SN74ALS33AD Equivalent & Substitute Parts

Part Overview

The SN74ALS33AD is a 4-channel NOR gate logic IC with open collector outputs in a 14-SOIC surface mount package, manufactured by Texas Instruments. This part operates within the 4.5V to 5.5V supply voltage range and is classified as obsolete. Due to its obsolete status, equivalent substitute parts from active product lines are necessary to maintain design continuity and ensure long-term component availability for new production and field replacements.

Key Parameters

Parameter	Value
Logic Type	NOR Gate
Number of Circuits	4
Number of Inputs	2
Features	Open Collector
Package Type	14-SOIC (0.154", 3.90mm Width)
Mounting Type	Surface Mount
Operating Temperature Range	0°C ~ 70°C
Input Logic Level - Low	0.8V
Input Logic Level - High	2V
Output Current (Low)	24mA

Substitute Part Grouping Explanation

Substitution of the SN74ALS33AD is determined by the following critical parameters:

Logic Function: All substitute parts must implement a 4-channel, 2-input NOR gate with open collector output configuration
Package Compatibility: All substitutes must use the 14-SOIC surface mount package with identical pin assignments
Electrical Characteristics: Input logic levels (0.8V low, 2V high) and output current capability (24mA) must be maintained
Operating Temperature: All substitutes must support the 0°C to 70°C operating range
Supply Voltage Tolerance: While the main part specifies 4.5V ~ 5.5V, substitute parts operate within 4.75V ~ 5.25V, which is a subset of the original specification and therefore compatible

The identified substitutes belong to the 74LS logic family, which maintains functional and pin compatibility with the 74ALS series while offering active product status and improved availability.

Parameter Comparison

Parameter	SN74ALS33AD	SN74LS33D	SN74LS33DR
Manufacturer	Texas Instruments	onsemi	Texas Instruments
Series	74ALS	74LS	74LS
Product Status	Obsolete	Active	Active
Logic Type	NOR Gate	NOR Gate	NOR Gate
Number of Circuits	4	4	4
Number of Inputs	2	2	2
Features	Open Collector	Open Collector	Open Collector
Voltage - Supply	4.5V ~ 5.5V	4.75V ~ 5.25V	4.75V ~ 5.25V
Output Current (Low)	24mA	24mA	24mA
Input Logic Level - Low	0.8V	0.8V	0.8V
Input Logic Level - High	2V	2V	2V
Max Propagation Delay @ 5V	33ns @ 50pF	32ns @ 45pF	32ns @ 45pF
Operating Temperature	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C
Package / Case	14-SOIC (0.154", 3.90mm Width)	14-SOIC (0.154", 3.90mm Width)	14-SOIC (0.154", 3.90mm Width)
RoHS Status	ROHS3 Compliant	Not specified	ROHS3 Compliant
REACH Status	REACH Unaffected	Not specified	REACH Unaffected

Engineering Selection Recommendations

Both SN74LS33D and SN74LS33DR are functionally equivalent substitutes for the obsolete SN74ALS33AD. Selection between these options should be based on the following criteria:

SN74LS33DR (Texas Instruments, Tape & Reel packaging): This part maintains Texas Instruments as the original manufacturer and includes ROHS3 compliance and REACH unaffected status, matching the regulatory profile of the main part. The tape and reel packaging is suitable for automated assembly processes. Inventory availability is 874 units.

SN74LS33D (onsemi, Bulk packaging): This part offers significantly higher inventory availability at 65,780 units and maintains full functional compatibility. Bulk packaging is suitable for manual assembly or lower-volume applications. Regulatory compliance details are not specified in the provided data.

Both parts demonstrate improved propagation delay performance (32ns versus 33ns) and operate within compatible supply voltage ranges. The narrower supply voltage specification of the 74LS series (4.75V ~ 5.25V) is a subset of the 74ALS specification and presents no compatibility issues in standard 5V logic applications.

Frequently Asked Questions (FAQ)

Q: Can the SN74LS33D and SN74LS33DR be used interchangeably with the SN74ALS33AD?

A: Yes. Both parts implement identical logic functions (4-channel, 2-input NOR gate with open collector output), maintain the same pin configuration in the 14-SOIC package, and meet all specified electrical parameters including input logic levels, output current capability, and operating temperature range.

Q: What is the difference between SN74LS33D and SN74LS33DR?

A: The primary difference is packaging format. SN74LS33D is supplied in bulk packaging, while SN74LS33DR is supplied in tape and reel format. Both parts are electrically identical. Tape and reel packaging is optimized for automated pick-and-place assembly, while bulk packaging is suitable for manual assembly or lower-volume applications.

Q: Why does the SN74LS33 have a narrower supply voltage range than the SN74ALS33AD?

A: The 74LS series specifies 4.75V ~ 5.25V, while the 74ALS series specifies 4.5V ~ 5.5V. The 74LS range is a subset of the 74ALS range. In standard 5V logic applications where supply voltage is regulated to 5V ±5%, both parts operate identically. The narrower specification reflects the tighter tolerance capability of the 74LS process technology.

Q: Are there any compliance or certification differences between the substitute parts?

A: SN74LS33DR includes ROHS3 compliance and REACH unaffected status, matching the original SN74ALS33AD. SN74LS33D compliance information is not provided in the available data. If regulatory compliance is a design requirement, SN74LS33DR is the recommended selection.

Q: What is the propagation delay difference between the main part and substitutes?

A: The SN74ALS33AD specifies 33ns maximum propagation delay at 5V with 50pF load. Both SN74LS33D and SN74LS33DR specify 32ns maximum propagation delay at 5V with 45pF load. The substitutes demonstrate equivalent or superior timing performance.

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