Texas Instruments SN74LS157N

Overview

SN74LS157N from Texas Instruments is a quad 2-input data selector/multiplexer in a 16-pin PDIP package, operating from 4.75 V to 5.25 V with typical propagation delay of 15 ns and fan-out capability of 20 LS-TTL loads. It performs logic-level signal routing in digital control systems, enabling selection between two 4-bit data buses under a single select line - commonly used in address/data bus switching in legacy microprocessor interfaces.

For engineers reviewing the SN74LS157N datasheet, SN74LS157N pinout, SN74LS157N application, or SN74LS157N equivalent, key selection criteria include its TTL-compatible input thresholds, guaranteed output drive strength at V_CC = 5 V, temperature range (0 °C to 70 °C), and compatibility with standard LS-TTL logic families in industrial control and test equipment designs.

Technical Context

The SN74LS157N implements four independent 2:1 multiplexers sharing a common strobe (G̅) and select (S) control. Each channel routes either A or B input to Y output based on S state, with active-low enable G̅ overriding selection. Its bipolar TTL architecture ensures predictable noise margins and deterministic timing across the full commercial temperature range.

All outputs are buffered with totem-pole drivers capable of sourcing 0.4 mA and sinking 8 mA at V_CC = 5 V, supporting direct interfacing with other LS-TTL devices without external pull-ups. Input clamp diodes provide ESD protection, and internal circuitry guarantees monotonic switching behavior during select transitions.

Key Specifications

Pinout & Package

SN74LS157N uses a 16-pin plastic dual in-line package (PDIP-N), 0.3-inch body width, with standard through-hole mounting and 0.1-inch pin pitch. Package height is 4.57 mm max, and lead finish is matte tin (NIPDAU).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS157N, SN74LS158N delivers inverted outputs without added delay but limits direct replacement in non-inverting paths, while SN74LS257N adds bus-hold capability and three-state control - making it suitable for dynamic bus arbitration but requiring updated receiver design.

Availability

SN74LS157N is available at Aetrix Electronics and suitable for industrial control panels, legacy test instrumentation, and educational electronics kits requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS157N 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 company founded in 1930, specializing in analog and embedded processing technologies with broad portfolio coverage across industrial, automotive, and consumer markets.

The SN74LS157N belongs to TI's legacy 74LS logic family, designed specifically for reliable, low-cost digital signal routing in commercial-grade systems where interoperability with established TTL infrastructure is essential.

FAQ

What is the maximum clock frequency supported by SN74LS157N?

The SN74LS157N does not operate on a clock signal - it is a combinational logic device whose output responds asynchronously to input and select changes. Its usable data rate is limited by propagation delay (15 ns max), meaning it can reliably steer signals with transition periods longer than ~30 ns. For SN74LS157N, this corresponds to effective toggle rates below 33 MHz in edge-triggered contexts, though actual system timing depends on setup/hold margins of connected devices.

Can SN74LS157N be used with 3.3 V logic systems?

No - SN74LS157N requires a 4.75 V to 5.25 V supply and is not 3.3 V tolerant. Its inputs expect LS-TTL voltage thresholds (V_IH ≥ 2.0 V), and applying 3.3 V logic levels may result in marginal or unreliable recognition of high states. Direct interfacing with 3.3 V systems requires level-shifting circuitry or substitution with a 3.3 V–compatible multiplexer such as the SN74LVC157A. The SN74LS157N is strictly a 5 V device.

Does SN74LS157N have built-in ESD protection?

Yes - SN74LS157N includes integrated input clamp diodes rated for ±10 mA transient current, providing basic ESD immunity per MIL-STD-883 Class 3B (2 kV HBM). This protection is sufficient for handling typical handling-induced discharges in controlled environments but does not replace system-level TVS or RC filtering in high-noise industrial settings. No external protection is required for standard bench use, but SN74LS157N should not be exposed to uncontrolled ESD events exceeding specification limits.

Is SN74LS157N pin-compatible with CMOS equivalents like CD4052?

No - SN74LS157N and CD4052 are not pin-compatible. SN74LS157N uses a 16-pin PDIP layout with dedicated A/B inputs, Y outputs, G̅, and S pins, whereas CD4052 is an 8-channel analog multiplexer in a 16-pin package with different pin assignments (e.g., INH, A0/A1 address lines, Z outputs). Their logic families, supply ranges, and functional architectures differ fundamentally. Substituting CD4052 for SN74LS157N would require PCB redesign and signal conditioning.

What is the power dissipation of SN74LS157N under typical operating conditions?

SN74LS157N dissipates approximately 48 mW per device at V_CC = 5 V and 25 °C with all outputs loaded - calculated from typical supply current (I_CC) of 19 mA and V_CC. Power increases with switching activity and output loading; worst-case (all outputs sinking 8 mA) reaches ~85 mW. Thermal derating is not required below 70 °C ambient, and no heatsinking is needed in standard through-hole layouts. This makes SN74LS157N suitable for dense logic arrays where thermal management is constrained.