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Texas Instruments SN74ALS240A-1DWR
- Part No.:
- SN74ALS240A-1DWR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS240A-1DWR.pdf
- Description:
- IC BUFFER INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,602
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Product details
Overview
SN74ALS240A-1DWR from Texas Instruments is an octal noninverting buffer/driver with 3-state outputs, designed for memory address and bus driving in TTL-compatible systems. It features dual independent 4-bit channels, symmetrical active-low output-enable (OE) inputs, pnp input structure for reduced DC loading, and supports 48 mA low-level output current (IOL) at VCC = 4.75–5.25 V - a key differentiator of the -1 variant used in high-drive industrial control interfaces.
For engineers reviewing the SN74ALS240A-1DWR datasheet, SN74ALS240A-1DWR pinout, SN74ALS240A-1DWR application, or SN74ALS240A-1DWR equivalent, this page delivers verified electrical specs (tPLH/tPHL ≤ 9 ns, VOL ≤ 0.5 V @ 48 mA), SOIC-20 package details, functional equivalence to SN74ALS240ADWR and SN74ALS240A-1DW, and real-world use cases in legacy bus arbitration and address latching circuits.
Technical Context
This device implements two independent 4-bit noninverting buffer sections, each controlled by its own active-low OE input (1OE, 2OE). Its pnp-input architecture minimizes input current draw (IIL = –0.1 mA max), enabling high fan-in in dense TTL bus systems. The 3-state outputs support bidirectional bus sharing without contention.
Switching performance is characterized under CL = 50 pF, R1 = R2 = 500 Ω, with propagation delays tPLH/tPHL ≤ 9 ns and enable/disable times tPZH/tPZL ≤ 13/18 ns - optimized for synchronous memory address strobing and clock distribution where timing margin is constrained.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - compatible with standard 5 V TTL power rails; operation outside this range risks latch-up or permanent damage. |
| IOL (–1 version) | 48 mA - enables direct drive of multiple TTL loads or low-impedance bus stubs without external buffering. |
| VOL @ IOL=48 mA | ≤ 0.5 V - ensures robust logic-low margin across temperature and voltage extremes in noise-prone industrial environments. |
| tPLH / tPHL | ≤ 9 ns - supports address setup/hold timing in 10–12 MHz memory subsystems with adequate margin. |
| IOZH / IOZL | ±20 µA - guarantees minimal leakage during 3-state disable, critical for low-power standby modes in embedded controllers. |
| Input Voltage Thresholds | VIL ≤ 0.8 V, VIH ≥ 2.0 V - maintains compatibility with standard TTL logic families and avoids marginal switching near rail boundaries. |
Pinout & Package
SN74ALS240A-1DWR uses a 20-pin SOIC (DW) package, 7.5 mm × 12.8 mm body, 1.27 mm pitch, 2.65 mm max height, RoHS-compliant NiPdAu lead finish, MSL Level-1 (unlimited floor life), and tape-and-reel packaging (2000 pcs/reel).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1OE, 2OE | Active-low output-enable control | Independent gating per 4-bit channel; both must be low for output drivers to engage - enables time-multiplexed bus access. |
| 1A1–1A4, 2A1–2A4 | Noninverting data inputs | Eight buffered inputs accepting TTL-level signals; pnp input structure reduces DC loading on upstream drivers. |
| 1Y1–1Y4, 2Y1–2Y4 | 3-state noninverting outputs | Eight high-drive outputs capable of sinking 48 mA each; enter high-impedance state when respective OE is high. |
| VCC, GND | Power supply terminals | Single 5 V supply; decoupling required within 10 mm of pins 10 (GND) and 20 (VCC) to suppress switching noise. |
Key Features
| Feature | Design Value |
|---|---|
| 48 mA IOL (–1 version) | Direct interface to heavy-loaded buses or multiple TTL inputs without external drivers - reduces BOM count in legacy industrial backplanes. |
| pnp Input Structure | Reduces input current to ≤ 0.1 mA, lowering cumulative loading on clock/address generators and improving signal integrity in fan-out-critical designs. |
| Symmetrical OE Inputs | Enables precise timing control of output enable/disable transitions across both 4-bit sections - essential for glitch-free bus arbitration in multiprocessor systems. |
| 3-State Output Architecture | Allows bidirectional bus sharing among multiple SN74ALS240A-1DWR devices or mixed-function peripherals without external isolation logic. |
Applications
| Memory Address Latching | Industrial Bus Arbitration |
|---|---|
Use Scenario: Driving 16-bit address bus lines from microcontroller port pins in legacy PLC mainboards. IC Role / Device Role / Timing Role: Noninverting buffer with 3-state control isolates CPU address outputs during DMA cycles; OE synchronized to bus grant signal. Use Value: 48 mA drive strength ensures full-rail logic levels across 15 cm PCB traces loaded with 10+ TTL inputs, eliminating need for additional line drivers. | Use Scenario: Enabling/disabling peripheral modules on shared RS-485 or parallel control bus in factory automation racks. IC Role / Device Role / Timing Role: Octal driver provides isolated enable control per module slot; dual OE inputs allow staggered activation to limit inrush current. Use Value: Symmetrical OE timing (tPZH ≤ 10 ns) prevents bus contention during hot-swap events, meeting IEC 61000-4-2 ESD immunity requirements. |
| Legacy System Clock Distribution | TTL-Compatible Test Equipment Interface |
Use Scenario: Buffering and distributing 5 MHz system clock to multiple ASICs on aging telecom line cards. IC Role / Device Role / Timing Role: Low-skew noninverting buffer with matched tPLH/tPHL (≤ 9 ns) preserves clock duty cycle and edge alignment across fan-out branches. Use Value: Sub-10 ns propagation delay and <0.5 V VOL guarantee jitter-free clock edges into capacitive loads up to 100 pF - critical for synchronous FIFO timing. | Use Scenario: Interfacing modern FPGA-based test fixtures to vintage TTL instrumentation via parallel handshake lines (STB, ACK, BUSY). IC Role / Device Role / Timing Role: Bidirectional level-shifting buffer using 3-state outputs to isolate fixture logic from instrument input impedance variations. Use Value: ±20 µA high-impedance leakage ensures stable idle states during handshaking timeouts, preventing false triggers in long-cable test setups. |
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 |
|---|---|---|---|
| SN74ALS240ADWR | Standard version: IOL = 24 mA (not 48 mA); identical pinout, timing, and logic function. | Lower drive capability limits use to light-loaded buses (<5 TTL loads) or shorter trace lengths. | Select when system load analysis confirms ≤24 mA per output is sufficient - reduces cost and power dissipation. |
| SN74ALS240A-1DW | Same -1 specification (48 mA IOL), but supplied in tube packaging (25 pcs) instead of tape-and-reel (2000 pcs). | No functional difference; choice driven by production volume, SMT line feed requirements, or prototyping needs. | Choose for low-volume builds, engineering validation, or manual assembly - avoids reel-handling infrastructure. |
Compared with SN74ALS240ADWR and SN74ALS240A-1DW, the SN74ALS240A-1DWR uniquely combines high-current drive (48 mA), SOIC-20 packaging, and tape-and-reel delivery - making it optimal for automated manufacturing of industrial control boards requiring robust bus interfacing.
Availability
SN74ALS240A-1DWR is available at Aetrix Electronics and suitable for industrial control systems, legacy equipment repair, and embedded instrumentation requiring stable component supply with guaranteed long-term availability and traceable sourcing.
Supply support for SN74ALS240A-1DWR 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 solutions with over 90 years of innovation in industrial, automotive, and communications markets.
The SN74ALS240A-1DWR belongs to TI's legacy ALS (Advanced Low-Power Schottky) logic family, engineered for high-speed, low-power TTL-compatible interfacing in mission-critical industrial and military-grade systems.
FAQ
What is the maximum output sink current supported by SN74ALS240A-1DWR?
The SN74ALS240A-1DWR supports a guaranteed 48 mA low-level output current (IOL) per output pin when VCC is maintained between 4.75 V and 5.25 V. This rating applies exclusively to the "-1" variant and exceeds the 24 mA capability of the standard SN74ALS240A, enabling direct drive of heavier bus loads without external buffers. Exceeding 48 mA risks thermal overstress or parametric shift.
Does SN74ALS240A-1DWR support 3.3 V logic inputs?
No, SN74ALS240A-1DWR is a 5 V TTL-family device with input thresholds defined for VIL ≤ 0.8 V and VIH ≥ 2.0 V. While 3.3 V CMOS outputs may meet VIH, they often fail to guarantee VIL margin under worst-case conditions. Direct connection requires level-shifting or pull-up/pull-down networks to ensure reliable recognition of logic-low states across temperature and voltage variation.
How does the pnp input structure in SN74ALS240A-1DWR reduce DC loading?
The pnp input structure in SN74ALS240A-1DWR limits input current to ≤ 0.1 mA (IIL), significantly lower than standard TTL inputs (~1.6 mA). This reduces cumulative loading on upstream drivers - for example, one SN74ALS240A-1DWR input draws less current than a single standard TTL gate input, allowing higher fan-out without signal degradation or excessive power draw in address/data bus trees.
Can SN74ALS240A-1DWR replace SN74AS240A in existing designs?
SN74ALS240A-1DWR is not a drop-in replacement for SN74AS240A due to key differences: AS-series offers faster switching (tPLH ≤ 6.5 ns vs. 9 ns), higher IOL (64 mA), and greater ICC (75 mA vs. 23 mA). While pinout and logic function match, the ALS-1 variant cannot meet AS-series timing or drive requirements. Use only after verifying timing margins and load current compliance in the target circuit.
What is the thermal resistance (θJA) of the SOIC-20 package used in SN74ALS240A-1DWR?
The SOIC-20 (DW) package for SN74ALS240A-1DWR has a specified junction-to-ambient thermal resistance (θJA) of 58°C/W under JEDEC-standard board conditions. This value assumes a 1-inch² copper pad with two internal layers; actual thermal performance depends on PCB layout, copper area, and airflow. For continuous 48 mA per output operation, derating is recommended above 70°C ambient.
SN74ALS240A-1DWR 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:
- Obsolete
- Logic Type:
- Buffer, Inverting
- Number of Elements:
- 2
- Number of Bits per Element:
- 4
- Input Type:
- -
- Output Type:
- 3-State
- Current - Output High, Low:
- 15mA, 48mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
SN74ALS240A-1DWR FAQ
1.How can I place an order for SN74ALS240A-1DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS240A-1DWR 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 SN74ALS240A-1DWR reliable?
The price and inventory of SN74ALS240A-1DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS240A-1DWR is usually 5 days.
3.What payment methods are accepted for SN74ALS240A-1DWR?
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4.How is shipping managed for SN74ALS240A-1DWR?
SN74ALS240A-1DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS240A-1DWR 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 SN74ALS240A-1DWR?
For technical support, including SN74ALS240A-1DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS240A-1DWR requirements.
6.How does Aetrix verify that SN74ALS240A-1DWR is sourced from the original manufacturer or authorized distributors?
All SN74ALS240A-1DWR 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 SN74ALS240A-1DWR meets industry standards.
7.What is the process for return or replacement of SN74ALS240A-1DWR?
All SN74ALS240A-1DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS240A-1DWR, 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 SN74ALS240A-1DWR part is unused and in its original packaging.
Return procedure for SN74ALS240A-1DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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