74AC191SC Binary Counter IC Equivalent & Substitute Parts

Part Overview

The 74AC191SC is a 4-bit binary counter IC manufactured by onsemi, designed for synchronous up/down counting applications with a maximum count rate of 133 MHz. This component is classified as obsolete, making equivalent and substitute parts necessary for ongoing production and maintenance applications. The 74AC191SC operates across a wide supply voltage range of 2V to 6V and is housed in a 16-SOIC surface mount package, suitable for modern PCB assembly processes.

Substiute Parts

74AC191SC

onsemiIn Stock: 208774AC191SC Datasheet

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SN74HC191D

Texas InstrumentsIn Stock: 1925SN74HC191D Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitution of the 74AC191SC is determined by the following critical parameters that must remain consistent:

• Logic Function: Binary counter with 4-bit capacity, up/down counting capability
• Timing Architecture: Synchronous operation with positive edge triggering
• Electrical Specifications: Supply voltage range 2V to 6V, operating temperature -40°C to 85°C
• Physical Package: 16-SOIC surface mount form factor with identical pin configuration
• Count Rate Performance: Minimum 24 MHz operational capability (substitute may have lower maximum count rate than original)

The SN74HC191D from Texas Instruments meets all substitution criteria. While the 74HC191D exhibits a reduced maximum count rate of 24 MHz compared to the 74AC191SC's 133 MHz, it maintains functional equivalence for standard counting applications within this performance envelope. Both parts share identical pin configurations, package geometry, and core counter functionality.

Parameter Comparison

Engineering Selection Recommendations

The SN74HC191D represents the primary substitute for the obsolete 74AC191SC. Selection should be based on the following engineering criteria:

For applications requiring maximum count rate performance above 24 MHz: The 74AC191SC's 133 MHz capability cannot be matched by the SN74HC191D. In such cases, alternative high-speed counter architectures must be evaluated outside the 74HC/74AC series.

For standard counting applications operating below 24 MHz: The SN74HC191D provides full functional compatibility with identical pin configuration and package geometry, enabling direct board-level substitution.

Compliance and availability considerations: The SN74HC191D carries ROHS3 compliance certification and Last Time Buy status, indicating continued manufacturer support through a defined end-of-life window. Both parts maintain REACH Unaffected status and unlimited moisture sensitivity rating, suitable for standard PCB assembly and storage conditions.

Reset functionality: The SN74HC191D includes asynchronous reset capability, providing additional functional flexibility compared to the 74AC191SC specification.

Frequently Asked Questions (FAQ)

Q: Can the SN74HC191D be used as a direct replacement for the 74AC191SC in all applications?

A: Direct substitution is valid for applications where the counter operates below 24 MHz. The SN74HC191D maintains identical pin configuration, package footprint, and core counter functionality. Applications requiring count rates above 24 MHz require alternative component selection.

Q: What is the primary difference between these two parts?

A: The maximum count rate differs significantly. The 74AC191SC operates at 133 MHz, while the SN74HC191D operates at 24 MHz. Both parts share identical 4-bit binary counter architecture, synchronous timing, up/down direction control, and 16-SOIC packaging.

Q: Are there any compliance or regulatory differences between the 74AC191SC and SN74HC191D?

A: Both parts maintain REACH Unaffected status and unlimited moisture sensitivity rating. The SN74HC191D carries ROHS3 compliance certification. Both parts are suitable for standard industrial and commercial applications.

Q: Does the SN74HC191D require different PCB layout or assembly procedures?

A: No. The SN74HC191D uses identical 16-SOIC surface mount packaging with the same pin configuration and physical dimensions as the 74AC191SC. Existing PCB layouts and assembly processes require no modification.

Q: What is the significance of the "Last Time Buy" status for the SN74HC191D?

A: Last Time Buy status indicates that Texas Instruments has defined an end-of-life window for this component. Customers requiring long-term supply should plan accordingly and consider inventory requirements before the discontinuation date.

Q: Can the asynchronous reset function of the SN74HC191D be ignored if not required by the application?

A: Yes. The asynchronous reset input can remain unconnected or tied to the inactive state if the application does not require this functionality. The core counter operation remains identical to the 74AC191SC.