Texas Instruments SN74LS641N

Overview

SN74LS641N from Texas Instruments is an octal bus transceiver with open-collector outputs, designed for bidirectional data flow control in TTL-level parallel bus systems. It features 8-bit non-inverting data paths, active-low output-enable (OE̅) control, and operates across 0°C to 70°C. Used in legacy industrial backplanes and microprocessor address/data bus isolation.

For engineers reviewing the SN74LS641N datasheet, SN74LS641N pinout, SN74LS641N application, or SN74LS641N equivalent, this page delivers verified electrical specs, package dimensions, functional role in bus arbitration, and validated drop-in alternatives for legacy system maintenance and redesign.

Technical Context

The SN74LS641N implements dual 4-bit bidirectional bus transceivers in a single 20-pin PDIP package. Each half supports independent direction control via separate OE̅ inputs and shares common A- and B-side I/O terminals.

Its open-collector outputs enable wired-AND logic, bus contention avoidance, and level translation when pulled up to external V_CC. Input thresholds match standard LS-TTL (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), ensuring compatibility with 74LS family logic.

Key Specifications

Pinout & Package

SN74LS641N uses a 20-pin plastic dual in-line package (PDIP-N) with 0.3-inch body width and 0.1-inch lead pitch. Pin 1 is located at the left end of the top row, identified by a notch or dot marking.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal bus transceiver applications.

Compared with SN74LS641N, SN74LS245N offers stronger drive but lacks native wired-AND capability, while SN74LS642N provides identical physical and electrical behavior except for signal polarity - making it the only true functional substitute for non-inverting open-collector bus coupling.

Availability

SN74LS641N is available at Aetrix Electronics and suitable for legacy industrial control upgrades, microprocessor development systems, and test equipment refurbishment requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74LS641N includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial and automotive portfolio coverage.

The SN74LS641N belongs to TI's legacy 74LS logic family, engineered for reliability and interoperability in commercial-grade digital systems requiring TTL-compatible bus interface solutions.

FAQ

What is the primary function of the SN74LS641N in a digital system?

The SN74LS641N serves as an octal bidirectional bus transceiver with open-collector outputs, enabling controlled data flow between two 8-bit parallel buses. Its dual OE̅ inputs allow independent activation of two 4-bit segments, and its open-collector architecture supports wired-AND bus sharing - critical for contention-free communication in legacy microprocessor and industrial backplane designs. The SN74LS641N is specifically optimized for TTL-level signal integrity and timing compatibility within 74LS-based systems.

Can SN74LS641N replace SN74LS245N in an existing design?

No, SN74LS641N cannot directly replace SN74LS245N without circuit modification. While both are octal transceivers, SN74LS641N has open-collector outputs and dual OE̅ pins, whereas SN74LS245N uses tri-state outputs and a single DIR pin for direction control. Substituting them would require removing external pull-up resistors (if present for SN74LS245N) and revising enable logic - and would eliminate wired-AND capability. The SN74LS641N is not a pin-compatible or functional drop-in for SN74LS245N.

What is the maximum sink current per output on SN74LS641N?

The SN74LS641N guarantees a minimum output sink current (I_OL) of 24 mA per pin at V_CC = 5 V and T_A = 25°C, with typical values reaching 30 mA. This rating allows the SN74LS641N to drive up to 20 standard LS-TTL inputs or terminate long parallel bus traces with appropriate pull-up resistors. Exceeding 24 mA continuously may cause output voltage degradation or thermal stress, so load calculations must remain within this spec for reliable SN74LS641N operation.

Does SN74LS641N support 3.3 V logic levels?

No, SN74LS641N is strictly a 5 V TTL device and does not support 3.3 V logic levels. Its input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) and output voltages (V_OL ≤ 0.5 V, V_OH undefined - open-collector) assume a 5 V pull-up. Driving SN74LS641N inputs from 3.3 V CMOS sources risks marginal high-level recognition, and connecting its outputs to 3.3 V–tolerant inputs requires careful pull-up selection to avoid exceeding absolute maximum ratings. For mixed-voltage systems, level translators or 3.3 V–compatible transceivers (e.g., SN74LVC245A) should be used instead of SN74LS641N.

Is there a surface-mount version of SN74LS641N available?

Yes, SN74LS641NSR is the SOP-20 (small-outline package) surface-mount variant of SN74LS641N, with identical logic function, timing, and electrical specifications. It uses a 20-pin NS package (JEDEC MS-012), is RoHS-compliant, and has a moisture sensitivity level (MSL) rating of Level-1 at 260°C peak reflow. SN74LS641NSR shares the same part marking "74LS641" and operates across 0°C to +70°C - making it a direct drop-in replacement for board space-constrained or automated assembly applications requiring SN74LS641N functionality.