Texas Instruments SN74173N

Overview

SN74173N from Texas Instruments is a 4-bit D-type register with 3-state outputs, designed for bus-oriented TTL systems. It features independent clock and gated data-enable (G1/G2) and output-control (M/N) inputs, supports parallel load and hold modes, and delivers 35 MHz maximum clock frequency with 23 ns typical propagation delay. It operates from 4.75 V to 5.25 V at 0°C to 70°C and drives up to 128 outputs on a shared bus.

For engineers reviewing the SN74173N datasheet, SN74173N pinout, SN74173N application, or SN74173N equivalent, key selection considerations include its 16-pin PDIP (N) package, TTL-compatible 3-state bus interface capability, clear-synchronized synchronous operation, and compatibility with legacy 74-series logic families in industrial control and data acquisition systems.

Technical Context

The SN74173N implements four edge-triggered D-type flip-flops with fully independent clocking and dual-gated data enable (G1, G2), enabling precise control of parallel data loading without affecting internal state retention. Its 3-state output drivers use totem-pole architecture with high-impedance disable controlled separately by M and N inputs - disabling outputs does not interfere with clocked sequential operation.

It adheres to standard TTL voltage thresholds (VIH = 2 V, VIL = 0.8 V), supports 16 mA low-level and –5.2 mA high-level output drive, and meets absolute maximum ratings including –0.5 V to 5.5 V input voltage and 78°C/W thermal impedance in the N package. Timing is characterized for 25 ns minimum clock pulse width and 10 ns data setup/hold times.

Key Specifications

Pinout & Package

SN74173N is supplied in a 16-pin plastic dual in-line package (PDIP-N), with 0.3-inch body width and through-hole mounting. Pin spacing is 0.1 inch, and the package is RoHS-compliant with NiPdAu lead finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74173N, SN74LS173AN offers higher speed and lower power at the cost of stricter input thresholds, while SN74ALS173N further improves noise margin and timing consistency - both retain pin compatibility but differ in drive strength and DC characteristics.

Availability

SN74173N is available at Aetrix Electronics and suitable for industrial PLC I/O expansion, legacy computer bus buffering, and test equipment pattern generation requiring stable component supply across long-lifecycle programs.

Supply support for SN74173N 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 with broad industrial and automotive reach.

The SN74173N belongs to TI's legacy 74-series TTL logic family, engineered specifically for robust, pin-compatible replacement in bus-oriented digital systems requiring synchronous 4-bit storage with 3-state control.

FAQ

What is the maximum clock frequency supported by the SN74173N?

The SN74173N supports a maximum clock frequency of 35 MHz under recommended operating conditions (VCC = 4.75 V to 5.25 V, TA = 0°C to 70°C). This rating is validated with CL = 50 pF and RL = 400 Ω load conditions, and reflects guaranteed timing performance across the commercial temperature range. The SN74173N datasheet specifies 25 MHz minimum clock pulse duration (tw) to ensure reliable edge triggering.

Does the SN74173N support asynchronous reset, and how is it implemented?

Yes, the SN74173N features an asynchronous active-high clear input (pin 10, CLR). When CLR is driven high, all four Q outputs (1Q–4Q) are forced low immediately - independent of clock, G1/G2, or M/N states. This function remains active even when outputs are disabled (M or N high), making it suitable for system-wide initialization. The SN74173N datasheet confirms tPHL (clear-to-output) as 18–27 ns.

How many SN74173N outputs can share a common bus without signal degradation?

Up to 128 SN74173N outputs can be connected to a single common bus while still driving two Series 74 TTL normalized loads. This capability stems from its totem-pole 3-state outputs, which provide strong low-level sinking (16 mA) and sufficient high-level sourcing (–5.2 mA), eliminating need for external pull-ups. Bus contention risk is reduced by design: average output disable time is shorter than enable time.

What are the voltage thresholds for reliable logic-level recognition on the SN74173N inputs?

The SN74173N recognizes VIH ≥ 2.0 V as a valid high-level input and VIL ≤ 0.8 V as a valid low-level input under recommended operating conditions. These thresholds align with standard TTL specifications, ensuring interoperability with 74-series gates, microcontrollers, and FPGAs with TTL-compatible I/O. Input clamp voltage is –1.5 V, supporting transient protection when VI < GND.

Is the SN74173N pin-compatible with other members of the '173 family, such as the SN74LS173A?

Yes, the SN74173N is pin-compatible with SN74LS173AN and SN74ALS173N in the 16-pin PDIP (N) package - all share identical pinout, terminal functions, and physical dimensions. However, electrical differences exist: SN74173N uses standard TTL drive and timing, while LS/ALS variants offer lower power and faster switching. No PCB changes are required for drop-in substitution, but logic threshold and loading behavior must be verified.