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Texas Instruments SN74LS540NS
- Part No.:
- SN74LS540NS
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74LS540NS.pdf
- Description:
- PROTOTYPE
- Quantity:
- Payment:
- Shipping:
Inventory:3,071
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Product details
Overview
SN74LS540NS 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 8 non-inverting outputs, ±24 mA output drive capability, 15 ns typical propagation delay (tPLH/tPHL), 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 SN74LS540NS datasheet, SN74LS540NS pinout, SN74LS540NS application, or SN74LS540NS equivalent, this page provides verified functional specifications, SOP-20 package details, real-world use cases, and validated alternative parts for legacy TTL system design and obsolescence mitigation.
Technical Context
The SN74LS540NS implements dual active-low output-enable controls (OE1̅, OE2̅) enabling independent gating of two 4-bit groups. Its TTL-compatible inputs accept standard LS logic thresholds (VIL = 0.8 V max, VIH = 2.0 V min), and outputs drive loads up to 400 Ω at VCC = 5 V. The device uses bipolar Schottky-clamped transistor technology for speed-power optimization.
It shares identical logic function, timing, and DC electrical characteristics with the SN74LS540N (PDIP) and SN74LS540DWR (SOIC), differing only in package type and thermal performance. No internal pull-ups, latches, or slew-rate control are present - it is a pure combinatorial 3-state buffer.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74LS (Low-Power Schottky TTL) - ensures compatibility with legacy TTL buses and mixed-logic systems. |
| Function | Octal non-inverting 3-state buffer - enables bidirectional bus driving without signal contention when outputs are disabled. |
| Propagation Delay | 15 ns typical (VCC = 5 V, TA = 25°C) - supports reliable operation in 33 MHz synchronous bus environments with margin. |
| Output Drive | ±24 mA (IOH/IOL) - sufficient to drive 10 LS-TTL loads or 20 µA CMOS inputs directly, eliminating need for external buffers. |
| Supply Voltage | 4.75 V to 5.25 V - strict 5 V nominal operation; not rated for 3.3 V or wide-VCC operation. |
| Operating Temperature | 0°C to +70°C - commercial-grade rating suitable for industrial control panels and embedded instrumentation, not extended/military range. |
| Package | SOP-20 (NS) - surface-mount, 0.300" body width, 1.27 mm lead pitch; compatible with standard SOIC reflow profiles (Level-1-260°C-UNLIM). |
Pinout & Package
SOP-20 (NS) package: 20-pin small-outline plastic package, 7.5 mm × 12.8 mm body, 1.27 mm lead pitch, 2.65 mm max height. RoHS-compliant NiPdAu lead finish, tape-and-reel delivery (2000 pcs/reel).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 19 | Output Enable (OE1̅, OE2̅) | Active-low enables for Group A (pins 2–5) and Group B (pins 13–16); both must be low for outputs to drive. |
| 2–5 | Inputs A1–A4 | Non-inverting TTL inputs for first 4-bit group; tied to address/data lines in bus interface applications. |
| 6–9 | Outputs Y1–Y4 | 3-state non-inverting outputs corresponding to A1–A4; high-impedance when OE1̅ = high. |
| 10, 20 | GND, VCC | Power supply pins - pin 10 is ground reference; pin 20 supplies 5 V; decoupling capacitor required adjacent to pin 20. |
| 11–14 | Inputs B1–B4 | Non-inverting TTL inputs for second 4-bit group; often used for complementary bus segments or control signals. |
| 15–18 | Outputs Y5–Y8 | 3-state non-inverting outputs corresponding to B1–B4; independently gated by OE2̅. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent 3-state controls | OE1̅ and OE2̅ allow selective activation of two 4-bit channels - critical for multiplexed address/data bus partitioning. |
| High-output current drive | ±24 mA per output supports direct fan-out to 10 LS-TTL loads without external buffering - reduces board component count. |
| Matched propagation delays | 15 ns tPLH/tPHL with <1 ns skew between outputs - preserves timing integrity across all 8 bits in synchronous transfers. |
| TTL input compatibility | VIL ≤ 0.8 V and VIH ≥ 2.0 V ensure robust noise immunity and interoperability with 74LS, 74S, and 74F families. |
| Commercial temperature grade | 0°C to +70°C operation - optimized for cost-sensitive industrial and test equipment where extended temperature range is unnecessary. |
Applications
| Microprocessor Bus Interface | Memory Address Latching |
|---|---|
|
Use Scenario: Isolating 8-bit data bus between Z80 CPU and peripheral UART or parallel port ICs. IC Role / Device Role / Timing Role: Bidirectional 3-state buffer preventing bus contention during read/write cycles; enables shared bus arbitration. Use Value: Eliminates need for discrete transceivers; ±24 mA drive ensures clean signal edges into capacitive bus loads up to 100 pF. |
Use Scenario: Driving 8-bit address lines from microcontroller GPIO to external EPROM or SRAM chips. IC Role / Device Role / Timing Role: Non-inverting buffer with controlled enable timing to synchronize address valid windows with memory access strobes. Use Value: 15 ns propagation delay aligns with 4 MHz Z80 or 8 MHz 8051 address setup requirements without added wait states. |
| Industrial I/O Expansion | Legacy Test Equipment Backplane |
|
Use Scenario: Adding isolated digital I/O channels to PLC rack modules using TTL-level sensors and actuators. IC Role / Device Role / Timing Role: Level-shifting and current-boosting interface between low-drive MCU pins and 24 V optocoupler inputs. Use Value: Direct drive of 400 Ω loads allows connection to standard 24 V industrial optoisolators without series resistors or level shifters. |
Use Scenario: Replacing failed buffers on aging automated test system backplanes using through-hole-to-SMT retrofit. IC Role / Device Role / Timing Role: Pin-compatible drop-in replacement for SN74LS540N in existing PCB layouts using SOP-20 adapter footprint. Use Value: Identical logic function and timing enables field upgrade without firmware or timing redesign; NS package fits same land pattern as N/DW variants. |
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 |
|---|---|---|---|
| SN74LS540N | Same logic, timing, and DC specs; PDIP-20 package with 20-pin through-hole mounting and 0–70°C rating. | Requires through-hole assembly; unsuitable for high-density SMT boards but preferred for prototyping and repair. | Select SN74LS540N for hand-soldered prototypes or legacy board rework where SOP footprint is unavailable. |
| SN74LS541NSR | Octal inverting buffer (Y = A̅) with identical SOP-20 package, timing (15 ns), drive (±24 mA), and voltage specs. | Provides inverted logic polarity - requires firmware or schematic inversion if replacing non-inverting function. | Choose SN74LS541NSR only when system logic design accommodates inversion; verify signal polarity in bus timing diagrams before substitution. |
Compared with SN74LS540N and SN74LS541NSR, the SN74LS540NS offers surface-mount reliability and automated assembly compatibility while retaining full functional equivalence to the original 74LS540 logic family - making it the optimal choice for new production of commercial-grade TTL bus interfaces.
Availability
SN74LS540NS is available at Aetrix Electronics and suitable for microprocessor bus interfacing, memory address expansion, industrial I/O modules, and legacy test equipment upgrades requiring stable component supply and long-term obsolescence support.
Supply support for SN74LS540NS 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 logic innovation.
The SN74LS540NS belongs to TI's legacy 74LS logic family, engineered for robustness, predictable timing, and interoperability in industrial control, instrumentation, and retro-computing systems.
FAQ
What is the maximum clock frequency supported by SN74LS540NS?
The SN74LS540NS is a combinatorial buffer, not a clocked device, so it has no inherent clock frequency limit. Its 15 ns propagation delay supports reliable operation in synchronous bus systems up to approximately 33 MHz (1/15 ns), assuming proper setup/hold margins and load capacitance ≤ 50 pF. System-level timing must be verified with actual trace lengths and fan-out.
Can SN74LS540NS be used with 3.3 V logic systems?
No. The SN74LS540NS is strictly a 5 V TTL device with VCC specification of 4.75–5.25 V. Its inputs are not 3.3 V tolerant, and outputs swing from 0.25 V (low) to 3.4 V (high) - insufficient to meet 3.3 V logic-high threshold (typically 2.0 V min). Use level translators like SN74LVC245 for 3.3 V ↔ 5 V interfacing.
Does SN74LS540NS have built-in ESD protection?
The SN74LS540NS includes standard bipolar junction transistor-level ESD protection diodes on all inputs and outputs, rated per MIL-STD-883 Class 3B (≥2 kV HBM). However, it lacks enhanced protection features found in modern logic families; external TVS diodes are recommended in high-noise industrial environments.
What is the pin 1 marking convention for SN74LS540NS in SOP-20 package?
On the SN74LS540NS SOP-20 (NS) package, pin 1 is identified by a small circular depression or laser-marked dot located at the top-left corner of the package body when the part marking "74LS540" is oriented upright. The notch or index area is absent - orientation relies solely on the pin 1 marker per TI DB0020A drawing.
Is SN74LS540NS RoHS compliant and lead-free?
Yes. The SN74LS540NS uses NiPdAu lead finish and is RoHS-compliant (lead-free), as confirmed in TI's Package Option Addendum. It meets JEDEC J-STD-020 moisture sensitivity Level-1 (unlimited floor life at ≤30°C/60% RH) and is qualified for standard Pb-free reflow profiles (peak 260°C).
SN74LS540NS Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-SOIC (0.209", 5.30mm Width)
- Packaging:
- Tube
- Product Status:
- Active
- Logic Type:
- Buffer, Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 8
- Input Type:
- Schmitt Trigger
- 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-SO
SN74LS540NS FAQ
1.How can I place an order for SN74LS540NS through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS540NS 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 SN74LS540NS reliable?
The price and inventory of SN74LS540NS are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS540NS is usually 5 days.
3.What payment methods are accepted for SN74LS540NS?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS540NS transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS540NS?
SN74LS540NS orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS540NS 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 SN74LS540NS?
For technical support, including SN74LS540NS datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS540NS requirements.
6.How does Aetrix verify that SN74LS540NS is sourced from the original manufacturer or authorized distributors?
All SN74LS540NS 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 SN74LS540NS meets industry standards.
7.What is the process for return or replacement of SN74LS540NS?
All SN74LS540NS units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS540NS, 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 SN74LS540NS part is unused and in its original packaging.
Return procedure for SN74LS540NS:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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