Microchip Technology AT28C040-25LI

Overview

AT28C040-25LI from Atmel is a 4-Mbit (512K × 8) paged parallel EEPROM with JEDEC-standard byte-wide pinout, 250 ns read access time, and industrial temperature range (–40°C to +85°C), housed in a 44-pad ceramic LCC package. It supports automatic page write of up to 256 bytes, hardware/software data protection, and DATA polling for write completion detection - used in firmware storage, configuration retention, and boot code backup in embedded controllers.

For engineers reviewing the AT28C040-25LI datasheet, AT28C040-25LI pinout, AT28C040-25LI application, or AT28C040-25LI equivalent, key selection considerations include its 5V ±10% single-supply operation, 10,000-cycle endurance, 10-year data retention, CMOS/TTL compatibility, and LCC-44 packaging for high-reliability industrial systems.

Technical Context

The AT28C040-25LI implements a paged write architecture with an internal 256-byte latch and self-timed programming using an on-chip control timer. Its dual-line chip enable (CE) and output enable (OE) logic enables bus contention avoidance in shared-memory systems.

It features both DATA polling (I/O7 complement toggle) and toggle-bit (I/O6 oscillation) methods for asynchronous write cycle completion detection, plus VCC sense and noise filtering to prevent inadvertent writes during power transitions or EMI events.

Key Specifications

Pinout & Package

AT28C040-25LI is packaged in a 44-pad ceramic leadless chip carrier (LCC), non-windowed, MIL-STD-1835 C-5 compliant, with side-brazed construction for hermetic sealing and thermal stability in harsh environments.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar paged parallel EEPROM applications.

Compared with ST M48T02-200PC1 and Microchip 25LC512-I/P, the AT28C040-25LI delivers 8× higher density, parallel bus speed, integrated page write acceleration, and industrial-qualified LCC packaging - making it optimal for legacy 8-bit microcontroller systems needing robust, high-capacity, pin-compatible nonvolatile memory.

Availability

AT28C040-25LI is available at Aetrix Electronics and suitable for industrial PLCs, medical diagnostics equipment, telecom base stations, and avionics subsystems requiring stable component supply, long-lifecycle support, and hermetically sealed memory solutions.

Supply support for AT28C040-25LI 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

Atmel Corporation (now part of Microchip Technology) is a fabless semiconductor company specializing in microcontrollers, nonvolatile memory, and secure authentication ICs for industrial, automotive, and communications markets.

The AT28C040 product line was designed for high-reliability, pin-compatible replacement of UV-erasable EPROMs and battery-backed SRAMs in legacy 5V embedded systems - emphasizing endurance, data retention, and JEDEC-compliant interoperability.

FAQ

What is the maximum page write size supported by the AT28C040-25LI?

The AT28C040-25LI supports page write operations of 1 to 256 bytes per cycle. All bytes written within a single page write must reside on the same 256-byte page, defined by address bits A8–A18. The internal latch holds the entire page, enabling the host processor to release the bus after initial address/data setup - a key efficiency advantage over byte-by-byte programming. This behavior is confirmed in the "Page Write" section of the AT28C040-25LI datasheet.

Does the AT28C040-25LI require a 12V programming voltage?

No, the AT28C040-25LI operates from a single 5V ±10% supply for both read and write operations. The 12V requirement applies only to the optional device identification area (7FF80H–7FFFFH), which is separate from main memory and not used in standard operation. All normal read/write functions - including page write, DATA polling, and software data protection - function fully at 5V. This eliminates need for charge pumps or external high-voltage generators.

How does hardware data protection work on the AT28C040-25LI?

The AT28C040-25LI implements four hardware safeguards: (1) VCC sense circuitry disables writes if supply drops below ~3.8V; (2) a 5 ms internal power-on delay prevents writes until stable operation is confirmed; (3) write inhibition occurs if CE is high, OE is low, or WE is high; and (4) input noise filters reject pulses shorter than 15 ns on CE/WE. These features collectively prevent corruption during power-up, brown-out, or EMI events - verified in the "Hardware Protection" subsection of the AT28C040-25LI datasheet.

Can the AT28C040-25LI be used as a direct replacement for standard SRAMs?

The AT28C040-25LI is pin- and function-compatible with 512K×8 SRAMs in read mode (CE/OE/WE control, I/O bidirectionality), but differs critically in write behavior: it requires self-timed programming and supports only page/byte writes, not true random-write. While it fits the same JEDEC socket and shares address/data bus timing, system firmware must implement DATA polling or toggle-bit checking to manage write completion - unlike SRAM's immediate write acknowledgment.

What is the purpose of the extra 256-byte device identification area in the AT28C040-25LI?

The AT28C040-25LI includes a dedicated 256-byte sector (addresses 7FF80H–7FFFFH) accessible only when A9 is raised to 12V ±0.5V. This area is intended for storing unique device identifiers, calibration constants, manufacturing lot codes, or firmware version stamps - physically isolated from main memory to prevent accidental overwrite during routine updates. Its use requires a temporary high-voltage signal but otherwise follows standard read/write protocols.