = 70 ns, t_WP = 55 ns, and supports standard microprocessor bus protocols via CE, WE, and OE controls - all compliant with JEDEC 28-pin DIP mechanical and signal definitions.

Key Specifications

Pinout & Package

DS1225AB-85+ uses a JEDEC-standard 28-pin extended dual in-line package (EDIP), 720 mil width, with through-hole mounting and wave/hand soldering compatibility. Pin 1 is marked with dot or notch; NC pins are electrically isolated and must remain unconnected.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS1225AD-85+, the DS1225AB-85+ offers higher write-protection voltage (4.5 V vs. 4.25 V), improving noise immunity in noisy industrial environments; versus STK12C68-E25I, it delivers double the data retention (10 vs. 5 years) without external charge management circuitry.

Availability

DS1225AB-85+ is available at Aetrix Electronics and suitable for industrial data loggers, utility metering systems, and medical device configuration storage requiring stable component supply, long-term lifecycle support, and RoHS-compliant through-hole memory solutions.

Supply support for DS1225AB-85+ 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, medical, and communications markets.

The DS1225AB-85+ belongs to Maxim's nonvolatile SRAM product line, designed specifically to replace aging EPROM, EEPROM, and battery-backed SRAM in legacy systems requiring zero-footprint, pin-compatible, maintenance-free data retention.

FAQ

What is the guaranteed data retention period for DS1225AB-85+?

The DS1225AB-85+ 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 value is design-guaranteed and based on accelerated life testing per Maxim's reliability qualification standards - not extrapolated or estimated.

Does DS1225AB-85+ require external circuitry for battery backup management?

No, the DS1225AB-85+ contains fully integrated lithium battery backup with automatic switchover circuitry. No external capacitors, charge pumps, or supervisory ICs are needed. The lithium cell remains disconnected until first power-up, ensuring full capacity at installation - a feature unique to the DS1225AB-85+ among nonvolatile SRAMs.

Is DS1225AB-85+ pin-compatible with standard 2764 EPROMs?

Yes, the DS1225AB-85+ uses identical 28-pin extended DIP pinout and timing as the 2764 EPROM, including matching A0–A12, DQ0–DQ7, CE, OE, and WE assignments. This allows direct socket replacement in legacy designs without PCB modification or firmware changes.

What is the write protection voltage threshold for DS1225AB-85+?

The DS1225AB-85+ asserts hardware write protection when V_CC falls below 4.50 V (minimum), with typical activation at 4.62 V and maximum at 4.75 V. This threshold is tighter than the DS1225AD variant and provides enhanced immunity against false triggers in electrically noisy industrial environments.

Can DS1225AB-85+ operate at temperatures down to –40°C?

Yes, the DS1225AB-85+ is rated for industrial temperature operation from –40°C to +85°C, as indicated by the "IND" suffix in its ordering code. All DC and AC specifications, including 70 ns access time and write pulse width, are guaranteed across this full range - validated per JEDEC JESD22-A108 thermal cycling standards.