AT27C256R-45RC Equivalent & Substitute Parts

Part Overview

The AT27C256R-45RC is a 256Kbit EPROM (Erasable Programmable Read-Only Memory) manufactured by Microchip Technology, packaged in 28-SOIC surface mount configuration with 45 ns access time. This part is classified as obsolete, indicating it has been discontinued and is no longer in active production. Finding equivalent or substitute parts is necessary due to limited availability and the transition to active product lines that maintain ongoing manufacturing support and compliance certifications.

Substiute Parts

AT27C256R-45RC

Microchip TechnologyIn Stock: 985AT27C256R-45RC Datasheet

Current PartRFQ

AT27C256R-70PU

Microchip TechnologyIn Stock: 6959AT27C256R-70PU Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution for the AT27C256R-45RC is determined by the following core electrical and mechanical parameters:

Electrical Compatibility Requirements:

• Memory capacity: 256Kbit (32K x 8 organization)
• Memory interface: Parallel
• Voltage supply range: 4.5V ~ 5.5V
• Memory technology: EPROM - OTP (One-Time Programmable)

Mechanical Compatibility Considerations:

• Package type and pin count must match or be pin-compatible
• Mounting type (surface mount vs. through-hole) affects PCB integration

Performance Parameters:

• Access time tolerance: Substitute parts with equal or faster access time maintain functional compatibility
• Operating temperature range: Substitute parts with equal or wider temperature range ensure operational reliability

The AT27C256R-70PU qualifies as a substitute based on matching electrical specifications (256Kbit capacity, parallel interface, 4.5V ~ 5.5V supply) and identical memory organization. However, packaging differs (28-DIP through-hole vs. 28-SOIC surface mount), requiring PCB redesign considerations.

Parameter Comparison

Engineering Selection Recommendations

Product Status Consideration: The AT27C256R-70PU is classified as active, ensuring ongoing manufacturing availability and supply chain reliability compared to the obsolete AT27C256R-45RC. This status difference is significant for long-term production and support requirements.

Compliance Certification: The AT27C256R-70PU carries ROHS3 compliance certification, whereas the main part is RoHS non-compliant. For applications subject to RoHS regulations or customer requirements, the substitute part provides regulatory alignment.

Electrical Functionality: Both parts share identical memory capacity, organization, interface type, and supply voltage specifications. The AT27C256R-70PU operates across a wider temperature range (-40°C ~ 85°C vs. 0°C ~ 70°C), providing extended environmental tolerance.

Access Time Trade-off: The substitute part specifies 70 ns access time compared to 45 ns for the main part. This represents a 55% increase in access latency. Substitution is valid only if system timing requirements accommodate the slower access time.

Packaging Impact: The transition from 28-SOIC surface mount to 28-DIP through-hole packaging requires PCB redesign and assembly process modification. Pin compatibility exists, but physical footprint and mounting methodology differ fundamentally.

Frequently Asked Questions (FAQ)

Q: Can AT27C256R-70PU directly replace AT27C256R-45RC on the same PCB?

A: No. The AT27C256R-45RC uses 28-SOIC surface mount packaging, while the AT27C256R-70PU uses 28-DIP through-hole packaging. Although pin counts and electrical specifications are compatible, the physical footprints are incompatible. PCB redesign is required.

Q: Does the 70 ns access time of the substitute part affect system performance?

A: Access time impact depends on system timing specifications. The AT27C256R-70PU has 25 ns slower access time than the main part. If the original design includes timing margins or if system clock frequencies are low enough to accommodate 70 ns latency, functional compatibility is maintained. If timing is critical, verify that system timing budgets can absorb this difference.

Q: Why is the AT27C256R-45RC obsolete?

A: The AT27C256R-45RC is classified as obsolete, indicating Microchip Technology has discontinued manufacturing. Obsolete status typically reflects market transition to newer memory technologies or product line consolidation. The AT27C256R-70PU remains in active production.

Q: Are there electrical differences between the two parts?

A: Both parts share identical memory capacity (256Kbit), organization (32K x 8), interface type (parallel), and supply voltage range (4.5V ~ 5.5V). The AT27C256R-70PU operates across a wider temperature range (-40°C ~ 85°C vs. 0°C ~ 70°C), providing extended environmental tolerance.

Q: What is the significance of RoHS compliance difference?

A: The AT27C256R-45RC is RoHS non-compliant, while the AT27C256R-70PU is ROHS3 compliant. RoHS compliance restricts hazardous substances in electrical and electronic equipment. For applications subject to RoHS regulations or customer requirements, the substitute part provides regulatory alignment.

Q: Can I use the AT27C256R-70PU in a new design instead of the obsolete part?

A: Yes, provided PCB layout accommodates 28-DIP through-hole packaging and system timing requirements accept 70 ns access time. The active product status and RoHS3 compliance make the AT27C256R-70PU suitable for new designs requiring 256Kbit parallel EPROM functionality.