Texas Instruments SN74AS157NSR

Overview

SN74AS157NSR from Texas Instruments is a quad 2-line-to-1-line data selector/multiplexer with true-output logic, buffered inputs/outputs, and TTL-compatible operation. It selects one of two 4-bit data sources (A or B) under control of the A/B select line and strobes output via G, delivering full-word routing for digital bus management in industrial control and instrumentation systems.

For engineers reviewing the SN74AS157NSR datasheet, SN74AS157NSR pinout, SN74AS157NSR application, or SN74AS157NSR equivalent, key selection criteria include propagation delay (1–6 ns), output drive strength (20 mA sink), operating temperature range (0°C to 70°C), SOP-16 package compatibility, and direct functional equivalence to SN74ALS157A with enhanced speed.

Technical Context

This device implements four independent 2:1 multiplexers in a single IC, each with dedicated A/B data inputs, common strobe (G), and true-output Y. Logic operation follows positive-logic TTL thresholds: VIH = 2 V min, VIL = 0.8 V max, ensuring robust noise immunity in mixed-signal environments.

All outputs are totem-pole (non-open-collector), fully buffered, and capable of driving standard TTL loads. The A/B select line determines source routing across all four channels simultaneously, while G enables/disables all outputs-supporting synchronized data gating in synchronous digital systems.

Key Specifications

Pinout & Package

SOP-16 (NS) package: 16-pin small-outline plastic, 1.27 mm pitch, 10.0 mm × 4.4 mm body, 2.00 mm max height, RoHS-compliant NiPdAu lead finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ALS157ANSR and SN74LS157N, SN74AS157NSR delivers 3× faster propagation, 2.5× higher sink current, and SOP-16 packaging optimized for automated assembly - making it the preferred choice for new designs requiring timing-critical bus management.

Availability

SN74AS157NSR is available at Aetrix Electronics and suitable for industrial control systems, automated test equipment, legacy bus interface modules, and embedded instrumentation requiring stable component supply across extended production lifecycles.

Supply support for SN74AS157NSR 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.

SN74AS157NSR belongs to TI's Advanced Schottky TTL logic family, engineered for high-speed digital systems where propagation delay, noise immunity, and TTL interoperability are critical design requirements.

FAQ

What is the maximum clock frequency supported by SN74AS157NSR in a data selection application?

The SN74AS157NSR does not operate on a clock signal-it is asynchronous. Its usable data rate depends on propagation delay and system setup/hold timing. With worst-case tPHL/tPLH of 6 ns and 11 ns respectively, SN74AS157NSR supports reliable 4-bit word selection in systems with ≥15 ns minimum cycle time, corresponding to effective throughput up to ~65 MHz in pipelined configurations. Always verify timing margins using actual board trace lengths and load capacitance.

Does SN74AS157NSR support 3.3-V logic interfaces?

No, SN74AS157NSR is strictly a 5-V TTL device. Its input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) and output voltage levels (VOH ≈ VCC − 2 V, VOL ≤ 0.5 V) are specified only for VCC = 4.5–5.5 V operation. Direct connection to 3.3-V CMOS or LVTTL systems risks undriven inputs or excessive current injection; level-shifting circuitry is required for interoperability.

Can SN74AS157NSR replace SN74AS157N in an existing PDIP-based design?

Yes, SN74AS157NSR is functionally identical to SN74AS157N but in SOP-16 instead of PDIP-16. Pin assignments match exactly per TI's standardized 16-pin logic layout (pin 1 = 1A, pin 16 = VCC, etc.). However, the package change requires PCB redesign: SN74AS157NSR uses 1.27 mm pitch gull-wing leads versus 2.54 mm through-hole spacing, necessitating new footprint, stencil, and reflow profile.

What is the purpose of the NC pins on SN74AS157NSR?

SN74AS157NSR has no NC (No Connect) pins. All 16 pins are electrically assigned: pins 1–7, 9–15 carry signals (data, select, strobe, outputs), pin 8 is GND, and pin 16 is VCC. This differs from some ceramic or military variants (e.g., FK package) which include NC pins; the SOP-16 NS package utilizes every pin for defined I/O or power functions.

How does the strobe (G) input affect output behavior in SN74AS157NSR?

In SN74AS157NSR, the G input is an active-low enable: when G = LOW, outputs 1Y–4Y reflect the selected A/B data; when G = HIGH, all outputs are forced LOW regardless of A/B or data states. This differs from enable-active-HIGH multiplexers and provides fail-safe default-low behavior during reset or fault conditions - critical for preventing spurious bus contention in safety-rated systems.