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Texas Instruments SN74ALS540DW
- Part No.:
- SN74ALS540DW
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS540DW.pdf
- Description:
- IC BUFFER INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,916
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Product details
Overview
SN74ALS540DW 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, data flowthrough pinout (inputs and outputs on opposite sides), and operates at 4.5–5.5 V supply. Its key role is bidirectional bus isolation in industrial control and legacy computing backplanes.
For engineers reviewing the SN74ALS540DW datasheet, SN74ALS540DW pinout, SN74ALS540DW application, or SN74ALS540DW equivalent, this page delivers verified electrical specs (IOL = 24 mA, tPLH ≤ 12 ns), SOIC-20 package details, thermal impedance (θJA = 58°C/W), and validated alternatives for bus interface redesigns requiring ALS logic speed and drive strength.
Technical Context
The SN74ALS540DW implements a dual-NOR 3-state control gate: either OE1 or OE2 high forces all eight Y outputs into high-impedance state. Its inverted output logic (A→Y̅) enables active-low bus driving and address inversion without external gates. The pnp input stage lowers input current draw versus standard TTL, reducing loading on preceding drivers.
It belongs to the ALS (Advanced Low-Power Schottky) family, delivering 2× speed and 50% lower power than original LS logic, with guaranteed operation across 0°C to 70°C. All timing parameters-including tPZH (5–15 ns) and tPLZ (2–12 ns)-are specified under 50 pF capacitive load and 500 Ω source termination per JEDEC test conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | ALS (Advanced Low-Power Schottky) - ensures compatibility with 74LS/74AS while improving speed-power tradeoff |
| Supply Voltage | 4.5 V to 5.5 V - supports standard +5 V rail with ±10% tolerance for robust industrial operation |
| Output Drive (IOL) | 24 mA (min) - sufficient to drive 10 LS-TTL loads or 20 ALS loads directly on shared bus lines |
| Propagation Delay | tPLH ≤ 12 ns, tPHL ≤ 9 ns - enables reliable operation up to ~40 MHz bus clocking in synchronous designs |
| 3-State Enable Time | tPZH ≤ 15 ns, tPLZ ≤ 12 ns - ensures fast bus release for time-critical arbitration and multiplexing |
| Input Structure | pnp-based - reduces input current to ≤ –0.2 mA (IIL), minimizing loading on upstream drivers and fanout constraints |
| Thermal Impedance | θJA = 58°C/W (SOIC-DW) - defines maximum power dissipation limit (~180 mW at 70°C ambient) for PCB layout thermal planning |
Pinout & Package
SN74ALS540DW uses a 20-pin SOIC (DW) package measuring 13.0 mm × 7.6 mm × 2.65 mm max height, with 1.27 mm lead pitch and gull-wing leads. Pin 1 is located at the top-left corner with index area marking, and the package complies with JEDEC MS-013.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2 | OE1, OE2 | Active-low 3-state enable inputs - NOR logic: either high disables all outputs; both low enables inverted output drive |
| 3–10 | A1–A8 | True logic inputs - drive internal inverters; pnp input structure minimizes DC loading on source |
| 11 | GND | Ground reference - must be low-impedance connection to minimize noise coupling into 3-state transitions |
| 12 | VCC | +5 V supply - requires local 0.1 µF ceramic decoupling adjacent to pin for stable switching performance |
| 13–20 | Y1–Y8 | Inverted 3-state outputs - Yn = A̅n when OE1=OE2=low; high-Z otherwise - suitable for bidirectional bus contention management |
Key Features
| Feature | Design Value |
|---|---|
| Data Flowthrough Pinout | Inputs (A1–A8) on left side, outputs (Y1–Y8) on right side - simplifies PCB routing by eliminating layer jumps in dense bus layouts |
| Dual 3-State Control | Independent OE1/OE2 inputs with NOR logic - enables flexible bus arbitration schemes using separate enable signals per subsystem |
| ALS Performance Tier | 24 mA sink capability and sub-15 ns propagation delays - bridges gap between LS speed and AS drive strength without AS-level power penalty |
| pnp Input Stage | IIL ≤ –0.2 mA - reduces fanout burden on preceding drivers, allowing one SN74ALS540DW input to load ≥20 ALS gates |
| Bus-Compatible Output Structure | True totem-pole outputs with defined VOH/VOL - ensures clean logic levels into 50 pF loads and interoperability with LS/ALS/AS families |
Applications
| Industrial PLC Backplane Interface | Legacy Computer Memory Address Buffering |
|---|---|
Use Scenario: Isolating CPU address bus from multiple peripheral modules in modular control cabinets with hot-swap capability. IC Role / Device Role / Timing Role: Inverting 3-state buffer managing unidirectional address propagation while enabling module-specific bus release during configuration cycles. Use Value: Dual OE inputs allow independent gating per slot; 24 mA drive sustains signal integrity across 30 cm ribbon cable runs at 8 MHz. |
Use Scenario: Driving 20-bit memory address registers in 1980s-era minicomputer expansion cards where space and power are constrained. IC Role / Device Role / Timing Role: Octal inverter buffer translating CPU address bits to memory IC inputs while providing bus contention protection during DMA cycles. Use Value: pnp inputs reduce loading on aging TTL address latches; 12 ns tPLH meets 8 MHz memory access timing budgets. |
| Test Equipment Digital I/O Expansion | Automated Test Fixture Signal Conditioning |
Use Scenario: Adding programmable digital stimulus/response channels to benchtop ATE controllers using FPGA I/O expansion headers. IC Role / Device Role / Timing Role: Level-shifting and bus-driving interface between 3.3 V FPGA I/O and 5 V DUT logic, with OE-controlled directionality. Use Value: 5.5 V absolute max rating allows safe operation with margin against FPGA I/O overshoot; SOIC-20 footprint fits compact carrier boards. |
Use Scenario: Conditioning and isolating control signals between microcontroller-based sequencers and high-current relay drivers in production test fixtures. IC Role / Device Role / Timing Role: Inverting buffer providing noise-immune signal translation and current gain for optocoupler inputs driving 12 V relays. Use Value: VOL ≤ 0.4 V at 24 mA ensures reliable turn-on of PC817 optocouplers; 58°C/W θJA supports convection-cooled fixture enclosures. |
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 ALS logic, identical electrical specs, but in 20-pin PDIP (N) package - θJA = 69°C/W, larger footprint, through-hole mount | Preferred for prototyping, manual assembly, or legacy through-hole PCBs; unsuitable for automated SMT lines | Select SN74ALS540N only if board design mandates through-hole mounting or requires higher thermal mass for intermittent high-current bursts |
| SN74ALS541DWR | Non-inverting octal 3-state buffer in same SOIC-20 (DW) package - identical timing, drive, and thermal specs, but Yn = An | Used where bus polarity must match source without external inversion; not functionally interchangeable without logic redesign | Choose SN74ALS541DWR when system architecture requires true (non-inverted) data path - verify signal polarity alignment before substitution |
Compared with SN74ALS540N, SN74ALS540DW offers superior thermal performance (58 vs. 69°C/W) and SMT manufacturability; compared with SN74ALS541DWR, it provides inverted logic essential for address decoding and active-low bus enable schemes without added gates.
Availability
SN74ALS540DW is available at Aetrix Electronics and suitable for industrial PLC backplane interfaces, legacy computer memory subsystems, and automated test equipment requiring stable component supply across extended product lifecycles.
Supply support for SN74ALS540DW 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 broad industrial, automotive, and communications reach.
The SN74ALS540DW belongs to TI's legacy 74ALS logic family, engineered for high-speed, low-power bus interfacing in industrial control, instrumentation, and retrocomputing systems where reliability and long-term availability are critical.
FAQ
What is the logic function of SN74ALS540DW?
The SN74ALS540DW is an octal inverting buffer with 3-state outputs: each output Yn equals the logical inverse of its corresponding input An (Yn = A̅n) when both OE1 and OE2 are low. When either OE1 or OE2 is high, all outputs enter high-impedance state. This function is confirmed in the device description and logic diagram of the SDAS025D datasheet.
Does SN74ALS540DW support 3.3 V operation?
No, SN74ALS540DW is specified only for 4.5 V to 5.5 V supply operation per recommended operating conditions. Its input thresholds (VIH = 2 V min, VIL = 0.8 V max) and output voltage levels (VOH ≥ 2.4 V at IOL = 12 mA) are designed for 5 V TTL/ALS compatibility. Operation below 4.5 V is not characterized and may result in undefined logic states or timing violations.
What is the maximum capacitive load SN74ALS540DW can drive reliably?
SN74ALS540DW switching characteristics (tPLH, tPHL, tPZH, etc.) are guaranteed with CL = 50 pF, as defined in the "Switching Characteristics" table of SDAS025D. While it may drive higher capacitance, timing margins degrade beyond 50 pF; for >50 pF loads, derating analysis or simulation with actual trace capacitance is required to ensure setup/hold compliance.
Is SN74ALS540DW pin-compatible with SN74ALS541DWR?
Yes, SN74ALS540DW and SN74ALS541DWR share identical SOIC-20 (DW) package dimensions, pin count, and pinout - including OE1, OE2, A1–A8, GND, VCC, and Y1–Y8 assignments. However, they differ functionally: SN74ALS540DW provides inverted outputs (Y = A̅), while SN74ALS541DWR provides true outputs (Y = A). Substitution requires logic-level verification.
What does the "-1" suffix mean in SN74ALS540-1DW?
The "-1" suffix denotes an enhanced-output version: SN74ALS540-1DW supports IOL = 48 mA (vs. 24 mA for standard SN74ALS540DW) when VCC is 4.75–5.25 V. This variant is not offered in DW packaging per TI's ordering information - only in N and NS packages. Therefore, SN74ALS540DW has no -1 variant; its rated IOL remains 24 mA.
SN74ALS540DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Bulk
- 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:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
SN74ALS540DW FAQ
1.How can I place an order for SN74ALS540DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS540DW 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 SN74ALS540DW reliable?
The price and inventory of SN74ALS540DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS540DW is usually 5 days.
3.What payment methods are accepted for SN74ALS540DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS540DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS540DW?
SN74ALS540DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS540DW 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 SN74ALS540DW?
For technical support, including SN74ALS540DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS540DW requirements.
6.How does Aetrix verify that SN74ALS540DW is sourced from the original manufacturer or authorized distributors?
All SN74ALS540DW 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 SN74ALS540DW meets industry standards.
7.What is the process for return or replacement of SN74ALS540DW?
All SN74ALS540DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS540DW, 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 SN74ALS540DW part is unused and in its original packaging.
Return procedure for SN74ALS540DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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