Texas Instruments SN74AS157D

Overview

SN74AS157D from Texas Instruments is a quad 2-line-to-1-line data selector/multiplexer IC with true-output logic, designed for high-speed digital signal routing in TTL-compatible systems. It features buffered inputs/outputs, 16-pin SOIC (D) package, 0°C to 70°C operating range, and delivers propagation delays as low as 1 ns (tPHL/tPLH from A/B or G to Y). It is used in address/data bus selection, ALU input multiplexing, and digital test equipment.

For engineers reviewing the SN74AS157D datasheet, SN74AS157D pinout, SN74AS157D application, or SN74AS157D equivalent, key selection criteria include its 20 mA output drive capability, 5 V nominal supply operation, 1.3 V input threshold compatibility, and guaranteed AC performance across temperature and voltage extremes.

Technical Context

The SN74AS157D implements four independent 2:1 multiplexers sharing a common select (A/B) and strobe (G) control line. Each channel routes either input A or B to its corresponding output Y based on the logic state of A/B and G, with G acting as an active-low enable. All outputs present true (non-inverted) data.

It uses advanced Schottky (AS) bipolar technology to achieve faster switching than standard TTL or ALS variants, with typical propagation delays of 1–6 ns under 50 pF load conditions. Input thresholds (VIH = 2 V, VIL = 0.8 V) and output drive (IOH = −2 mA, IOL = 20 mA) are specified for robust noise margin and bus-driving capability in mixed-logic environments.

Key Specifications

Pinout & Package

SN74AS157D is housed in a 16-pin small-outline integrated circuit (SOIC) package with 1.27 mm pitch, 2.00 mm max height, and RoHS-compliant NiPdAu lead finish (Level-1 MSL rating).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ALS157D and SN74LS157N, the SN74AS157D provides the highest speed and strongest drive in the same 16-pin SOIC footprint-making it optimal for new designs targeting >50 MHz operation and mixed-technology interfacing.

Availability

SN74AS157D is available at Aetrix Electronics and suitable for microprocessor bus selection, digital test equipment signal routing, ALU operand multiplexing, and legacy system bus arbitration requiring stable component supply and long-term industrial availability.

Supply support for SN74AS157D 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.

The SN74AS157D belongs to TI's Advanced Schottky TTL logic family, engineered for high-speed digital systems where propagation delay, noise immunity, and TTL compatibility are critical design requirements.

FAQ

What is the maximum clock frequency supported by SN74AS157D in a multiplexed data path?

The SN74AS157D does not operate on a clock signal-it is combinatorial logic. Its usable data rate depends on propagation delay and system timing margins. With a maximum tPHL/tPLH of 11 ns (A/B → Y) and 10.5 ns (G → Y), it supports reliable operation in synchronous systems up to approximately 80 MHz when accounting for setup/hold and routing delays. The SN74AS157D is commonly deployed in 40–60 MHz bus architectures.

Does SN74AS157D support 3-state outputs?

No, the SN74AS157D does not provide 3-state (high-impedance) outputs. Its outputs are push-pull (totem-pole) and always driven to either HIGH or LOW. The strobe input (G) disables output functionality by forcing all Y outputs to a HIGH state-not high-impedance. For true 3-state operation, consider alternatives like SN74AS257 or SN74AS158 with enable-controlled tristate.

Can SN74AS157D interface directly with CMOS logic operating at 3.3 V?

The SN74AS157D is a 5 V-only device with TTL input thresholds (VIH = 2.0 V, VIL = 0.8 V), so it can accept 3.3 V CMOS HIGH signals safely. However, its outputs swing from 0.35 V (VOL) to ~3.0 V (VOH at VCC = 5 V, IOH = −2 mA), which may fall below the VIH minimum of many 3.3 V CMOS families (typically 2.0–2.33 V). A level-shifting buffer or pull-up resistor is recommended for reliable 3.3 V CMOS interfacing. The SN74AS157D itself must be powered from 5 V.

What is the power dissipation of SN74AS157D under typical operating conditions?

At VCC = 5 V and TA = 25°C, the SN74AS157D draws ICC = 17.5 mA (typical) to 28 mA (max) with all inputs driven and outputs loaded. This corresponds to 87.5 mW (typ) to 140 mW (max) static power dissipation. Dynamic power increases with switching activity but remains low due to short propagation times and absence of internal latches. Thermal design should assume 120 mW worst-case in still air for SOIC package derating.

Is SN74AS157D pin-compatible with SN74AS158?

Yes, SN74AS157D and SN74AS158 share identical pinouts, package dimensions, and electrical interfaces. The sole functional difference is output polarity: SN74AS157D provides true (non-inverted) outputs, while SN74AS158 provides inverted outputs. Both devices use the same 16-pin SOIC (D) package, same VCC/GND locations, and identical A/B/G and I/O pin assignments-enabling drop-in replacement where output inversion is acceptable or compensated in firmware/logic.