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Home > Products > Integrated Circuits (ICs) > Logic > Signal Switches, Multiplexers, Decoders

Texas Instruments SN74LS257BD

Name: SN74LS257BD
Brand: Texas Instruments
SKU: SN74LS257BD
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SN74LS257BD

Manufacturer:: Texas Instruments

Category:: Signal Switches, Multiplexers, Decoders

Package:: 16-SOIC (0.154", 3.90mm Width)

Datasheet:: SN74LS257BD.pdf

Description:: IC MULTIPLEXER 4 X 2:1 16SOIC

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Product details

Overview

SN74LS257BD from Texas Instruments is a quadruple 2-line to 1-line data selector/multiplexer in SOIC-16 package, operating over 0°C to 70°C, with TTL-compatible inputs and outputs, 15 ns typical propagation delay, and 8 mA output drive capability. It enables digital signal routing in bus management, address decoding, and logic-level data path selection.

For engineers reviewing the SN74LS257BD datasheet, SN74LS257BD pinout, SN74LS257BD application, or SN74LS257BD equivalent, key selection considerations include its quad 2:1 multiplexer architecture, TTL logic family compatibility, SOIC-16 footprint, temperature range, and direct replacement options for legacy LS-TTL system designs.

Technical Context

The SN74LS257BD implements four independent 2-input multiplexers sharing a common select (S) and output enable (G̅) control. Each channel selects between two data inputs (A and B) based on the S input state, with G̅ enabling or disabling all outputs simultaneously in active-low configuration.

It uses bipolar Schottky TTL technology, delivering guaranteed 15 ns maximum propagation delay (t_pd) at V_CC = 5 V, 25°C, with input thresholds aligned to standard TTL voltage levels (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) and output drive of –0.4 mA (I_OH) and 8 mA (I_OL) under specified load conditions.

Key Specifications

Parameter	Value and Actual Design Meaning
Function	Quadruple 2-line to 1-line data selector/multiplexer - provides four independent 2:1 switching paths in one IC.
Logic Family	TTL (Low-power Schottky) - ensures compatibility with legacy 74LS-series systems and predictable noise margins.
Propagation Delay	15 ns max (t_pd) - supports reliable operation in synchronous digital systems up to ~30 MHz clock domains.
Supply Voltage	4.75 V to 5.25 V - requires tightly regulated +5 V rail; not tolerant of wide-range or unregulated supplies.
Operating Temperature	0°C to 70°C - commercial-grade rating suitable for industrial control panels and non-military embedded equipment.
Output Drive	8 mA sink / –0.4 mA source - sufficient to drive 10 standard TTL loads or interface directly with 74LS/74ALS inputs.
Package	SOIC-16 (D), 3.9 mm body width - surface-mount compatible with standard 0.050" pitch PCB layouts and reflow assembly.

Pinout & Package

SN74LS257BD is housed in a 16-pin Small Outline Integrated Circuit (SOIC) package with 3.9 mm body width, gull-wing leads, and JEDEC MS-012AC outline. Pin 1 is marked by a beveled corner or dot; device orientation follows standard SOIC conventions with pin 1 in top-left corner when notch or marking is up.

Pin/Terminal	Circuit Role	Design Meaning
1 (G̅)	Output Enable (active low)	Disables all four Y outputs when high; required for bus isolation or power-down control.
2 (1A)	Data Input A, Channel 1	First input of first 2:1 mux; connects to primary data source when S = 0.
3 (1B)	Data Input B, Channel 1	Second input of first 2:1 mux; selected when S = 1.
4 (1Y)	Output, Channel 1	Inverted-pass-through output of Channel 1; driven only when G̅ = low.
5 (2A)	Data Input A, Channel 2	Primary input for second independent 2:1 mux.
6 (2B)	Data Input B, Channel 2	Alternate input for second mux; selected per S state.
7 (2Y)	Output, Channel 2	Non-inverting output of Channel 2; matches input logic level when enabled.
8 (GND)	Ground	Reference return for all internal circuitry and I/O; must be low-impedance connection.
9 (3Y)	Output, Channel 3	Third independent output; shares same S and G̅ controls as other channels.
10 (3B)	Data Input B, Channel 3	Secondary input for third mux; complements 3A (Pin 11).
11 (3A)	Data Input A, Channel 3	Primary input for third 2:1 mux.
12 (4A)	Data Input A, Channel 4	Primary input for fourth and final mux channel.
13 (4B)	Data Input B, Channel 4	Secondary input for fourth mux; selected when S = 1.
14 (4Y)	Output, Channel 4	Final output; completes quad functionality in single SOIC-16 footprint.
15 (S)	Select Control	Global 2:1 selection line - determines whether A or B inputs pass to all Y outputs.
16 (V_CC)	Positive Supply	+5 V DC supply; bypassing with 0.1 µF ceramic capacitor near pin is mandatory for stable operation.

Key Features

Feature	Design Value
Quad 2:1 multiplexer function	Integrates four independent data selectors in one SOIC-16 package, reducing board space vs discrete solutions.
Active-low output enable (G̅)	Allows simultaneous disable of all outputs for bus contention avoidance or power gating in multi-device systems.
TTL-compatible input thresholds	V_IL ≤ 0.8 V and V_IH ≥ 2.0 V ensure robust interfacing with standard 74LS, 74ALS, and microcontroller GPIOs.
15 ns max propagation delay	Enables use in timing-critical applications such as address/data bus steering in 8-bit microprocessor systems (e.g., Z80, 8080).
SOIC-16 surface-mount package	Supports automated assembly and higher board density than through-hole PDIP variants while maintaining pin compatibility.

Applications

Microprocessor Bus Steering	Industrial Logic Control Panel
Use Scenario: Routing address or data lines between CPU, memory, and peripheral ICs in an 8-bit embedded controller system. IC Role / Device Role / Timing Role: Data selector that dynamically switches between alternate memory banks or I/O port mappings under software control via S and G̅. Use Value: Eliminates need for discrete gates or jumpers; enables flexible memory expansion and peripheral arbitration without hardware changes.	Use Scenario: Implementing manual/auto mode selection in PLC-based machine control cabinets with dual sensor inputs. IC Role / Device Role / Timing Role: Multiplexer selecting between operator panel DIP-switch settings (A inputs) and auto-mode register values (B inputs) for real-time control logic. Use Value: Provides deterministic, glitch-free signal routing during mode transitions due to synchronized S/G̅ control and TTL noise immunity.
Digital Test Equipment Signal Routing	Legacy Instrumentation Data Path Switching
Use Scenario: Configurable signal path selection in benchtop logic analyzers or pattern generators with multiple input sources. IC Role / Device Role / Timing Role: Quad 2:1 switch enabling user-selectable routing of test signals to measurement front-ends or stimulus outputs. Use Value: Delivers consistent 15 ns propagation across all four channels, ensuring precise timing alignment in high-speed digital test setups.	Use Scenario: Replacing failed multiplexers in discontinued medical or aerospace instrumentation requiring long-term component availability. IC Role / Device Role / Timing Role: Drop-in functional replacement for obsolete 74LS257 variants in repair and sustainment programs. Use Value: Maintains identical pinout, timing, and drive strength as original design, avoiding PCB redesign or firmware modification.

Microprocessor Bus Steering

Industrial Logic Control Panel

Use Scenario: Routing address or data lines between CPU, memory, and peripheral ICs in an 8-bit embedded controller system.

IC Role / Device Role / Timing Role: Data selector that dynamically switches between alternate memory banks or I/O port mappings under software control via S and G̅.

Use Value: Eliminates need for discrete gates or jumpers; enables flexible memory expansion and peripheral arbitration without hardware changes.

Use Scenario: Implementing manual/auto mode selection in PLC-based machine control cabinets with dual sensor inputs.

IC Role / Device Role / Timing Role: Multiplexer selecting between operator panel DIP-switch settings (A inputs) and auto-mode register values (B inputs) for real-time control logic.

Use Value: Provides deterministic, glitch-free signal routing during mode transitions due to synchronized S/G̅ control and TTL noise immunity.

Digital Test Equipment Signal Routing

Legacy Instrumentation Data Path Switching

Use Scenario: Configurable signal path selection in benchtop logic analyzers or pattern generators with multiple input sources.

IC Role / Device Role / Timing Role: Quad 2:1 switch enabling user-selectable routing of test signals to measurement front-ends or stimulus outputs.

Use Value: Delivers consistent 15 ns propagation across all four channels, ensuring precise timing alignment in high-speed digital test setups.

Use Scenario: Replacing failed multiplexers in discontinued medical or aerospace instrumentation requiring long-term component availability.

IC Role / Device Role / Timing Role: Drop-in functional replacement for obsolete 74LS257 variants in repair and sustainment programs.

Use Value: Maintains identical pinout, timing, and drive strength as original design, avoiding PCB redesign or firmware modification.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
SN74LS257BN	Same logic function and electrical specs, but in 16-pin PDIP (through-hole) package with 0°C to 70°C rating.	Suitable for prototyping, hand-soldered assemblies, or legacy through-hole production lines.	Choose SN74LS257BN if board layout uses DIP footprints or manual assembly is required.
SN74LS257BDR	Identical SOIC-16 package and specs, but active production status and RoHS-compliant NiPdAu lead finish (vs obsolete SN74LS257BD).	Designed for new production runs requiring current TI part numbers and modern environmental compliance.	Prefer SN74LS257BDR for volume manufacturing where supply continuity and RoHS conformance are mandatory.

Compared with SN74LS257BD, SN74LS257BN offers mechanical compatibility with breadboards and sockets but lacks surface-mount efficiency, while SN74LS257BDR delivers identical performance with assured long-term availability, RoHS compliance, and optimized reflow profile support.

Availability

SN74LS257BD is available at Aetrix Electronics and suitable for industrial control panels, legacy instrumentation repair, and microprocessor bus management requiring stable component supply and known LS-TTL timing behavior.

Supply support for SN74LS257BD 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, embedded processing, and logic ICs with broad industrial, automotive, and consumer applications.

The SN74LS257BD belongs to TI's classic 74LS logic family, designed specifically for reliable, low-power digital signal routing in commercial-grade systems where TTL compatibility and predictable propagation delay are critical.

FAQ

What is the operating voltage range for SN74LS257BD?

The SN74LS257BD operates within a strict 4.75 V to 5.25 V supply range. Operation outside this window risks incorrect logic states or increased propagation delay. This narrow tolerance reflects its bipolar Schottky TTL design and mandates use with a well-regulated +5 V rail - not suitable for battery-powered or wide-input-voltage applications.

Is SN74LS257BD pin-compatible with SN74LS257BN?

Yes, SN74LS257BD and SN74LS257BN share identical pin assignments and electrical specifications. The only difference is package type: SN74LS257BD uses SOIC-16 (surface-mount), while SN74LS257BN uses PDIP-16 (through-hole). No schematic or logic change is needed when substituting between them, though PCB layout and assembly process differ.

Does SN74LS257BD support hot-swapping or live insertion?

No, SN74LS257BD does not support hot-swapping. Its TTL input structure lacks protection against back-driving or voltage transients during insertion. Applying power or signals before full mechanical seating may cause latch-up or permanent damage. Always power-cycle the system before inserting or removing the SN74LS257BD.

What is the maximum clock frequency supported by SN74LS257BD?

The SN74LS257BD does not operate on a clock; it is a combinational logic device. Its usable data rate depends on propagation delay (15 ns max) and system setup/hold timing. In practice, it reliably supports asynchronous data switching up to ~30 MHz in well-designed PCB layouts with controlled trace lengths and proper decoupling.

Can SN74LS257BD drive LED indicators directly?

Yes, SN74LS257BD can drive standard 5 mm LEDs directly when configured as a current sink (using Y outputs with cathode-to-output, anode-to-V_CC via current-limiting resistor). Its 8 mA output sink capability supports typical 2–5 mA LED currents. Do not attempt source-driving (anode-to-output) - its 0.4 mA source drive is insufficient for most indicator LEDs.

SN74LS257BD Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: 74LS

Package/Case:: 16-SOIC (0.154", 3.90mm Width)

Packaging:: Tube

Product Status:: Obsolete

Type:: Multiplexer

Circuit:: 4 x 2:1

Independent Circuits:: 1

Current - Output High, Low:: 2.6mA, 24mA

Voltage Supply Source:: Single Supply

Voltage - Supply:: 4.75V ~ 5.25V

Operating Temperature:: 0°C ~ 70°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 16-SOIC

SN74LS257BD FAQ

1.How can I place an order for SN74LS257BD through Aetrix?

Please submit a Request for Quotation (RFQ) for SN74LS257BD on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for SN74LS257BD reliable?

The price and inventory of SN74LS257BD are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS257BD is usually 5 days.

3.What payment methods are accepted for SN74LS257BD?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS257BD transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SN74LS257BD?

SN74LS257BD orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SN74LS257BD order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for SN74LS257BD?

For technical support, including SN74LS257BD datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS257BD requirements.

6.How does Aetrix verify that SN74LS257BD is sourced from the original manufacturer or authorized distributors?

All SN74LS257BD products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74LS257BD meets industry standards.

7.What is the process for return or replacement of SN74LS257BD?

All SN74LS257BD units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS257BD, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The SN74LS257BD part is unused and in its original packaging.

Return procedure for SN74LS257BD:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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