SN74HC688PWT Equivalent & Substitute Parts

Part Overview

The SN74HC688PWT is an 8-bit identity comparator manufactured by Texas Instruments, designed for magnitude comparison applications with active-low output. This device is currently discontinued at DiGi Electronics, making equivalent and substitute parts necessary for ongoing design support and procurement.

The SN74HC688PWT operates across a 2V to 6V supply range and delivers A=B output functionality in a 20-TSSOP surface-mount package. Its discontinuation status necessitates identification of functionally equivalent alternatives that maintain electrical and mechanical compatibility.

Key Parameters

Parameter	Value
Manufacturer Part Number	SN74HC688PWT
Manufacturer	Texas Instruments
Category	Logic
Type	Identity Comparator
Number of Bits	8
Output Function	A=B (Active Low)
Voltage - Supply	2V ~ 6V
Current - Output High, Low	5.2mA, 5.2mA
Max Propagation Delay @ 6V, 50pF	36ns
Current - Quiescent (Iq)	8 µA
Operating Temperature	-40°C ~ 85°C
Package / Case	20-TSSOP (0.173", 4.40mm Width)
Mounting Type	Surface Mount
RoHS Status	ROHS3 Compliant
Product Status	Discontinued at DiGi Electronics

Substitute Part Grouping Explanation

Substitution for the SN74HC688PWT is determined by strict alignment of the following electrical and mechanical parameters:

Primary Substitution Criteria:

Functional type: 8-bit identity comparator with A=B output
Output logic: Active low
Supply voltage range: 2V ~ 6V minimum compatibility
Package type: 20-TSSOP surface mount
Output current capability: 5.2mA minimum
Quiescent current: 8 µA maximum
RoHS3 compliance and MSL Level 1 rating

Direct Substitutes maintain identical electrical specifications and package configuration, enabling pin-for-pin replacement without circuit modification.

Manufacturer-Recommended Substitutes may exhibit improved performance characteristics (lower propagation delay, extended temperature range) while maintaining functional equivalence and package compatibility.

Parameter Comparison

Parameter	SN74HC688PWT (Main)	SN74HC688PWR (Direct)	74HC688PW,118 (MFR Recommended)
Manufacturer	Texas Instruments	Texas Instruments	Nexperia USA Inc.
Type	Identity Comparator	Identity Comparator	Identity Comparator
Number of Bits	8	8	8
Output Function	A=B (Active Low)	A=B (Active Low)	A=B (Active Low)
Voltage - Supply	2V ~ 6V	2V ~ 6V	2V ~ 6V
Current - Output High, Low	5.2mA, 5.2mA	5.2mA, 5.2mA	5.2mA, 5.2mA
Max Propagation Delay @ 6V, 50pF	36ns	36ns	29ns
Current - Quiescent (Iq)	8 µA	8 µA	8 µA
Operating Temperature	-40°C ~ 85°C	-40°C ~ 85°C	-40°C ~ 125°C
Package / Case	20-TSSOP	20-TSSOP	20-TSSOP
Packaging Format	Tape & Reel (TR)	Cut Tape (CT) & Digi-Reel®	Tape & Reel (TR)
Product Status	Discontinued at DiGi Electronics	Active	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

SN74HC688PWR (Direct Substitute): This Texas Instruments part maintains identical electrical specifications and package configuration to the SN74HC688PWT. The primary distinction is packaging format (Cut Tape & Digi-Reel versus Tape & Reel), which does not affect functional performance. This part is currently active in production and represents the most direct replacement path. Inventory availability is 1900 units.

74HC688PW,118 (Manufacturer-Recommended Substitute): Manufactured by Nexperia USA Inc., this part delivers improved propagation delay performance (29ns versus 36ns at 6V, 50pF) and extended operating temperature range (-40°C to 125°C versus -40°C to 85°C). All electrical parameters remain within or exceed the original specification envelope. This part is active in production with 3398 units available. The extended temperature range provides additional design margin for applications requiring operation beyond 85°C.

Both substitutes maintain ROHS3 compliance, MSL Level 1 rating, and identical pin configuration, enabling direct circuit board replacement without design modification.

Frequently Asked Questions (FAQ)

Q: Can SN74HC688PWR be used as a direct replacement for SN74HC688PWT?

A: Yes. Both parts are 8-bit identity comparators with identical electrical specifications, output function (A=B active low), supply voltage range (2V ~ 6V), output current (5.2mA), propagation delay (36ns @ 6V, 50pF), and 20-TSSOP package. The packaging format difference (Cut Tape & Digi-Reel versus Tape & Reel) does not affect functional performance or circuit compatibility.

Q: What are the advantages of 74HC688PW,118 over the original SN74HC688PWT?

A: The 74HC688PW,118 offers two performance improvements: reduced propagation delay (29ns versus 36ns at 6V, 50pF) and extended operating temperature range (-40°C to 125°C versus -40°C to 85°C). All other electrical parameters remain equivalent. These improvements provide additional design margin without requiring circuit modification.

Q: Are all three parts pin-compatible?

A: Yes. All three parts use the 20-TSSOP package with identical pin assignments. No PCB layout changes are required for substitution.

Q: What is the difference between Tape & Reel and Cut Tape packaging?

A: Both are surface-mount packaging formats suitable for automated assembly. Tape & Reel is continuous reel packaging for high-volume production. Cut Tape & Digi-Reel is pre-cut tape format for smaller quantity orders. Functional performance is identical.

Q: Do all substitute parts meet RoHS3 compliance?

A: Yes. SN74HC688PWR and 74HC688PW,118 are both ROHS3 compliant with MSL Level 1 rating, matching the original SN74HC688PWT specification.

Q: Which substitute should be selected for new designs?

A: Selection depends on application requirements. For standard applications within -40°C to 85°C operating range, SN74HC688PWR provides direct equivalence. For applications requiring extended temperature operation or improved timing performance, 74HC688PW,118 is the appropriate selection.

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