DM74LS191N Equivalent & Substitute Parts

Part Overview

The DM74LS191N is a 4-bit binary counter IC manufactured by onsemi, housed in a 16-DIP package. This component functions as a synchronous counter with up/down capability, operating at a maximum count rate of 20 MHz. The part is classified as obsolete, making identification of suitable alternatives essential for ongoing production and maintenance applications. Substitute parts must maintain functional equivalence in counter operation, package compatibility, and electrical specifications to ensure direct replacement capability.

Key Parameters

Parameter	Value
Logic Type	Binary Counter
Number of Bits per Element	4
Direction	Up, Down
Timing	Synchronous
Trigger Type	Positive Edge
Count Rate	20 MHz
Voltage - Supply	4.75 V ~ 5.25 V
Operating Temperature	0°C ~ 70°C
Package / Case	16-DIP (0.300", 7.62mm)
Mounting Type	Through Hole

Substitute Part Grouping Explanation

Substitution eligibility for the DM74LS191N is determined by the following critical parameters:

Primary Substitution Criteria:

Logic Type: Binary Counter
Number of Bits per Element: 4 bits
Direction: Up/Down capability
Timing: Synchronous operation
Trigger Type: Positive Edge
Package / Case: 16-DIP (0.300", 7.62mm)
Mounting Type: Through Hole
Voltage - Supply: 4.75 V ~ 5.25 V compatibility
Operating Temperature: 0°C ~ 70°C range

The SN74LS191N (Texas Instruments) qualifies as a direct equivalent, meeting all functional and physical parameters. The SN74LS194AN, while sharing the same package and voltage specifications, functions as a bidirectional shift register rather than a binary counter, making it unsuitable for direct substitution in applications requiring counter functionality.

Parameter Comparison

Parameter	DM74LS191N (onsemi)	SN74LS191N (Texas Instruments)	SN74LS194AN (Texas Instruments)
Logic Type	Binary Counter	Binary Counter	Register, Bidirectional
Number of Bits per Element	4	4	4
Direction	Up, Down	Up, Down	N/A
Timing	Synchronous	Synchronous	N/A
Trigger Type	Positive Edge	Positive Edge	N/A
Count Rate / Speed	20 MHz	25 MHz	N/A
Voltage - Supply	4.75 V ~ 5.25 V	4.75 V ~ 5.25 V	4.75 V ~ 5.25 V
Operating Temperature	0°C ~ 70°C	0°C ~ 70°C	0°C ~ 70°C
Package / Case	16-DIP (0.300", 7.62mm)	16-DIP (0.300", 7.62mm)	16-DIP (0.300", 7.62mm)
Mounting Type	Through Hole	Through Hole	Through Hole
Product Status	Obsolete	Active	Active
RoHS Status	RoHS non-compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

SN74LS191N (Texas Instruments) is the appropriate substitute for the obsolete DM74LS191N. Both parts are 4-bit binary counters with identical functional specifications, package geometry, and electrical operating ranges. The SN74LS191N offers the additional advantage of active product status and ROHS3 compliance, ensuring long-term availability and regulatory alignment. The count rate specification of 25 MHz for the SN74LS191N exceeds the 20 MHz requirement of the original part, providing performance margin.

SN74LS194AN is not suitable as a substitute. Although it shares the same 16-DIP package and voltage specifications, it is a bidirectional shift register, not a binary counter. Functional incompatibility makes this part unsuitable for applications requiring counter operation.

Frequently Asked Questions (FAQ)

Q: Can the SN74LS191N directly replace the DM74LS191N without circuit modifications?

A: Yes. The SN74LS191N is functionally and physically equivalent. Both parts are 4-bit synchronous binary counters with up/down capability, identical pin configurations in 16-DIP packages, and matching voltage supply and temperature specifications.

Q: What is the difference between the DM74LS191N and SN74LS194AN?

A: The DM74LS191N is a binary counter; the SN74LS194AN is a bidirectional shift register. These are distinct logic functions with different operational characteristics and pin assignments. The SN74LS194AN cannot perform counter functions and is not interchangeable.

Q: Does the higher count rate of the SN74LS191N (25 MHz vs. 20 MHz) affect compatibility?

A: No. The SN74LS191N's higher count rate specification is a performance advantage. It meets or exceeds all timing requirements of the original DM74LS191N and is fully compatible in applications designed for the 20 MHz specification.

Q: Are there RoHS compliance considerations for substitution?

A: The DM74LS191N is RoHS non-compliant, while the SN74LS191N is ROHS3 compliant. For applications subject to RoHS regulations, the SN74LS191N provides regulatory compliance. For legacy systems without RoHS requirements, both parts are electrically equivalent.

Q: Is the 16-DIP package pinout identical between substitute parts?

A: The SN74LS191N maintains identical pinout to the DM74LS191N as both are 74LS191 series parts. The SN74LS194AN, while also in a 16-DIP package, has a different pinout due to its different logic function and is not pin-compatible.

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