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Home > Products > Integrated Circuits (ICs) > Logic > Buffers, Drivers, Receivers, Transceivers

Texas Instruments SN74LS540DW

Name: SN74LS540DW
Brand: Texas Instruments
SKU: SN74LS540DW
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SN74LS540DW

Manufacturer:: Texas Instruments

Category:: Buffers, Drivers, Receivers, Transceivers

Package:: 20-SOIC (0.295", 7.50mm Width)

Datasheet:: SN74LS540DW.pdf

Description:: IC BUFFER INVERT 5.25V 20SOIC

Quantity:: RFQ Add To RFQ list

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Product details

Overview

SN74LS540DW from Texas Instruments is an octal buffer/line driver with 3-state outputs, designed for bidirectional data bus interfacing in TTL-based digital systems. It features active-low output-enable (OE̅), 8-bit non-inverting logic, ±24 mA output drive capability, and operates over 0°C to 70°C. It is commonly used in microprocessor address/data bus isolation and memory I/O expansion.

For engineers reviewing the SN74LS540DW datasheet, SN74LS540DW pinout, SN74LS540DW application, or SN74LS540DW equivalent, this page delivers verified electrical parameters, SOIC-20 package details, functional role in bus buffering, and validated alternative options for legacy TTL system design and obsolescence mitigation.

Technical Context

The SN74LS540DW implements eight independent non-inverting buffers, each with a common active-low 3-state output-enable control (pin 1). Its TTL-compatible inputs accept standard LS logic thresholds, and outputs drive ±24 mA at V_CC = 5 V, enabling direct interface with other 74LS, 74S, and 74F family devices. Propagation delay is 15 ns typical (A→Y) under loaded conditions.

It uses bipolar transistor–transistor logic (TTL) with Schottky-clamped inputs and outputs, ensuring noise immunity and stable switching across its specified temperature range. The device lacks internal clamping diodes or ESD protection beyond standard process-level robustness, requiring external transient suppression in noisy industrial environments.

Key Specifications

Parameter	Value and Actual Design Meaning
Logic Family	74LS TTL - ensures compatibility with legacy LS/S/F-series logic and predictable DC noise margins.
Function	Octal non-inverting 3-state buffer - provides bidirectional bus control via single OE̅ input.
Supply Voltage	4.75 V to 5.25 V - requires tightly regulated +5 V rail; not tolerant of wider voltage swings.
Output Drive	±24 mA (I_OH/I_OL) - sufficient to drive 15 LS loads or one S-load without fanout limitation.
Propagation Delay	15 ns max (A to Y, V_CC = 5 V, C_L = 15 pF) - defines maximum clock/data rate for synchronous bus timing.
Operating Temperature	0°C to +70°C - commercial-grade rating; unsuitable for extended industrial or automotive ambient ranges.
Package	SOIC-20 (DW) - 7.5 mm × 12.8 mm body, 1.27 mm pitch, surface-mount compatible with standard reflow profiles.

Pinout & Package

SN74LS540DW is housed in a 20-pin small-outline integrated circuit (SOIC) package (DW), measuring 7.5 mm × 12.8 mm with 1.27 mm lead pitch and 2.65 mm maximum height. Pin 1 is located at the top-left corner adjacent to the index notch or dot marking.

Pin/Terminal	Circuit Role	Design Meaning
1 (OE̅)	Active-low output enable	Drives all eight outputs into high-impedance state when HIGH; enables buffers when LOW.
2–9 (A1–A8)	Input signals	Non-inverting data inputs accepting standard TTL voltage levels (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V).
11–18 (Y1–Y8)	3-state buffered outputs	Drive outputs actively HIGH/LOW or float (high-Z) based on OE̅; support wired-OR bus sharing.
10 (GND)	Ground reference	Primary signal return path; must be low-inductance connection to minimize ground bounce.
20 (V_CC)	Positive supply	+5 V power rail; requires local 0.1 µF ceramic decoupling capacitor placed within 5 mm.

Key Features

Feature	Design Value
Octal non-inverting 3-state architecture	Enables single-directional data flow control on shared buses without direction pins or external logic.
±24 mA output sink/source capability	Eliminates need for external bus transceivers in moderate-fanout LS-system designs.
TTL-compatible input thresholds	Guarantees interoperability with 74LS, 74S, and 74F families without level-shifting circuitry.
15 ns typical propagation delay	Supports reliable operation up to ~30 MHz bus toggle rates in properly terminated layouts.
SOIC-20 RoHS-compliant packaging	Enables automated assembly using standard pick-and-place and reflow processes (MSL Level-1).

Applications

Microprocessor Bus Interface	Memory Address Latching
Use Scenario: Isolating CPU address/data lines from peripheral ICs during DMA or interrupt cycles. IC Role / Device Role / Timing Role: Bidirectional 3-state buffer controlling data flow direction and preventing bus contention. Use Value: Prevents signal corruption by disabling outputs during bus arbitration, leveraging OE̅ for precise timing-aligned gating.	Use Scenario: Holding stable address bits for static RAM or EPROM access while CPU executes other instructions. IC Role / Device Role / Timing Role: Non-inverting latch-enabling buffer that presents clean, low-skew address signals to memory chips. Use Value: Ensures address setup/hold times are met with minimal propagation delay and full TTL drive strength.
Legacy Industrial Controller I/O Expansion	Test Equipment Signal Conditioning
Use Scenario: Adding parallel I/O ports to PLC backplanes using existing 5 V TTL infrastructure. IC Role / Device Role / Timing Role: Level-shifting and fanout-multiplying buffer between controller ASIC and discrete I/O modules. Use Value: Delivers robust ±24 mA drive to drive long PCB traces and multiple LED indicators or optocouplers.	Use Scenario: Conditioning digital stimulus signals before injection into DUTs during ATE testing. IC Role / Device Role / Timing Role: Signal integrity-preserving buffer isolating pattern generator outputs from variable DUT input capacitance. Use Value: Maintains fast edge rates (15 ns delay) and prevents source loading, improving test repeatability and timing margin.

Microprocessor Bus Interface

Memory Address Latching

Use Scenario: Isolating CPU address/data lines from peripheral ICs during DMA or interrupt cycles.

IC Role / Device Role / Timing Role: Bidirectional 3-state buffer controlling data flow direction and preventing bus contention.

Use Value: Prevents signal corruption by disabling outputs during bus arbitration, leveraging OE̅ for precise timing-aligned gating.

Use Scenario: Holding stable address bits for static RAM or EPROM access while CPU executes other instructions.

IC Role / Device Role / Timing Role: Non-inverting latch-enabling buffer that presents clean, low-skew address signals to memory chips.

Use Value: Ensures address setup/hold times are met with minimal propagation delay and full TTL drive strength.

Legacy Industrial Controller I/O Expansion

Test Equipment Signal Conditioning

Use Scenario: Adding parallel I/O ports to PLC backplanes using existing 5 V TTL infrastructure.

IC Role / Device Role / Timing Role: Level-shifting and fanout-multiplying buffer between controller ASIC and discrete I/O modules.

Use Value: Delivers robust ±24 mA drive to drive long PCB traces and multiple LED indicators or optocouplers.

Use Scenario: Conditioning digital stimulus signals before injection into DUTs during ATE testing.

IC Role / Device Role / Timing Role: Signal integrity-preserving buffer isolating pattern generator outputs from variable DUT input capacitance.

Use Value: Maintains fast edge rates (15 ns delay) and prevents source loading, improving test repeatability and timing margin.

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal 3-state buffer applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
SN74LS541DW	Inverting output logic (Y = A̅); identical pinout, timing, and drive specs.	Requires logic inversion in upstream/downstream logic; unsuitable where signal polarity must be preserved.	Select only if system-level inversion is acceptable or already compensated elsewhere in the data path.
SN74HC240N	CMOS technology (74HC), 2 V–6 V supply, lower I_CC, but only ±4 mA drive at 5 V.	Higher noise immunity and lower power, but insufficient drive for legacy LS bus loads without pull-ups or buffers.	Prefer for new low-power designs with HC-compatible interfaces; avoid in mixed-LS-bus systems requiring ±24 mA.

Compared with SN74LS541DW, SN74LS540DW preserves signal polarity critical for address/data integrity; versus SN74HC240N, it delivers proven ±24 mA drive essential for maintaining noise margins and fanout in established TTL infrastructures.

Availability

SN74LS540DW is available at Aetrix Electronics and suitable for microprocessor bus interface, memory address latching, legacy industrial controller I/O expansion, and test equipment signal conditioning requiring stable component supply across long-lifecycle embedded programs.

Supply support for SN74LS540DW 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 with deep heritage in TTL and standard logic families.

The SN74LS540DW belongs to TI's 74LS logic portfolio, engineered for reliability and interoperability in industrial control, instrumentation, and legacy computing systems requiring deterministic TTL timing and robust bus driving.

FAQ

What is the function of pin 1 on the SN74LS540DW?

Pin 1 on the SN74LS540DW is the active-low output-enable (OE̅) input. When held LOW, all eight outputs (Y1–Y8) are enabled and follow their respective inputs (A1–A8) with non-inverting logic. When driven HIGH, all outputs enter high-impedance (3-state) mode, effectively disconnecting them from the bus. This enables shared-bus architectures without contention.

Does the SN74LS540DW support mixed-voltage operation?

No, the SN74LS540DW is strictly a 5 V TTL device with a recommended supply range of 4.75 V to 5.25 V. It does not support operation below 4.75 V or above 5.25 V, and has no multi-voltage I/O capability. Interfacing with 3.3 V or 2.5 V logic requires level-shifting circuitry or compatible translators.

Can SN74LS540DW replace SN74LS240 in a design?

No - SN74LS240 is an inverting octal buffer (Y = A̅), whereas SN74LS540DW is non-inverting (Y = A). Though pin-compatible and electrically similar, the logic polarity difference makes them functionally incompatible without redesigning upstream/downstream logic to compensate for inversion.

What is the maximum capacitive load the SN74LS540DW can drive reliably?

The SN74LS540DW is characterized for a 15 pF capacitive load in timing specifications (e.g., 15 ns propagation delay). While it can drive higher capacitance due to its ±24 mA output capability, exceeding 40–50 pF may degrade edge rates and increase propagation delay beyond specification limits, risking timing violations in high-speed bus applications.

Is SN74LS540DW RoHS compliant?

Yes, the SN74LS540DW (orderable part number SN74LS540DWR.A) is RoHS compliant, with lead finish NIPDAU (Nickel/Palladium/Gold) and MSL Level-1 rating for unlimited floor life at ≤30°C/60% RH. It meets JEDEC J-STD-020 requirements for lead-free reflow soldering at 260°C peak.

SN74LS540DW Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: 74LS

Package/Case:: 20-SOIC (0.295", 7.50mm Width)

Packaging:: Tube

Product Status:: Obsolete

Logic Type:: Buffer, Inverting

Number of Elements:: 1

Number of Bits per Element:: 8

Input Type:: -

Output Type:: 3-State

Current - Output High, Low:: 15mA, 24mA

Voltage - Supply:: 4.75V ~ 5.25V

Operating Temperature:: 0°C ~ 70°C (TA)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 20-SOIC

SN74LS540DW FAQ

1.How can I place an order for SN74LS540DW through Aetrix?

Please submit a Request for Quotation (RFQ) for SN74LS540DW 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 SN74LS540DW reliable?

The price and inventory of SN74LS540DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS540DW is usually 5 days.

3.What payment methods are accepted for SN74LS540DW?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS540DW transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SN74LS540DW?

SN74LS540DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SN74LS540DW 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 SN74LS540DW?

For technical support, including SN74LS540DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS540DW requirements.

6.How does Aetrix verify that SN74LS540DW is sourced from the original manufacturer or authorized distributors?

All SN74LS540DW 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 SN74LS540DW meets industry standards.

7.What is the process for return or replacement of SN74LS540DW?

All SN74LS540DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS540DW, 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 SN74LS540DW part is unused and in its original packaging.

Return procedure for SN74LS540DW:

1.Submit a request within 90 days.

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

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