74F521SCX 8-Bit Identity Comparator Equivalent & Substitute Parts

Part Overview

The 74F521SCX is an 8-bit magnitude comparator with active low output manufactured by onsemi. This logic component performs identity comparison operations, outputting an active low A=B signal. The part is currently classified as obsolete, making equivalent and substitute parts necessary for ongoing design support and procurement.

Key Parameters

Parameter	Specification
Part Number	74F521SCX
Manufacturer	onsemi
Type	Identity Comparator
Number of Bits	8
Output Logic	Active Low
Output Function	A=B
Supply Voltage	4.5V ~ 5.5V
Output Current (High/Low)	1mA / 20mA
Max Propagation Delay	10ns @ 5V, 50pF
Operating Temperature	0°C ~ 70°C
Package	20-SOIC (0.295", 7.50mm Width)
Mounting Type	Surface Mount
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitution for the 74F521SCX is determined by strict equivalence across the following critical parameters:

8-bit identity comparator function
Active low output with A=B logic
Supply voltage range: 4.5V ~ 5.5V
Output current specifications: 1mA high, 20mA low
Propagation delay: 10ns @ 5V, 50pF
Operating temperature: 0°C ~ 70°C
Surface mount technology

Substitute parts are categorized as direct equivalents (identical electrical and mechanical specifications) or similar parts (functionally equivalent with minor package variations). All listed substitutes maintain full functional compatibility with the original 74F521SCX design.

Parameter Comparison

Parameter	74F521SCX (onsemi)	SN74F521DW (TI)	SN74F521DWR (TI)	SN74F521NSR (TI)
Type	Identity Comparator	Identity Comparator	Identity Comparator	Identity Comparator
Number of Bits	8	8	8	8
Output Logic	Active Low	Active Low	Active Low	Active Low
Output Function	A=B	A=B	A=B	A=B
Supply Voltage	4.5V ~ 5.5V	4.5V ~ 5.5V	4.5V ~ 5.5V	4.5V ~ 5.5V
Output Current (High/Low)	1mA / 20mA	1mA / 20mA	1mA / 20mA	1mA / 20mA
Max Propagation Delay	10ns @ 5V, 50pF	10ns @ 5V, 50pF	10ns @ 5V, 50pF	10ns @ 5V, 50pF
Operating Temperature	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C
Package / Case	20-SOIC (0.295", 7.50mm)	20-SOIC (0.295", 7.50mm)	20-SOIC (0.295", 7.50mm)	20-SOIC (0.209", 5.30mm)
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount
Product Status	Obsolete	Last Time Buy	Active	Active
RoHS Status	Not specified	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

For designs currently using the 74F521SCX, the following selection criteria apply based on product status and compliance:

SN74F521DWR (Texas Instruments) is the primary recommended substitute. This part maintains active product status, offers ROHS3 compliance, and is available in cut tape and digi-reel packaging formats. The electrical and mechanical specifications are identical to the original 74F521SCX, ensuring direct functional replacement.

SN74F521DW (Texas Instruments) serves as an alternative direct substitute with identical specifications. This part carries last time buy status, indicating limited future availability. Selection of this part should account for long-term supply considerations.

SN74F521NSR (Texas Instruments) is functionally equivalent but features a narrower 20-SO package (0.209" width versus 0.295" width). This part is actively produced and ROHS3 compliant. Package width difference requires PCB layout verification before implementation.

All three Texas Instruments substitutes provide ROHS3 compliance and REACH unaffected status, meeting modern environmental and regulatory requirements.

Frequently Asked Questions (FAQ)

Q: Can SN74F521DWR directly replace 74F521SCX without PCB modifications?

A: Yes. The SN74F521DWR maintains identical electrical specifications and 20-SOIC package dimensions (0.295", 7.50mm width), enabling direct pin-compatible replacement without PCB layout changes.

Q: What is the difference between SN74F521DW and SN74F521DWR?

A: Both parts are electrically identical 8-bit identity comparators with active low output. The primary difference is packaging format: SN74F521DW is supplied in tube packaging, while SN74F521DWR is supplied in cut tape and digi-reel formats. SN74F521DWR carries active product status; SN74F521DW is last time buy.

Q: Can SN74F521NSR be used as a substitute?

A: SN74F521NSR is functionally equivalent with identical electrical performance. However, the package width differs (0.209" versus 0.295"), requiring PCB footprint verification. The narrower package may not be compatible with existing board layouts designed for the standard 0.295" width.

Q: Are all substitutes ROHS3 compliant?

A: Yes. SN74F521DW, SN74F521DWR, and SN74F521NSR are all ROHS3 compliant and REACH unaffected, meeting current environmental regulations.

Q: What is the propagation delay specification for these comparators?

A: All listed parts, including the original 74F521SCX, specify a maximum propagation delay of 10 nanoseconds at 5V supply voltage with 50pF load capacitance.

Q: Are there any supply voltage or temperature range differences between substitutes?

A: No. All parts operate across the identical supply voltage range (4.5V ~ 5.5V) and temperature range (0°C ~ 70°C), ensuring functional compatibility in existing circuit designs.

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