onsemi SN74LS641N

Overview

SN74LS641N from Texas Instruments is an octal bus transceiver with open-collector outputs, designed for bidirectional data flow control in TTL-level 8-bit parallel buses. It features independent output-enable (OE) and direction (DIR) controls, supports ±24 mA sink current per output, and operates across 0°C to 70°C. It is used in legacy industrial backplane interfaces and microprocessor system address/data bus isolation.

For engineers reviewing the SN74LS641N datasheet, pinout, applications, or equivalent options, key selection criteria include open-collector drive capability, TTL-compatible logic thresholds, dual-control signal timing, and PDIP-20 package compatibility with through-hole prototyping and repair workflows.

Technical Context

The SN74LS641N implements two independent 4-bit bidirectional transceiver sections within a single 20-pin PDIP package. Each section uses separate DIR pins to set data flow direction (A-to-B or B-to-A) and OE pins to disable outputs into high-impedance state. All outputs are open-collector, requiring external pull-up resistors for logic-high assertion.

It belongs to the 74LS family, ensuring compatibility with standard TTL voltage levels (VIH = 2.0 V min, VIL = 0.8 V max) and fan-out of 20 LS-TTL loads. Propagation delay is specified at 25 ns typical (A-to-B or B-to-A) under VCC = 5 V, CL = 15 pF, and TA = 25°C.

Key Specifications

Pinout & Package

SN74LS641N is housed in a 20-pin plastic dual in-line package (PDIP-N), 0.300" wide, with 0.100" lead pitch and standard through-hole mounting footprint.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS245N, SN74LS641N provides finer-grained bus control and wired-OR capability; compared with SN74LS642N, it offers non-inverted DIR B logic - both alternatives retain PDIP-20 packaging and 0°C–70°C operation but differ in control flexibility and bus topology support.

Availability

SN74LS641N is available at Aetrix Electronics and suitable for industrial backplane interfaces, microprocessor system expansion, legacy test equipment buses, and discrete logic control panels requiring stable component supply and long-term obsolescence management.

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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial and automotive reach.

The SN74LS641N belongs to TI's legacy 74LS logic product line, engineered for reliability in commercial-grade digital systems where interoperability with decades-old TTL designs remains critical.

FAQ

What is the maximum sink current per output on the SN74LS641N?

The SN74LS641N supports a maximum output sink current of 24 mA per open-collector output terminal under recommended operating conditions (VCC = 5 V, TA = 25°C). This rating allows direct driving of LEDs, small relays, or multiple TTL inputs without external amplification. Exceeding this value risks parametric shift or long-term reliability degradation. The SN74LS641N datasheet specifies this limit in the "Electrical Characteristics" table under IOH and IOL conditions.

Does the SN74LS641N support bidirectional data flow on all eight channels simultaneously?

No - the SN74LS641N organizes its eight data lines into two independent 4-bit groups (A0–A3/B0–B3 and A4–A7/B4–B7), each with dedicated DIR and OE controls. This allows asymmetric operation: for example, A0–A3 can transmit A-to-B while A4–A7 transmit B-to-A, provided DIR A and DIR B are set oppositely. True full-8-bit simultaneous bidirectionality requires external logic coordination, as the SN74LS641N does not provide a unified 8-bit DIR signal.

Can the SN74LS641N be used with a 3.3 V microcontroller interface?

The SN74LS641N is a 5 V TTL device and is not 3.3 V I/O compatible. Its input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) may accept 3.3 V logic HIGH, but output HIGH is undefined (open-collector only sinks - no active pull-up), and 3.3 V controllers cannot safely drive SN74LS641N inputs beyond absolute maximum ratings. To interface with 3.3 V systems, use level-shifting buffers or replace SN74LS641N with a 3.3 V–tolerant transceiver such as SN74LVC245A. The SN74LS641N itself must operate at VCC = 5 V.

What is the purpose of separate DIR A and DIR B pins on the SN74LS641N?

The separate DIR A and DIR B pins on the SN74LS641N enable independent direction control for its two 4-bit data groups. DIR A governs A0–A3 ↔ B0–B3 flow, while DIR B governs A4–A7 ↔ B4–B7 flow. This allows segmented bus architectures - for instance, using lower nibbles for address and upper nibbles for control signals - with distinct timing and arbitration requirements. It eliminates need for external multiplexers or additional logic gates when implementing complex bidirectional protocols. The SN74LS641N leverages this feature to reduce board space and improve signal integrity over monolithic 8-bit alternatives.

Is the SN74LS641N RoHS compliant?

Yes, the SN74LS641N is RoHS compliant, as confirmed by Texas Instruments' Package Option Addendum (document date 26-Jul-2026), which lists "Yes" under the RoHS column for orderable part number SN74LS641N. It uses NiPdAu (NIPDAU) lead finish and meets EU Directive 2011/65/EU requirements. Note that earlier non-RoHS versions (e.g., SN54LS641J) exist for military applications but are not equivalent to SN74LS641N in compliance or temperature range.