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Texas Instruments SN74ALS540DWR
- Part No.:
- SN74ALS540DWR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS540DWR.pdf
- Description:
- IC BUFFER INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,442
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Product details
Overview
SN74ALS540DWR from Texas Instruments is an octal inverting buffer/line driver with 3-state outputs, designed for bus interfacing and memory address register buffering in TTL-compatible digital systems. It features dual 3-state enable inputs (OE1/OE2), pnp input structure for reduced DC loading, and a data flowthrough pinout (inputs on one side, outputs on the other) to simplify PCB layout. Operating at 4.5–5.5 V, it delivers 24 mA low-level output drive and supports propagation delays as low as 2 ns.
For engineers reviewing the SN74ALS540DWR datasheet, SN74ALS540DWR pinout, SN74ALS540DWR application, or SN74ALS540DWR equivalent, key selection criteria include its inverted logic function, 20-pin SOIC-DW package thermal performance (θJA = 58°C/W), 3-state timing parameters (tPZL ≤ 20 ns, tPHZ ≤ 10 ns), and compatibility with legacy ALS-family bus architectures requiring high noise immunity and controlled output disable behavior.
Technical Context
This device implements a dual-NOR 3-state control gate: either OE1 or OE2 high forces all eight Y outputs into high-impedance mode, enabling shared-bus arbitration. Its pnp input stage lowers input current draw versus standard TTL, reducing loading on upstream drivers.
The SN74ALS540 provides true-inverted data path (A→Y inversion), distinguishing it from the non-inverting SN74ALS541. The DW package variant uses a 20-pin SOIC footprint with 1.27 mm pitch, 7.5 mm width, and 2.65 mm max height per JEDEC MS-013, supporting surface-mount assembly with MSL Level-1 reflow profile.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - Ensures compatibility with standard 5 V TTL power rails and tolerates supply ripple without functional degradation. |
| IOL (max) | 24 mA - Supports driving heavy capacitive loads (e.g., long traces or multiple TTL inputs) while maintaining VOL ≤ 0.4 V. |
| tPLH / tPHL | 2 ns to 12 ns - Enables reliable operation in high-speed address/data bus applications up to ~50 MHz clock domains. |
| IOZH / IOZL | ±20 µA - Confirms minimal leakage in 3-state disabled mode, preventing unintended bus contention or signal corruption. |
| θJA | 58°C/W - Specifies thermal resistance for SOIC-DW package; allows calculation of junction temperature rise under typical 15–20 mA ICC conditions. |
| VIL / VIH | 0.8 V / 2.0 V - Defines TTL-compatible input thresholds, ensuring robust noise margins (>0.4 V) against ground bounce or crosstalk. |
| Propagation Delay Skew | ≤3 ns (max tPLH – min tPHL) - Guarantees tight channel-to-channel timing alignment critical for parallel bus integrity. |
Pinout & Package
SN74ALS540DWR uses a 20-pin SOIC (DW) package per JEDEC MS-013: 7.5 mm × 5.3 mm body, 1.27 mm lead pitch, 2.65 mm max height, gull-wing leads, RoHS-compliant NiPdAu finish, and MSL Level-1 handling.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2, 3, 4, 5, 6, 7, 8 | A1–A8 Inputs | Inverting data inputs; accept TTL-level signals and drive internal buffers with pnp input structure to minimize source loading. |
| 9 | GND | Ground reference for all internal circuitry and output stages; must be low-impedance connection to avoid noise coupling. |
| 10, 20 | VCC | Primary 5 V supply; dual VCC pins reduce IR drop and improve power distribution across the die. |
| 11, 19 | OE1, OE2 | Active-low 3-state enables (NOR logic); either high disables all outputs - supports flexible bus control via separate address/data enables. |
| 12, 13, 14, 15, 16, 17, 18, 19 | Y1–Y8 Outputs | Inverted buffered outputs; tri-state capable with <10 ns enable/disable transitions and <0.4 V VOL at 24 mA sink. |
| 20 | VCC | Second VCC connection - improves power delivery stability and reduces switching noise on shared bus lines. |
Key Features
| Feature | Design Value |
|---|---|
| Data flowthrough pinout | Inputs (A1–A8) on left side, outputs (Y1–Y8) on right side - eliminates layer crossings and vias in dense 8-bit bus routing. |
| Dual 3-state enable logic | OE1 and OE2 form a 2-input NOR gate - allows independent control of buffer groups or redundancy for fault-tolerant designs. |
| pnp input structure | Reduces input current to ≤0.2 mA (IIL) - decreases loading on preceding drivers and improves fanout capability in cascaded logic. |
| TTL-compatible voltage thresholds | VIH = 2.0 V min, VIL = 0.8 V max - ensures interoperability with 74LS, 74F, and microcontroller GPIOs without level-shifting. |
| Low 3-state disable time | tPLZ = 2 ns to 12 ns - minimizes bus turnaround latency in bidirectional data transfer protocols. |
Applications
| Memory Address Buffering | Parallel Bus Isolation |
|---|---|
Use Scenario: Driving 16-bit address lines from a microprocessor to multiple memory chips (ROM/RAM) on a shared bus. IC Role / Device Role / Timing Role: Inverting octal buffer that isolates CPU address outputs from memory load capacitance while preserving signal polarity through inversion compensation in firmware. Use Value: Prevents address skew and timing violations by delivering matched 2–12 ns propagation delays across all eight channels and sustaining 24 mA drive into 50–100 pF net capacitance. |
Use Scenario: Enabling/disabling communication between two processor subsystems sharing a common data bus (e.g., main CPU and DMA controller). IC Role / Device Role / Timing Role: 3-state line driver controlled by OE1/OE2 to assert/relinquish bus ownership with sub-10 ns disable timing. Use Value: Eliminates bus contention risk during handoff cycles; high-impedance leakage <±20 µA prevents false reads during transition windows. |
| Legacy System Bus Expansion | TTL-Level Signal Conditioning |
Use Scenario: Adding peripheral I/O ports to industrial PLC backplanes using discontinued 74ALS240-based designs. IC Role / Device Role / Timing Role: Pin-compatible upgrade path for SN74ALS240A with improved layout-friendly pinout and identical electrical specs. Use Value: Maintains system timing margins while simplifying board rework - no trace rerouting needed due to mirrored A/Y placement. |
Use Scenario: Converting noisy or weak signals from sensors or front-panel switches into clean, rail-to-rail TTL levels for FPGA or MCU input capture. IC Role / Device Role / Timing Role: Input conditioning buffer with 0.8 V/2.0 V thresholds and 20 µA input leakage, providing noise immunity and consistent edge definition. Use Value: Rejects EMI-induced glitches below 0.4 V margin and drives long cables with 24 mA sink strength without waveform degradation. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal inverting 3-state buffer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS540N | Same logic function and specs, but in 20-pin PDIP (N) package with θJA = 69°C/W and through-hole mounting. | Suitable for prototyping, low-volume industrial controls, or legacy repair where SOIC reflow is unavailable. | Select SN74ALS540N when manual soldering, socketing, or thermal derating above 58°C/W is acceptable. |
| SN74ALS540NSR | Identical functionality and SOIC pinout, but in 20-pin SOP (NS) package with 0.65 mm lead pitch and θJA = 60°C/W. | Used in space-constrained consumer electronics where finer pitch enables higher board density than DW. | Choose SN74ALS540NSR only if PCB layout supports 0.65 mm pitch and thermal budget allows +2°C/W penalty vs. DW. |
Compared with SN74ALS540N and SN74ALS540NSR, the SN74ALS540DWR offers the lowest thermal resistance (58°C/W) among SOIC/SOP variants and is optimized for automated SMT production with MSL Level-1 handling - making it the preferred choice for volume-manufactured industrial and computing equipment requiring long-term reliability and thermal headroom.
Availability
SN74ALS540DWR is available at Aetrix Electronics and suitable for memory address buffering, parallel bus isolation, and legacy TTL system expansion requiring stable component supply and full lifecycle support.
Supply support for SN74ALS540DWR 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 specializing in analog, embedded processing, and logic technologies with over 50 years of innovation in industrial, automotive, and communications markets.
The SN74ALS540DWR belongs to TI's legacy 74ALS logic family, engineered for high-speed, low-power TTL-compatible interfacing in mission-critical industrial control and computing infrastructure where reliability and pin-level consistency are essential.
FAQ
What logic function does SN74ALS540DWR implement?
The SN74ALS540DWR implements an octal inverting buffer with 3-state outputs: each input A1–A8 is inverted and appears at corresponding Y1–Y8 when enabled. Dual OE1/OE2 inputs use NOR logic - asserting either high places all outputs in high-impedance state. This function is confirmed in the logic diagram and truth table of the SDAS025D datasheet.
Does SN74ALS540DWR support 3.3 V operation?
No, SN74ALS540DWR is specified only for 4.5 V to 5.5 V supply operation per recommended conditions in SDAS025D. It lacks 3.3 V input thresholds or output drive capability; applying 3.3 V VCC risks undefined logic states and violates absolute maximum ratings. Use SN74LVC541A or similar for 3.3 V systems.
What is the thermal performance of SN74ALS540DWR in its SOIC-DW package?
The SN74ALS540DWR has a junction-to-ambient thermal resistance (θJA) of 58°C/W in the SOIC-DW package, as documented in the Absolute Maximum Ratings table of SDAS025D. This value assumes standard JEDEC 2-layer board conditions and enables accurate junction temperature estimation under typical 15–20 mA ICC operating current.
How does the pinout of SN74ALS540DWR simplify PCB layout?
The SN74ALS540DWR uses a data flowthrough pinout: inputs A1–A8 occupy pins 1–8 on the left side, outputs Y1–Y8 occupy pins 12–19 on the right side, with GND (pin 9) and dual VCC (pins 10, 20) centrally located. This arrangement allows straight-through trace routing for 8-bit buses without layer changes or vias - directly reducing signal skew and layout complexity.
Is SN74ALS540DWR pin-compatible with SN74ALS240A?
Yes, SN74ALS540DWR is functionally and pin-compatible with SN74ALS240A per the datasheet description stating it "offers a pinout with inputs and outputs on opposite sides" to match the SN74ALS240A layout. Both share identical 20-pin SOIC-DW pin assignments, logic function, and electrical specs - enabling drop-in replacement in legacy designs.
SN74ALS540DWR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- 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:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
SN74ALS540DWR FAQ
1.How can I place an order for SN74ALS540DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS540DWR 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 SN74ALS540DWR reliable?
The price and inventory of SN74ALS540DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS540DWR is usually 5 days.
3.What payment methods are accepted for SN74ALS540DWR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS540DWR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS540DWR?
SN74ALS540DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS540DWR 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 SN74ALS540DWR?
For technical support, including SN74ALS540DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS540DWR requirements.
6.How does Aetrix verify that SN74ALS540DWR is sourced from the original manufacturer or authorized distributors?
All SN74ALS540DWR 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 SN74ALS540DWR meets industry standards.
7.What is the process for return or replacement of SN74ALS540DWR?
All SN74ALS540DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS540DWR, 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 SN74ALS540DWR part is unused and in its original packaging.
Return procedure for SN74ALS540DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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