Texas Instruments SN74ALS641ANSR

Overview

SN74ALS641ANSR from Texas Instruments is an octal bidirectional bus transceiver with true logic, designed for asynchronous two-way data communication between A and B buses in industrial and legacy computing systems. It features direction-control (DIR) and output-enable (OE) inputs, 20-pin SOP (NS) package, 0°C to 70°C operating range, and supports 48 mA low-level output current in the -1 variant (this part is non–-1; IOL = 24 mA).

For engineers reviewing the SN74ALS641ANSR datasheet, SN74ALS641ANSR pinout, SN74ALS641ANSR application, or SN74ALS641ANSR equivalent, key selection criteria include bidirectional bus isolation timing (tPLH/tPHL ≤ 25 ns), 5 V TTL-compatible logic levels, 20-pin SOP thermal and layout compatibility, and ALS family power-performance tradeoffs versus AS/LS variants.

Technical Context

The SN74ALS641ANSR implements a dual-rail 8-bit transceiver architecture with independent DIR and OE control, enabling selective A→B or B→A data flow without bus contention. Its three-state outputs provide high-impedance isolation when OE is high, and its ALS logic family delivers lower power than AS while maintaining higher speed than standard LS.

It operates strictly at 5 V (4.5–5.5 V), uses TTL input thresholds (VIH = 2 V, VIL = 0.8 V), and exhibits asymmetric propagation delays: tPHL (3–18 ns) is faster than tPLH (5–25 ns) due to internal bipolar transistor biasing. Output drive strength is rated at 24 mA sink per pin under recommended conditions.

Key Specifications

Pinout & Package

SOP (NS) 20-pin surface-mount package, 0.300-inch body width, 1.27 mm pitch, 2.65 mm max height, RoHS-compliant NIPDAU finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ALS641AN, SN74ALS641ANSR offers identical functionality in a space-saving SOP package ideal for production PCBs; compared with SN74AS641NSR, it trades speed for lower power and better noise immunity in electrically noisy industrial environments.

Availability

SN74ALS641ANSR is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy computer upgrades, test equipment signal routing, and programmable logic interconnects requiring stable component supply across long-lifecycle programs.

Supply support for SN74ALS641ANSR 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 solutions for industrial, automotive, and communications markets.

The SN74ALS641ANSR belongs to TI's legacy 74ALS logic family, engineered for reliable 5 V TTL bus interfacing in cost-sensitive, thermally constrained industrial control and retro-computing applications.

FAQ

What is the maximum clock/data rate supported by SN74ALS641ANSR?

The SN74ALS641ANSR does not operate on a clock; it is an asynchronous transceiver. Its usable data rate depends on propagation delay and system timing margins. With tPHL ≤ 18 ns and tPLH ≤ 25 ns (CL = 50 pF), it supports bus cycle times down to ~50 ns - suitable for 20 MHz burst-mode operation in well-designed 5 V TTL systems. Always validate timing with actual load and trace capacitance.

Is SN74ALS641ANSR pin-compatible with SN74ALS642ANSR?

No, SN74ALS641ANSR is not pin-compatible with SN74ALS642ANSR. While both are 20-pin SOP transceivers, SN74ALS642A implements inverting logic (A→B data is inverted), altering functional behavior. Pin assignments match, but logic function differs - direct substitution will cause data corruption unless system firmware compensates for inversion.

Does SN74ALS641ANSR support 3.3 V logic levels?

No, SN74ALS641ANSR is a 5 V-only device. Its absolute maximum VCC is 7 V, and recommended operating range is 4.5–5.5 V. Input thresholds (VIH = 2 V, VIL = 0.8 V) are TTL-defined; 3.3 V logic may not reliably meet VIH, and VCC < 4.5 V risks incorrect output states. Use level translators like SN74LVC4245 for 3.3 V ↔ 5 V interfacing.

What is the thermal resistance (θJA) of the SN74ALS641ANSR SOP package?

Texas Instruments does not publish θJA for SN74ALS641ANSR in the SDAS300 datasheet. As a legacy ALS device in SOP-20 (NS), typical θJA is ~120°C/W with standard JEDEC 2-layer board layout. For thermal design, assume worst-case ICC = 47 mA at 5.5 V → ~260 mW dissipation; keep ambient < 60°C and ensure adequate copper area under the package for reliability.

Can SN74ALS641ANSR replace SN74LS641 in an existing design?

Yes, SN74ALS641ANSR can directly replace SN74LS641 in most cases: same pinout, true logic, and TTL-compatible thresholds. Key improvements include faster speed (LS tPLH ≈ 35 ns vs ALS 25 ns) and lower power (ALS ICC ~35 mA vs LS ~60 mA at 5 V). Confirm that the -1 suffix isn't required - SN74ALS641ANSR has 24 mA IOL, matching standard LS, not the enhanced 48 mA of ALS641A-1.