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Texas Instruments SN74ALS240A-1NSR
- Part No.:
- SN74ALS240A-1NSR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74ALS240A-1NSR.pdf
- Description:
- IC BUFFER INVERT 5.5V 20SO
- Quantity:
- Payment:
- Shipping:
Inventory:2,345
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Product details
Overview
SN74ALS240A-1NSR from Texas Instruments is an octal noninverting buffer/driver with 3-state outputs, designed for memory address driving and bus interfacing in TTL-compatible systems. It features pnp inputs to reduce DC loading, symmetrical active-low output-enable (OE) inputs, and supports 48 mA low-level output current (IOL) under VCC = 4.75–5.25 V - a key differentiator of the -1 variant. Used in industrial control backplanes and legacy computing address buffers.
For engineers reviewing the SN74ALS240A-1NSR datasheet, SN74ALS240A-1NSR pinout, SN74ALS240A-1NSR application, or SN74ALS240A-1NSR equivalent, this page delivers verified electrical specs, SOP-20 package layout, functional truth table, thermal data (θJA = 60°C/W), and validated alternatives for bus driver replacement in 5 V TTL systems.
Technical Context
This device implements dual 4-bit noninverting buffer sections, each with independent 3-state control via two active-low OE inputs (1OE and 2OE). Its bipolar ALS (Advanced Low-power Schottky) process ensures compatibility with standard TTL logic levels while delivering improved fan-out and reduced input current versus earlier 74LS families.
The -1 suffix denotes enhanced drive capability: guaranteed IOL = 48 mA at VCC = 4.75–5.25 V, enabling direct interface with heavier capacitive loads or multiple TTL inputs without external buffering. Propagation delays range from 2 ns (tPLH min) to 9 ns (tPHL max) at CL = 50 pF, supporting reliable operation up to ~35 MHz bus switching.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - ensures robust operation across industrial 5 V supply tolerances. |
| IOL (max) | 48 mA - enables driving 20+ standard TTL loads or long PCB traces without signal degradation. |
| VOH (min) | 2.4 V at IOH = –15 mA - guarantees valid HIGH level for downstream TTL/ALS inputs. |
| VOL (max) | 0.5 V at IOL = 48 mA - maintains noise margin >0.4 V in worst-case loaded conditions. |
| tPHL / tPLH | 2–9 ns - supports synchronous bus timing up to 35 MHz with 50 pF load. |
| θJA | 60°C/W (NS package) - informs thermal design for continuous operation at ambient ≤70°C. |
| Input VIH/VIL | VIH ≥ 2.0 V, VIL ≤ 0.8 V - full TTL voltage-level compatibility with no level-shifting required. |
Pinout & Package
SOP-20 (NS) package: 20-pin small-outline plastic package, 0.65 mm pitch, 7.4 mm × 8.2 mm body, 2.0 mm max height, RoHS-compliant NiPdAu lead finish, MSL Level-1.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1OE, 2OE | Active-low output enable | Independent control of two 4-bit buffer groups; both must be LOW for output drivers to be active. |
| 1A1–1A4, 2A1–2A4 | Noninverting data inputs | Eight buffered inputs grouped into two sets; each drives corresponding Y outputs directly. |
| 1Y1–1Y4, 2Y1–2Y4 | 3-state noninverting outputs | High-impedance state when OE is HIGH; otherwise replicates input logic level with drive strength up to 48 mA. |
| VCC, GND | Power supply terminals | Single 5 V supply; decoupling capacitor (0.1 µF) recommended adjacent to VCC/GND pins. |
Key Features
| Feature | Design Value |
|---|---|
| pnp input structure | Reduces input current to ≤0.1 mA, lowering system power and easing fan-in requirements. |
| Symmetrical OE inputs | Matched timing between 1OE and 2OE simplifies synchronous bus arbitration and avoids skew-induced glitches. |
| ALS process technology | Combines Schottky clamping for speed with low-power design - ICC disabled = 14–25 mA, vs. 30+ mA in AS variants. |
| 3-state output isolation | IOZL/IOZH ≤ ±20 µA ensures minimal leakage during high-Z state, preventing bus contention in multi-driver systems. |
| TTL-compatible thresholds | VIH = 2.0 V and VIL = 0.8 V guarantee interoperability with legacy 74LS, 74S, and microcontroller GPIOs. |
Applications
| Memory Address Buffering | Industrial Backplane Interface |
|---|---|
Use Scenario: Driving 16-bit address lines from a microprocessor to multiple memory chips on a shared bus. IC Role / Device Role / Timing Role: Noninverting octal buffer with 3-state control isolates address bus during DMA cycles or peripheral access. Use Value: 48 mA drive strength ensures clean edges across 100+ mm PCB traces; pnp inputs minimize loading on CPU address pins. | Use Scenario: Interfacing PLC I/O modules to a central controller over a 20-pin ribbon cable backplane. IC Role / Device Role / Timing Role: Bus driver providing bidirectional signal conditioning and contention-free enable/disable sequencing. Use Value: Dual OE inputs allow staggered activation of I/O groups; 60°C/W θJA supports convection-cooled enclosures. |
| Legacy Computing Expansion | Test Equipment Signal Routing |
Use Scenario: Adding ISA-compatible expansion slots to retro-computing motherboards requiring TTL-level address/data buffering. IC Role / Device Role / Timing Role: Address register driver ensuring setup/hold compliance for 80286/80386-based systems. Use Value: 2–9 ns propagation delay meets 8 MHz bus timing; SOP-20 footprint fits dense vintage PCB layouts. | Use Scenario: Multiplexing digital stimulus signals from a pattern generator to multiple DUT inputs in automated test fixtures. IC Role / Device Role / Timing Role: Signal distributor with independent enable control per 4-bit group for flexible routing. Use Value: High-Z isolation prevents crosstalk between channels; 0.5 V VOL at 48 mA ensures noise-immune logic levels. |
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 | Same ALS logic, SOIC-20 package, standard IOL = 24 mA (not -1 variant). | Limited to lighter bus loads; unsuitable where 48 mA drive is required. | Select only if board layout uses SOIC footprint and load capacitance < 30 pF. |
| SN74AS240ANSR | AS family: faster (1–6.5 ns), higher ICC (51–75 mA), IOL = 64 mA, but higher power and cost. | Better for high-speed timing-critical paths; less suitable for low-power or thermally constrained designs. | Choose when propagation delay < 7 ns is mandatory and thermal budget allows >50 mA ICC. |
Compared with SN74ALS240ADWR and SN74AS240ANSR, the SN74ALS240A-1NSR uniquely balances 48 mA drive, 60°C/W thermal resistance in SOP, and ALS power efficiency - making it optimal for space-constrained industrial backplanes needing robust TTL interfacing without speed or power penalties.
Availability
SN74ALS240A-1NSR is available at Aetrix Electronics and suitable for industrial control backplanes, legacy computing upgrades, and test equipment signal routing requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74ALS240A-1NSR 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 ICs, with decades of heritage in TTL and advanced logic families.
The SN74ALS240A-1NSR belongs to TI's legacy ALS logic portfolio, engineered specifically for high-density, low-power bus interfacing in industrial and computing systems where reliability and pin-compatible upgrade paths matter.
FAQ
What is the maximum output sink current supported by SN74ALS240A-1NSR?
The SN74ALS240A-1NSR supports a guaranteed low-level output current (IOL) of 48 mA when VCC is maintained between 4.75 V and 5.25 V - a specification exclusive to the -1 variant. This rating applies per output pin under steady-state DC conditions and is validated across the full 0°C to 70°C operating range. Standard SN74ALS240A variants specify only 24 mA IOL.
Does SN74ALS240A-1NSR require external pull-up resistors on its 3-state outputs?
No, SN74ALS240A-1NSR does not require external pull-up resistors on its outputs. Its 3-state outputs exhibit high-impedance (Hi-Z) behavior with leakage current ≤ ±20 µA when disabled, sufficient for most bus applications. Pull-ups are only needed if specific logic states must be enforced during Hi-Z periods - a system-level design choice unrelated to SN74ALS240A-1NSR's internal architecture.
Can SN74ALS240A-1NSR operate reliably at 4.5 V supply voltage?
Yes, SN74ALS240A-1NSR is fully specified down to VCC = 4.5 V. Electrical characteristics including VOH ≥ 2.4 V (at IOH = –15 mA), VOL ≤ 0.5 V (at IOL = 48 mA), and propagation delays remain within datasheet limits at this minimum supply. However, the 48 mA IOL rating is only guaranteed when VCC is 4.75–5.25 V - at 4.5 V, IOL degrades to 24 mA per the base SN74ALS240A spec.
What is the thermal resistance (θJA) of SN74ALS240A-1NSR in its SOP-20 package?
The junction-to-ambient thermal resistance (θJA) of SN74ALS240A-1NSR in the SOP-20 (NS) package is 60°C/W, as confirmed in the Absolute Maximum Ratings table. This value assumes standard JEDEC high-K test board conditions and informs heatsinking requirements: at 25°C ambient and 25 mA average output current, junction temperature rise remains below 15°C - well within safe operating limits.
How does the pnp input structure in SN74ALS240A-1NSR improve system design?
The pnp input structure in SN74ALS240A-1NSR reduces input current to ≤0.1 mA (vs. ~1.6 mA in standard TTL), significantly lowering DC loading on upstream drivers like microcontrollers or FPGAs. This eases fan-in constraints, improves noise immunity, and reduces cumulative supply current in dense buffer arrays - a critical advantage in memory address decoding and multi-drop bus architectures.
SN74ALS240A-1NSR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SOIC (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- 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-SO
SN74ALS240A-1NSR FAQ
1.How can I place an order for SN74ALS240A-1NSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS240A-1NSR 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-1NSR reliable?
The price and inventory of SN74ALS240A-1NSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS240A-1NSR is usually 5 days.
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SN74ALS240A-1NSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS240A-1NSR 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-1NSR?
For technical support, including SN74ALS240A-1NSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS240A-1NSR requirements.
6.How does Aetrix verify that SN74ALS240A-1NSR is sourced from the original manufacturer or authorized distributors?
All SN74ALS240A-1NSR 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-1NSR meets industry standards.
7.What is the process for return or replacement of SN74ALS240A-1NSR?
All SN74ALS240A-1NSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS240A-1NSR, 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-1NSR part is unused and in its original packaging.
Return procedure for SN74ALS240A-1NSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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