Microchip Technology AT28BV256-20JU-T

Overview

AT28BV256-20JU-T from Atmel is a 256 Kbit (32K × 8) parallel EEPROM with JEDEC-standard byte-wide pinout, operating from 2.7V–3.6V, featuring 200 ns read access time, 10 ms max page write cycle, 15 mA active current, and industrial temperature range (−40°C to +85°C). It supports hardware/software data protection and is used in embedded systems requiring nonvolatile storage for configuration, calibration, or firmware patch storage.

For engineers reviewing the AT28BV256-20JU-T datasheet, AT28BV256-20JU-T pinout, AT28BV256-20JU-T application, or AT28BV256-20JU-T equivalent, key selection criteria include voltage compatibility (2.7–3.6 V), PLCC-32 package constraints, page-write timing (≤10 ms), Data Polling/Toggle Bit write completion detection, and software data protection enablement sequence.

Technical Context

The AT28BV256-20JU-T implements a parallel interface with CE/OE/WE control logic enabling SRAM-like read/write access without external timing components. Its internal 64-byte page register latches up to 64 bytes per write cycle, with address/data capture on falling CE or WE edges and automatic internal programming via an integrated timer.

Write completion is verified via dual methods: Data Polling (I/O7 complement-to-data toggle) and Toggle Bit (I/O6 toggling during write, stable after completion). Software Data Protection requires a three-byte unlock sequence (5555H/2AAAH/5555H) before any write, preventing inadvertent writes during power transitions.

Key Specifications

Pinout & Package

AT28BV256-20JU-T uses a 32-lead Plastic Leaded Chip Carrier (PLCC) package with JEDEC-standard byte-wide pinout. Pins 1 and 17 are No Connect (NC). The package is Pb/halide-free and rated for industrial temperature range (−40°C to +85°C).

Key Features

Applications

Equivalent & Alternatives

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

Compared with ST M28W256FBD-20ZB6 and Microchip 25LC256-I/P, the AT28BV256-20JU-T uniquely combines 2.7–3.6 V operation, parallel JEDEC pinout, hardware/software write protection, and dual-status detection - making it the only drop-in solution for upgrading legacy 5 V systems to 3.3 V while preserving timing and security.

Availability

AT28BV256-20JU-T is available at Aetrix Electronics and suitable for industrial PLCs, medical diagnostics equipment, telecom base stations, and automotive ECUs requiring stable component supply with guaranteed long-term availability.

Supply support for AT28BV256-20JU-T 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 semiconductor manufacturer specializing in microcontrollers, nonvolatile memory, and secure authentication ICs.

The AT28BV256 belongs to Atmel's battery-voltage parallel EEPROM product line, designed for reliable, low-power nonvolatile storage in industrial, medical, and communications equipment where SRAM-like interface simplicity and robust data integrity are essential.

FAQ

What is the correct power-up sequence to avoid unintended writes on the AT28BV256-20JU-T?

The AT28BV256-20JU-T incorporates an internal VCC power-on delay of approximately 10 ms. To prevent unintended writes, ensure VCC rises cleanly to ≥2.7 V before asserting CE, OE, or WE signals. Hold CE high, OE high, and WE high during power ramp-up, and wait ≥10 ms after VCC stabilization before initiating any write commands. This hardware feature is active regardless of software data protection status and applies specifically to the AT28BV256-20JU-T's PLCC-32 package.

How does the software data protection (SDP) sequence work for the AT28BV256-20JU-T?

The AT28BV256-20JU-T requires a precise three-byte unlock sequence before any write: first write 0xAA to address 0x5555, then 0x55 to address 0x2AAA, then 0xA0 to address 0x5555. Only after this sequence is completed can byte or page writes proceed. Each subsequent write operation - even within the same page - must restart this sequence. The AT28BV256-20JU-T ignores data written without the full sequence but still consumes write-cycle time (tWC), so proper sequencing is mandatory for functional writes.

Can the AT28BV256-20JU-T be used as a direct replacement for older 5 V parallel EEPROMs like the AT28C256?

No, the AT28BV256-20JU-T is not a direct replacement for 5 V devices such as the AT28C256 due to its 2.7–3.6 V supply requirement and absence of 5 V tolerance on inputs. While pinout and command structure are JEDEC-compatible, applying 5 V to VCC or I/O pins will damage the AT28BV256-20JU-T. It is designed for 3.3 V systems; use only with level-shifters or in native 3.3 V designs. The AT28BV256-20JU-T's lower voltage operation enables reduced power consumption and battery compatibility absent in the AT28C256.

What is the maximum number of bytes that can be written in a single page write cycle on the AT28BV256-20JU-T?

The AT28BV256-20JU-T supports up to 64 bytes per page write cycle, constrained by its internal 64-byte page register. All bytes must reside on the same page, defined by address bits A6–A14; A0–A5 select byte positions within that page. Each successive byte must be loaded within 150 µs (tBLC) of the prior one. Exceeding this interval terminates the page load and starts internal programming. This capability is intrinsic to the AT28BV256-20JU-T's architecture and applies identically across all supported packages including the JU variant.

How do Data Polling and Toggle Bit mechanisms differ in detecting write completion on the AT28BV256-20JU-T?

Data Polling monitors I/O7: during a write, reading the last-written address returns the complement of the data until completion, then true data. Toggle Bit monitors I/O6: it toggles between 0 and 1 during the write and stabilizes upon completion. Both operate asynchronously and can be polled at any time. Data Polling requires reading the specific target address; Toggle Bit allows polling any fixed address. The AT28BV256-20JU-T supports both simultaneously, giving designers flexibility - e.g., using I/O7 for critical writes and I/O6 for background status checks without address dependency.