Microchip Technology AT28C040-25BI

Overview

AT28C040-25BI from Atmel is a 4-Mbit (512K × 8) paged parallel EEPROM with JEDEC-standard byte-wide pinout, 250 ns read access time, and 10 ms maximum page write cycle time. It operates on single 5V ±10% supply, supports hardware/software data protection, and is rated for industrial temperature range (–40°C to +85°C), commonly used in firmware storage and configuration retention for embedded controllers.

For engineers reviewing the AT28C040-25BI datasheet, AT28C040-25BI pinout, AT28C040-25BI application, or AT28C040-25BI equivalent, key selection considerations include its 256-byte page write capability, DATA polling and toggle-bit write completion detection, CMOS/TTL compatibility, and industrial-grade reliability with 10,000 write cycles and 10-year data retention.

Technical Context

The AT28C040-25BI implements a static RAM-like read interface with dual-line chip enable (CE) and output enable (OE) control, enabling bus contention avoidance. Its internal 256-byte page register latches address and data during write operations, decoupling the host bus after initiation.

Write execution uses an internal control timer; completion is signaled via DATA polling on I/O7 or toggle-bit behavior on I/O6. Hardware protection includes VCC sense (<3.8 V inhibit), 5 ms power-on delay, and noise filtering on WE/CE inputs; software protection uses a 3-byte command sequence to enable/disable write lock.

Key Specifications

Pinout & Package

Ceramic Leadless Chip Carrier (LCC), 44-pad, non-windowed, MIL-STD-1835 C-5 compliant package with side-braze construction and flat top surface. Pin #1 identified by corner cut and dot marking.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ST M48T02-200PC1 and Microchip 25LC512-I/P, the AT28C040-25BI delivers 8× higher density with deterministic parallel bus timing, integrated page write acceleration, and dual-layer (hardware + software) write protection-making it optimal for legacy industrial systems requiring high-reliability, high-throughput firmware storage without redesigning the memory interface.

Availability

AT28C040-25BI is available at Aetrix Electronics and suitable for industrial PLCs, telecom line cards, automotive body control modules, medical diagnostic equipment, and legacy embedded systems requiring stable component supply and long-term obsolescence management.

Supply support for AT28C040-25BI 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.

The AT28C040-25BI belongs to Atmel's parallel EEPROM product line, designed specifically for high-reliability, pin-compatible replacement of EPROM and battery-backed SRAM in legacy industrial and telecom systems requiring fast, page-based reprogrammability.

FAQ

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

The AT28C040-25BI supports a maximum page write size of 256 bytes. This is enabled by its internal 256-byte page register, which latches address and data on the first write pulse and allows up to 255 additional bytes within 150 µs of each prior byte. The AT28C040-25BI requires all bytes in a page write to reside on the same page, defined by A8–A18 inputs remaining constant throughout the operation.

How does the AT28C040-25BI indicate write completion without using external timers?

The AT28C040-25BI provides two hardware-confirmed methods: DATA polling on I/O7 (returns complement of written data until complete, then true data) and toggle-bit detection on I/O6 (toggles between 0 and 1 during write, stabilizes when done). Both methods allow the host to poll asynchronously-no fixed delays or external timing components are needed. These mechanisms are fully functional for both byte and page writes in the AT28C040-25BI.

Does the AT28C040-25BI require a 12V supply for any operation?

The AT28C040-25BI operates entirely from a single 5V ±10% supply during normal read/write operations. A 12V ±0.5V supply on pin A9 is required only for accessing the dedicated 256-byte device identification area (7FF80H–7FFFFH); this is optional and not needed for standard memory functions. All other features-including software data protection, page write, and hardware write inhibit-function at 5V. The AT28C040-25BI does not use 12V for programming or erase.

What is the purpose of the NC pins on the AT28C040-25BI LCC package?

The NC (No Connect) pins on the AT28C040-25BI's 44-pad LCC package-such as pins 11–13, 16–19, 26–28, and 36–39-are physically present but electrically unbonded and isolated from internal circuitry. They must remain unconnected (floating) on the PCB; routing traces or applying voltage to these pins may cause latch-up or damage. Their presence accommodates package standardization and die layout constraints, not functional expansion. This applies strictly to the AT28C040-25BI in 44L packaging.

Can the AT28C040-25BI be used as a direct replacement for older EPROMs like the 27C040?

No-the AT28C040-25BI is not a pin-compatible or functionally drop-in replacement for UV-erasable EPROMs such as the 27C040. While both are 4 Mbit ×8 parallel devices with similar pin counts, the AT28C040-25BI requires active WE control, supports page writes and software protection, and has different timing (e.g., tWP = 100 ns vs. EPROM's longer write pulse), CE/OE logic, and no UV window. Direct substitution would require firmware and timing adjustments. The AT28C040-25BI is intended as an upgrade path-not a mechanical swap-for systems migrating from EPROM to electrically erasable memory.