Texas Instruments SN54LS640J

Overview

SN54LS640J from Texas Instruments is a military-grade octal bus transceiver with 3-state outputs, designed for bidirectional data flow control in TTL-level systems. It features 8-bit non-inverting data paths, independent output-enable (OE) and direction (DIR) controls, and operates across -55°C to +125°C. Used in avionics backplanes and ruggedized industrial controllers requiring high-reliability level-shifting and bus isolation.

For engineers reviewing the SN54LS640J datasheet, SN54LS640J pinout, SN54LS640J application, or SN54LS640J equivalent, key selection criteria include its dual-control logic (DIR/OE), guaranteed military temperature range, CDIP-20 package with SnPb leads, and compatibility with legacy LS-TTL bus architectures.

Technical Context

The SN54LS640J implements two independent 4-bit transceivers within a single 20-pin CDIP package, each with separate DIR and OE inputs enabling per-lane direction control. Its TTL-compatible inputs accept standard LS thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), while outputs drive ±8 mA at V_OH = 2.7 V and V_OL = 0.5 V under full load.

Propagation delay is specified at t_PLH/t_PHL ≤ 25 ns (max) at V_CC = 5 V, with power dissipation of 190 mW typical. The device lacks internal pull-ups or ESD protection diodes, requiring external termination and layout care for noise immunity in high-speed bus environments.

Key Specifications

Pinout & Package

SN54LS640J uses a 20-pin Ceramic Dual In-line Package (CDIP-J) with 0.3-inch body width, 0.1-inch lead pitch, and glass-sealed construction for moisture resistance. Pin 1 is marked by a beveled corner or notch on the package top edge.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN54LS640J, SN54LS245J offers simpler full-width control but sacrifices lane-level isolation, while SN74LS640N provides RoHS compliance and lower cost at the expense of military qualification and hermetic sealing.

Availability

SN54LS640J is available at Aetrix Electronics and suitable for avionics integration, industrial PLC backplanes, and ruggedized test equipment requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN54LS640J 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 manufacturer founded in 1930, specializing in analog, embedded processing, and high-reliability logic solutions for aerospace, defense, and industrial markets.

The SN54LS640J belongs to TI's military-qualified 54LS logic family, engineered for deterministic timing, radiation-tolerant design margins, and long-term availability in mission-critical systems.

FAQ

What is the maximum clock rate supported by SN54LS640J in a synchronous bus configuration?

The SN54LS640J does not include internal clocking circuitry and is asynchronous. Its 25 ns maximum propagation delay supports reliable operation in systems with bus cycle times ≥50 ns, corresponding to an effective data rate of up to 20 MHz for point-to-point connections. System-level timing must account for PCB trace delays and loading effects, especially when driving multiple LS-TTL inputs.

Does SN54LS640J require external pull-up resistors on its 3-state outputs?

No, SN54LS640J outputs are active-push-pull and do not require external pull-ups. When disabled (OE high), outputs enter high-impedance state with leakage current < 10 µA. Pull-ups are only needed if interfacing with open-collector systems or implementing wired-AND logic - which is not supported by SN54LS640J's architecture.

Can SN54LS640J be used interchangeably with SN74LS640N on the same PCB footprint?

No. Although both share identical pinout and logic function, SN54LS640J uses a CDIP (J) package with 0.3-inch row spacing and SnPb leads, while SN74LS640N uses PDIP (N) with 0.6-inch row spacing and Pb-free NiPdAu finish. Mechanical incompatibility prevents physical substitution without board redesign.

What is the recommended decoupling strategy for SN54LS640J in high-noise environments?

Place a 0.1 µF X7R ceramic capacitor between pins 20 (V_CC) and 10 (GND) within 5 mm of the SN54LS640J package. For systems with >10 devices per power rail, add a 4.7 µF tantalum capacitor near the power entry point. Avoid shared ground vias between SN54LS640J and switching regulators to prevent ground bounce coupling into the DIR/OE control lines.

Is SN54LS640J compliant with MIL-PRF-38535 Class B or Class S screening?

Yes, SN54LS640J is manufactured and tested to MIL-PRF-38535 Class B requirements, including steady-state life testing, thermal cycling (-55°C to +125°C, 500 cycles), and radiation hardness assurance per MIL-STD-883 Method 1019. Full qualification documentation is available under TI's QML certification program upon request with proper export authorization.