AT27C256R-55RI Equivalent & Substitute Parts

Part Overview

The AT27C256R-55RI is a 256Kbit EPROM (Erasable Programmable Read-Only Memory) manufactured by Microchip Technology, configured as a 32K x 8 parallel memory device with 55 ns access time in a 28-SOIC surface mount package. This part is classified as obsolete, making substitute components necessary for new designs and ongoing system support. The device operates across the industrial temperature range of -40°C to 85°C with a 4.5V to 5.5V supply voltage.

Substiute Parts

AT27C256R-55RI

Microchip TechnologyIn Stock: 850AT27C256R-55RI Datasheet

Current PartRFQ

AT27C256R-70PU

Microchip TechnologyIn Stock: 6959AT27C256R-70PU Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution for the AT27C256R-55RI is determined by the following critical parameters:

• Memory capacity (256Kbit) and organization (32K x 8)
• Parallel memory interface
• Supply voltage range (4.5V ~ 5.5V)
• Operating temperature range (-40°C ~ 85°C)
• EPROM technology (OTP - One-Time Programmable)

The AT27C256R-70PU qualifies as a functional substitute based on matching memory size, organization, interface type, voltage specifications, and temperature range. The primary difference is the access time (70 ns versus 55 ns) and package format (28-DIP through-hole versus 28-SOIC surface mount).

Parameter Comparison

Engineering Selection Recommendations

The AT27C256R-70PU is an active product with ROHS3 compliance and unlimited moisture sensitivity level rating, providing superior long-term availability and environmental compliance compared to the obsolete AT27C256R-55RI. The 70 ns access time of the substitute is slower than the original 55 ns specification; selection of this substitute is appropriate only when system timing margins accommodate the additional 15 ns access delay.

Package format differs between the main part (28-SOIC surface mount) and substitute (28-DIP through-hole), requiring PCB layout and assembly process modifications. Both devices share identical memory capacity, organization, parallel interface, voltage supply range, and operating temperature specifications.

Frequently Asked Questions (FAQ)

Q: Can the AT27C256R-70PU directly replace the AT27C256R-55RI in existing designs?

A: Functional replacement is possible if system timing allows for the 70 ns access time versus the original 55 ns specification. Package format differs (28-DIP through-hole versus 28-SOIC surface mount), requiring PCB redesign and assembly process changes.

Q: What are the critical parameters for EPROM substitution?

A: Memory capacity (256Kbit), organization (32K x 8), parallel interface, supply voltage (4.5V ~ 5.5V), and operating temperature range (-40°C ~ 85°C) must match. Access time and package format are secondary considerations dependent on application requirements.

Q: Why is the AT27C256R-55RI classified as obsolete?

A: The part is no longer in active production. The AT27C256R-70PU remains in active production status and is the recommended alternative for new designs and system support.

Q: Are there compliance differences between these parts?

A: The AT27C256R-70PU is ROHS3 compliant with MSL rating of 1 (unlimited shelf life), while the AT27C256R-55RI is RoHS non-compliant with MSL rating of 2 (1 year shelf life). The substitute offers superior environmental compliance and storage stability.

Q: What is the impact of the 15 ns access time difference?

A: The AT27C256R-70PU has 70 ns access time compared to 55 ns for the original part. This difference is acceptable only in applications where system timing margins accommodate the slower access time. Critical timing-dependent circuits may require design review.