Texas Instruments SN74AS157NS

Overview

SN74AS157NS from Texas Instruments is a quad 2-line-to-1-line data selector/multiplexer with true (non-inverting) output logic, designed for high-speed digital signal routing in TTL-compatible systems. It features buffered inputs/outputs, a common strobe (G) enable, and operates across 0°C to 70°C at 4.5–5.5 V supply. It selects one of two 4-bit data sources (A or B) and routes the selected word to four independent outputs (1Y–4Y), supporting real-time bus arbitration in legacy computing and industrial control interfaces.

For engineers reviewing the SN74AS157NS datasheet, SN74AS157NS pinout, SN74AS157NS application, or SN74AS157NS equivalent, this page delivers verified electrical specs, package mapping, functional behavior per input state, timing performance under load, and validated drop-in alternatives - all specific to the NS (16-pin plastic DIP) variant.

Technical Context

The SN74AS157NS implements four independent 2:1 multiplexers sharing a single A/B select line and global strobe (G) enable. Its AS (Advanced Schottky) logic family delivers sub-6 ns propagation delay (tPHL/tPLH) from data inputs (A/B) to outputs (Y) under 50 pF load, with guaranteed 1 ns minimum pulse width tolerance. All outputs are totem-pole (not open-collector), providing symmetrical drive capability: ±2 mA high-level and 20 mA low-level output current.

It uses standard positive-logic control: G = L enables output, G = H forces all Y outputs low; A/B = L selects source A, A/B = H selects source B. Input thresholds meet TTL-compatible VIH ≥ 2.0 V and VIL ≤ 0.8 V, ensuring interoperability with 74LS, 74ALS, and earlier 74xx families without level-shifting.

Key Specifications

Pinout & Package

SN74AS157NS is supplied in a 16-pin plastic dual in-line package (PDIP), designated "NS" by Texas Instruments. The package has 300-mil body width, 0.3-inch row spacing, and standard through-hole lead form for wave or hand soldering.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quad 2:1 multiplexer applications.

Compared with SN74AS157NS, SN74ALS157N trades 3× longer propagation delay for ~60% lower quiescent current, while SN74F157N offers intermediate speed and drive strength at lower unit cost - all three share identical 16-pin DIP footprint and functional truth table.

Availability

SN74AS157NS is available at Aetrix Electronics and suitable for computer bus arbitration, industrial PLC I/O multiplexing, digital test equipment channel switching, and legacy instrumentation data path control requiring stable component supply and long-term obsolescence management.

Supply support for SN74AS157NS 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 innovator founded in 1930, delivering analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74AS157NS belongs to TI's legacy 74AS logic family, engineered for high-speed, low-power TTL-compatible digital interfacing in systems where timing predictability and robust drive capability are critical.

FAQ

What is the maximum operating frequency supported by the SN74AS157NS?

The SN74AS157NS does not specify a maximum clock frequency directly, but its worst-case propagation delay (tPHL/tPLH) is 10.5 ns (G → Y) and 6 ns (A/B → Y). Assuming setup/hold times are met, it reliably supports data toggling up to approximately 100 MHz in well-terminated, low-capacitance environments - confirmed by measured switching characteristics at CL = 50 pF and RL = 500 Ω.

Does the SN74AS157NS support 3.3 V operation?

No, the SN74AS157NS is specified only for 4.5 V to 5.5 V supply operation. Its input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and output voltage levels (VOH ≥ VCC − 2 V, VOL ≤ 0.5 V) are designed for 5 V TTL compatibility. Operating at 3.3 V violates recommended conditions and risks incorrect logic interpretation or excessive ICC.

Is the SN74AS157NS pin-compatible with the SN74LS157?

Yes - the SN74AS157NS uses the same 16-pin DIP (NS) package and identical pinout as SN74LS157N, SN74ALS157N, and SN74F157N. All share identical signal assignments (1A–4B, 1Y–4Y, G, A/B, VCC, GND), enabling direct replacement in existing layouts where speed and drive improvements are acceptable.

What is the purpose of the G (strobe) pin on the SN74AS157NS?

The G pin is an active-low enable input: when G = LOW, the selected data (A or B, per A/B pin state) appears at outputs 1Y–4Y; when G = HIGH, all outputs are forced LOW regardless of A/B or data inputs. This provides synchronous output gating - essential for bus isolation, time-division multiplexing, and hazard-free state transitions in synchronous digital systems.

Can the SN74AS157NS drive LEDs directly?

Yes - with IOL = 20 mA per output, the SN74AS157NS can directly sink current for standard 5 mm LEDs (typically 10–20 mA) when configured with appropriate series resistors. For example, at VCC = 5 V and VOL = 0.5 V, a 220 Ω resistor yields ~20 mA drive. Avoid connecting LEDs anode-to-VCC without current limiting, as output high-drive (IOH = −2 mA) is insufficient for sourcing.