Texas Instruments SN54LS173AJ

Overview

SN54LS173AJ from Texas Instruments is a military-grade 4-bit D-type register with 3-state outputs, designed for bus-organized systems requiring high noise immunity and direct TTL bus interfacing. It features gated data-enable (G1/G2), independent clock control, asynchronous clear (CLR), and dual output-control inputs (M/N) enabling precise bus arbitration. Operates across –55°C to 125°C with 50 MHz max clock frequency and 18 ns typical propagation delay.

For engineers reviewing the SN54LS173AJ datasheet, SN54LS173AJ pinout, SN54LS173AJ application, or SN54LS173AJ equivalent, key selection criteria include its military temperature rating, 3-state output disable timing asymmetry (faster disable than enable), TTL-compatible input thresholds, low 19 mA max supply current, and CDIP (J) package suitability for ruggedized embedded control and avionics data paths.

Technical Context

The SN54LS173AJ implements four independent edge-triggered D flip-flops with fully decoded 3-state output control logic. Its dual output-enable inputs (M/N) operate in active-low AND logic: both must be low for normal Q-output drive; either high forces high-impedance state-decoupled from clock activity. Data loading is synchronous on positive CLK edge only when G1 and G2 are both low.

Asynchronous CLR resets all four flip-flop outputs to low regardless of clock or enable states. Input thresholds meet LS-TTL specifications (VIL = 0.7 V, VIH = 2.0 V), and output drive capability supports up to 49 parallel outputs on a shared bus driving one normalized 54/74LS load-enabling dense bus buffer implementations without external pull-ups or interface logic.

Key Specifications

Pinout & Package

SN54LS173AJ is supplied in a 16-pin Ceramic Dual In-line Package (CDIP, J package), hermetically sealed for high-reliability operation in harsh environments. Pin layout matches industry-standard 16-pin DIP footprint with 0.3-inch body width and 0.1-inch lead pitch.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 4-bit D-type register with 3-state output applications.

Compared with SN54LS173AJ, SNJ54LS173AJ offers identical functionality with enhanced screening for mission-critical space use, while SN54173J trades speed and efficiency for broader legacy compatibility-making SN54LS173AJ the optimal balance of performance, ruggedness, and supply assurance for new military designs.

Availability

SN54LS173AJ is available at Aetrix Electronics and suitable for avionics data buffering, secure communication controllers, ruggedized industrial PLC I/O modules, and test equipment digital pattern generation requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN54LS173AJ 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 specializing in analog, embedded processing, and high-reliability logic solutions for aerospace, defense, and industrial markets.

The SN54LS173AJ belongs to TI's military 54LS logic family, engineered for deterministic timing, noise-immune bus interfacing, and operation in extreme environmental conditions-targeting applications where failure is not an option.

FAQ

What is the maximum clock frequency supported by the SN54LS173AJ?

The SN54LS173AJ supports a maximum clock frequency of 50 MHz under recommended operating conditions (VCC = 4.5 V to 5.5 V, TA = –55°C to 125°C). This value is validated per the SDLS067A datasheet switching characteristics table for SN54LS173A devices at VCC = 5 V and TA = 25°C, with derating applied for full temperature range operation. The 50 MHz rating enables use in high-speed digital control and instrumentation applications where precise 4-bit latching is required.

Does the SN54LS173AJ have true 3-state outputs, and how are they controlled?

Yes, the SN54LS173AJ features true 3-state (high-impedance) outputs controlled independently of the clock by two active-low inputs: M (pin 1) and N (pin 2). Both M and N must be low to enable normal Q-output drive (high or low logic levels); asserting either M or N high places all four outputs (1Q–4Q) into high-impedance state. This architecture allows deterministic bus release without waiting for clock edges-critical for avoiding bus contention in multi-master systems.

What is the purpose of the G1 and G2 inputs on the SN54LS173AJ?

The G1 (pin 16) and G2 (pin 15) inputs on the SN54LS173AJ are gated data-enable controls. Both must be held low to permit loading of data from the D inputs (1D–4D) into their respective flip-flops on the next positive clock edge. This dual-gate structure prevents accidental data capture during bus transitions or noise spikes-ensuring that only intentional, coincident enable signals trigger register updates, enhancing system robustness in electrically noisy military environments.

How does the asynchronous CLR function behave relative to clock and enable signals in the SN54LS173AJ?

The asynchronous CLR input (pin 10) on the SN54LS173AJ forces all four Q outputs (1Q–4Q) low immediately upon assertion of a high logic level-regardless of the states of CLK, G1, G2, M, or N. This override behavior is critical for fail-safe initialization, emergency shutdown, or cryptographic zeroization, as it bypasses all synchronous controls and provides sub-30 ns reset response confirmed in the datasheet's timing requirements table.

Is the SN54LS173AJ compatible with standard 5 V TTL logic families?

Yes, the SN54LS173AJ is fully compatible with standard 5 V TTL logic families including 54/74, 54LS/74LS, and 54S/74S. Its input voltage thresholds (VIL = 0.7 V max, VIH = 2.0 V min) and output drive capabilities (IOL = 12 mA, IOH = –1 mA) meet LS-TTL specifications. It can directly interface with and drive up to 49 other SN54LS173AJ outputs on a shared bus while maintaining valid logic levels-eliminating need for external buffers or pull-up resistors.