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Texas Instruments SN74LS540DWR
- Part No.:
- SN74LS540DWR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74LS540DWR.pdf
- Description:
- IC BUFFER INVERT 5.25V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:7,245
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Product details
Overview
SN74LS540DWR from Texas Instruments is an octal buffer/line driver with 3-state outputs, designed for bidirectional data bus interfacing in TTL-based 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 SN74LS540DWR datasheet, SN74LS540DWR pinout, SN74LS540DWR application, or SN74LS540DWR equivalent, this page provides verified functional specifications, SOIC-20 package details, real-world use cases, and validated alternative options for legacy TTL system design and obsolescence mitigation.
Technical Context
The SN74LS540DWR implements standard TTL-compatible input thresholds (VIL = 0.8 V, VIH = 2.0 V) and delivers rail-to-rail 3-state outputs with guaranteed high-impedance off-state leakage ≤ 10 µA. Its propagation delay is 15 ns typical at VCC = 5 V and TA = 25°C, supporting synchronous bus timing in 8-bit computing architectures.
It uses bipolar transistor-transistor logic (TTL) process technology, with internal circuitry optimized for noise immunity (VNM ≥ 0.4 V) and fan-out of 20 LS-TTL loads. The device lacks internal ESD protection diodes beyond standard junction limits and requires external clamping for hot-swap or high-noise environments.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | LS-TTL - ensures compatibility with legacy 74LS-series systems and predictable DC loading behavior |
| Function | Octal non-inverting buffer with 3-state outputs - enables bidirectional bus control via OE̅ pin |
| Supply Voltage | 4.75 V to 5.25 V - strict 5 V ±5% tolerance required for guaranteed switching and output drive |
| Output Drive | −24 mA (sink), +15 mA (source) - sufficient to drive 20 LS-TTL inputs or terminate short PCB traces |
| Propagation Delay | 15 ns max (tPLH/tPHL) - supports bus clock rates up to ~30 MHz in controlled impedance layouts |
| Operating Temperature | 0°C to 70°C - commercial-grade rating suitable for office, industrial control, and instrumentation enclosures |
| Package | SOIC-20 (DW) - 7.5 mm × 12.8 mm body, 1.27 mm pitch, RoHS-compliant NiPdAu lead finish |
Pinout & Package
SN74LS540DWR 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 8 outputs into high-impedance state when HIGH; enables buffers when LOW |
| 2–9 (A1–A8) | Inputs | Non-inverting data inputs accepting standard LS-TTL logic levels |
| 11–18 (Y1–Y8) | Outputs | 3-state buffered outputs; low-impedance HIGH/LOW when OE̅ = LOW, Hi-Z when OE̅ = HIGH |
| 10 (GND) | Ground reference | Primary signal return path; must be connected before VCC during power-up |
| 20 (VCC) | Power supply | +5 V DC supply; decoupling capacitor (0.1 µF ceramic) required within 10 mm of pin |
Key Features
| Feature | Design Value |
|---|---|
| 3-State Outputs | Enables shared-bus topology without external bus transceivers or arbitration logic |
| High Sink Current | 24 mA per output allows direct driving of LEDs, relays, or multiple LS-TTL inputs without buffering |
| Matched Propagation Delays | ≤2 ns skew between Y1–Y8 ensures simultaneous bus bit assertion for reliable parallel data transfer |
| Input Hysteresis | Typical 0.2 V threshold margin reduces susceptibility to ground bounce and crosstalk in dense layouts |
| Pin-Compatible Upgrade Path | Direct replacement for SN74LS240/LS241 in existing SOIC-20 footprints with identical pin mapping |
Applications
| Microprocessor Bus Isolation | Memory Address Latching |
|---|---|
|
Use Scenario: Isolating CPU address/data bus from peripheral expansion slots in retrocomputing or industrial PLC backplanes. IC Role / Device Role / Timing Role: Bidirectional 3-state buffer enabling time-multiplexed bus sharing between CPU and peripherals. Use Value: Prevents bus contention during DMA cycles; eliminates need for discrete bus switches or complex arbitration logic. |
Use Scenario: Driving 8-bit address lines to static RAM or EPROM chips in embedded controller subsystems. IC Role / Device Role / Timing Role: Non-inverting line driver providing robust voltage-level translation and current gain for memory address decoding. Use Value: Ensures clean, fast edge transitions across long PCB traces, reducing setup/hold timing violations at memory inputs. |
| Legacy Instrumentation I/O Expansion | TTL-Level Serial Interface Buffering |
|
Use Scenario: Adding parallel digital I/O to test equipment using aging 8085/8088-based controllers. IC Role / Device Role / Timing Role: Output latch interface between microcontroller port and external DIP-switch banks or LED arrays. Use Value: Provides galvanic separation and current amplification while maintaining LS-TTL logic compatibility and timing predictability. |
Use Scenario: Level-shifting and buffering RS-232 handshake signals (RTS/CTS/DTR) in mixed-voltage systems. IC Role / Device Role / Timing Role: Signal conditioner converting microcontroller GPIO logic levels to full TTL swing for UART control lines. Use Value: Improves noise margin and rise/fall times on long cables, reducing false handshaking errors in noisy factory environments. |
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 |
|---|---|---|---|
| SN74LS240N | Octal inverting buffer with dual-OE control (1A/2A); different truth table and pinout | Requires logic inversion in firmware/hardware; not drop-in compatible due to inverted outputs and split enable pins | Select only if system design already accommodates inverted data paths and separate enable domains |
| SN74LS541DWR | Octal non-inverting buffer with identical pinout, timing, and drive strength; differs only in output-enable polarity (active-HIGH vs. SN74LS540's active-LOW) | Requires OE signal polarity inversion in PCB routing or upstream logic; otherwise functionally identical | Preferred for new designs where active-HIGH enable simplifies control logic; same footprint and thermal profile |
Compared with SN74LS540DWR, SN74LS240N demands board-level redesign for inversion handling, while SN74LS541DWR offers identical performance with only an enable-polarity swap-making it the most seamless upgrade path for maintainable legacy systems.
Availability
SN74LS540DWR is available at Aetrix Electronics and suitable for microprocessor bus isolation, memory address latching, legacy instrumentation I/O expansion, and TTL-level serial interface buffering requiring stable component supply across extended production lifecycles.
Supply support for SN74LS540DWR 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 CMOS logic families.
SN74LS540DWR belongs to TI's legacy 74LS logic product line, engineered specifically for reliability and interoperability in industrial control, test equipment, and retrocomputing systems requiring proven, long-lifecycle components.
FAQ
What is the function of pin 1 (OE̅) on the SN74LS540DWR?
Pin 1 is the active-low output-enable (OE̅) control input. When OE̅ is LOW, the SN74LS540DWR drives its eight Y1–Y8 outputs with non-inverted copies of inputs A1–A8. When OE̅ is HIGH, all outputs enter a high-impedance (Hi-Z) state, effectively disconnecting them from the bus. This enables multi-driver bus architectures without contention.
Can SN74LS540DWR operate at 3.3 V?
No. The SN74LS540DWR is strictly a 5 V TTL device with minimum VCC = 4.75 V and maximum = 5.25 V. Operation below 4.75 V violates its input threshold specifications (VIL ≤ 0.8 V, VIH ≥ 2.0 V) and risks unreliable switching or excessive supply current. For 3.3 V systems, consider SN74LVC541A or similar LVCMOS alternatives.
Is SN74LS540DWR pin-compatible with SN74LS240?
No. Although both are octal 3-state buffers in SOIC-20 packages, SN74LS540DWR has a single active-low OE̅ (pin 1) and non-inverting outputs, whereas SN74LS240 uses dual active-low enables (pins 1 and 19) and inverting outputs (Y1–Y8). Their pin mappings differ significantly-especially for enables and output polarities-making them incompatible without PCB redesign.
What is the maximum clock frequency supported by SN74LS540DWR?
The SN74LS540DWR does not have a defined clock input; it is asynchronous. Its usable data rate depends on propagation delay (15 ns max) and system layout. In practice, it reliably supports bus toggle rates up to 30 MHz in well-terminated, low-inductance PCB environments-provided setup/hold timing margins are maintained relative to the controlling clock edge.
Does SN74LS540DWR include ESD protection?
The SN74LS540DWR incorporates basic junction-level ESD structures per standard bipolar TTL process, rated to ±2 kV HBM (Human Body Model) per JEDEC JESD22-A114. It does not feature enhanced I/O ESD clamps. For environments with frequent handling or high-static risk, external TVS diodes or series resistors are recommended-especially on bus-connected pins like Y1–Y8.
SN74LS540DWR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- 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
SN74LS540DWR FAQ
1.How can I place an order for SN74LS540DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS540DWR 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 SN74LS540DWR reliable?
The price and inventory of SN74LS540DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS540DWR is usually 5 days.
3.What payment methods are accepted for SN74LS540DWR?
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4.How is shipping managed for SN74LS540DWR?
SN74LS540DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS540DWR 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 SN74LS540DWR?
For technical support, including SN74LS540DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS540DWR requirements.
6.How does Aetrix verify that SN74LS540DWR is sourced from the original manufacturer or authorized distributors?
All SN74LS540DWR 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 SN74LS540DWR meets industry standards.
7.What is the process for return or replacement of SN74LS540DWR?
All SN74LS540DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS540DWR, 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 SN74LS540DWR part is unused and in its original packaging.
Return procedure for SN74LS540DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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