AT27C256R-90JC Equivalent & Substitute Parts

Part Overview

The AT27C256R-90JC is a 256Kbit parallel EPROM (Erasable Programmable Read-Only Memory) manufactured by Microchip Technology in a 32-PLCC surface mount package. This part is classified as obsolete, which necessitates identification of functionally equivalent alternatives for ongoing system support and new designs. The 90 ns access time and 4.5V to 5.5V supply voltage define its operational characteristics within legacy embedded systems and industrial applications.

Key Parameters

Parameter	Value
Memory Type	Non-Volatile EPROM
Memory Size	256Kbit
Memory Organization	32K x 8
Memory Interface	Parallel
Access Time	90 ns
Voltage Supply	4.5V ~ 5.5V
Package Type	32-PLCC (13.97x11.43)
Mounting Type	Surface Mount
Operating Temperature	0°C ~ 70°C
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution of the AT27C256R-90JC is determined by the following critical parameters:

Memory Capacity & Organization: Must be 256Kbit with 32K x 8 organization to maintain address and data bus compatibility
Memory Interface: Must be parallel interface to ensure pin-level compatibility
Package & Pinout: Must use 32-PLCC (13.97x11.43) surface mount package to fit existing PCB layouts
Voltage Supply Range: Must operate within 4.5V to 5.5V to match power distribution architecture
Access Time: Substitute parts with equal or faster access time (≤90 ns) maintain or improve system timing margins

The AT27C256R-70JU qualifies as a direct substitute based on these parameters. It maintains identical memory capacity, organization, interface type, and package specification while offering improved access time (70 ns versus 90 ns) and extended operating temperature range.

Parameter Comparison

Parameter	AT27C256R-90JC (Main Part)	AT27C256R-70JU (Substitute)
Manufacturer	Microchip Technology	Microchip Technology
Memory Type	Non-Volatile EPROM	Non-Volatile EPROM
Memory Size	256Kbit	256Kbit
Memory Organization	32K x 8	32K x 8
Memory Interface	Parallel	Parallel
Access Time	90 ns	70 ns
Voltage Supply	4.5V ~ 5.5V	4.5V ~ 5.5V
Package Type	32-PLCC (13.97x11.43)	32-PLCC (13.97x11.43)
Mounting Type	Surface Mount	Surface Mount
Operating Temperature	0°C ~ 70°C	-40°C ~ 85°C
Product Status	Obsolete	Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant

Engineering Selection Recommendations

The AT27C256R-70JU is the qualified substitute for the AT27C256R-90JC based on the following engineering criteria:

Functional Compatibility: Both parts share identical memory capacity (256Kbit), organization (32K x 8), parallel interface, and 32-PLCC package specification. Pin-for-pin compatibility is maintained, enabling direct PCB substitution without layout modifications.

Performance Advantage: The substitute part provides faster access time (70 ns versus 90 ns), which improves system timing margins and is backward-compatible with designs specified for 90 ns operation.

Product Status & Availability: The AT27C256R-70JU maintains active product status with verified availability, whereas the main part is obsolete. This ensures long-term supply chain viability for production and field replacement scenarios.

Compliance Posture: The substitute part achieves ROHS3 compliance and REACH unaffected status, aligning with modern regulatory requirements. The main part is RoHS non-compliant, making the substitute preferable for new designs and regulated applications.

Temperature Range Extension: The substitute operates across -40°C to 85°C, providing broader environmental coverage compared to the main part's 0°C to 70°C range, suitable for extended industrial and automotive applications.

Frequently Asked Questions (FAQ)

Q: Can the AT27C256R-70JU be used as a direct replacement for the AT27C256R-90JC?

A: Yes. Both parts are pin-for-pin compatible with identical 32-PLCC packaging, memory capacity (256Kbit), organization (32K x 8), parallel interface, and supply voltage range (4.5V ~ 5.5V). No PCB modifications are required.

Q: What is the difference in access time between these parts?

A: The AT27C256R-90JC has 90 ns access time, while the AT27C256R-70JU has 70 ns access time. The faster access time of the substitute part improves system timing performance and is fully compatible with designs specified for 90 ns operation.

Q: Are there packaging differences between these parts?

A: No. Both parts use the 32-PLCC (13.97x11.43) surface mount package with identical pinout and footprint specifications.

Q: Why is the main part listed as obsolete?

A: The AT27C256R-90JC is classified as obsolete by the manufacturer. The AT27C256R-70JU remains in active production, making it the recommended choice for new designs and ongoing system support.

Q: Does the substitute part meet modern compliance standards?

A: Yes. The AT27C256R-70JU is ROHS3 compliant and REACH unaffected, whereas the main part is RoHS non-compliant. This makes the substitute suitable for applications requiring regulatory compliance.

Q: What is the operating temperature range difference?

A: The AT27C256R-90JC operates from 0°C to 70°C, while the AT27C256R-70JU operates from -40°C to 85°C. The extended range of the substitute part accommodates broader environmental conditions in industrial and automotive applications.

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