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Texas Instruments SN74AS240AN
- Part No.:
- SN74AS240AN
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74AS240AN.pdf
- Description:
- IC BUFFER INVERT 5.5V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:2,115
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Product details
Overview
SN74AS240AN 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 operates at 4.5–5.5 V, delivers 64 mA low-level output current, features 6.5 ns typical propagation delay (A→Y), and uses a 20-pin PDIP package for through-hole mounting in industrial control and legacy computing applications.
For engineers reviewing the SN74AS240AN datasheet, SN74AS240AN pinout, SN74AS240AN application, or SN74AS240AN equivalent, key selection criteria include its AS-family speed grade, 3-state bus-driving capability, TTL input compatibility, and PDIP-20 thermal performance (θJA = 70°C/W) in high-density logic designs.
Technical Context
The SN74AS240AN implements dual 4-bit noninverting buffers with independent active-low 3-state enable inputs (1OE, 2OE), supporting symmetrical bus arbitration. Its pnp input structure reduces DC loading on upstream drivers, while the AS process ensures faster switching than ALS variants.
Each buffer exhibits tPLH/tPHL ≤ 6.5 ns at VCC = 5 V and CL = 50 pF, with tPZH/tPZL ≤ 6.4 ns for output enable timing - enabling reliable operation in high-speed address/data multiplexing and clock distribution circuits.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply voltage | 4.5–5.5 V - compatible with standard 5 V TTL power rails without regulation overhead |
| Low-level output current (IOL) | 64 mA - drives heavy capacitive loads or multiple TTL inputs without external buffering |
| Propagation delay (A→Y) | ≤6.5 ns - supports >100 MHz address strobe rates in memory subsystems |
| 3-state disable time (tPZL) | ≤9.0 ns - enables fast bus turnaround in bidirectional data transfer protocols |
| Input voltage thresholds | VIL = 0.8 V, VIH = 2.0 V - ensures noise margin compliance with TTL logic families |
| Quiescent current (ICC) | 24–38 mA (outputs disabled) - defines static power budget in standby bus-hold configurations |
| Package thermal resistance | θJA = 70°C/W (PDIP) - determines maximum continuous power dissipation at ambient temperatures |
Pinout & Package
SN74AS240AN uses a 20-pin plastic dual in-line package (PDIP-N) with 0.300-inch body width and standard through-hole footprint. Pin 1 is located at the top-left corner adjacent to the notch or dot marking.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1OE, 2OE | Active-low output enable | Independent control of two 4-bit buffer groups; low = enabled, high = high-impedance |
| 1A1–1A4, 2A1–2A4 | Noninverting input | Eight buffered inputs accepting TTL-level signals; pnp input stage minimizes source loading |
| 1Y1–1Y4, 2Y1–2Y4 | Noninverting 3-state output | Eight drive-capable outputs; sink up to 64 mA each while maintaining VOL ≤ 0.55 V |
| VCC (Pin 20) | Positive supply | 5 V nominal rail; must be decoupled locally to suppress switching noise coupling into logic paths |
| GND (Pin 10) | Ground reference | Common return for all I/O and supply currents; requires low-inductance connection to minimize ground bounce |
Key Features
| Feature | Design Value |
|---|---|
| AS-series speed grade | 6.5 ns max A→Y propagation delay - 2× faster than ALS equivalents for timing-critical address latching |
| Dual independent 3-state controls | Separate 1OE/2OE pins allow interleaved bus access between two memory banks or peripheral sets |
| pnp input structure | Reduces input current to ≤ –1 mA at VIL, lowering fan-out burden on preceding gate stages |
| High-current 3-state outputs | 64 mA IOL rating enables direct drive of 20+ TTL loads or termination-resistor networks |
| TTL-compatible voltage thresholds | VIH = 2.0 V / VIL = 0.8 V ensures interoperability with 74LS, 74F, and microprocessor address/data buses |
Applications
| Memory Address Buffering | Bus Transceiver Interface |
|---|---|
Use Scenario: Driving 16-bit address lines from a microprocessor to multiple memory ICs with shared address decoding. IC Role / Device Role / Timing Role: Noninverting buffer isolating CPU address outputs while providing current gain and 3-state isolation during DMA cycles. Use Value: Enables clean address transitions at >10 MHz with minimal skew across all 8 bits per group, preventing memory access collisions. | Use Scenario: Bidirectional data path control between an FPGA and legacy parallel EEPROM or SRAM. IC Role / Device Role / Timing Role: Direction-controlled bus driver using 1OE/2OE to separate read/write data lanes on a common 8-bit bus. Use Value: Eliminates need for discrete transceivers; 64 mA sink capability handles EEPROM write-current surges without voltage droop. |
| Clock Distribution Network | Industrial PLC I/O Expansion |
Use Scenario: Fan-out of a system clock signal to multiple synchronous peripherals requiring phase-aligned timing. IC Role / Device Role / Timing Role: Low-skew buffer replicating clock edges with matched tPLH/tPHL across all outputs. Use Value: Achieves <1 ns inter-output skew at 50 MHz, meeting setup/hold margins for high-speed latch-based peripherals. | Use Scenario: Interfacing microcontroller GPIOs to 24 V industrial sensors and actuators via level-shifting and current amplification. IC Role / Device Role / Timing Role: Logic-level translator and current booster for open-collector sensor inputs and relay-driver outputs. Use Value: Directly sinks 64 mA per channel to drive electromechanical relays, reducing BOM count versus discrete transistor solutions. |
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 |
|---|---|---|---|
| SN74ALS240AN | Slower speed (9 ns max tPHL), lower IOL (24 mA), same pinout and logic function | Lower power consumption (ICC ≈ 13–23 mA) but insufficient for high-fanout or fast-cycle memory systems | Select when board layout constraints require identical footprint but timing budgets allow ≥10 ns delays |
| SN74F240N | F-series process: 8.5 ns max tPHL, 32 mA IOL, higher ICC (51–75 mA when active) | Higher noise immunity (VIH = 2.0 V, VIL = 0.8 V same), but less drive strength than AS variant | Choose for mixed-F/AS systems where legacy F-family compatibility is required over peak drive capability |
Compared with SN74ALS240AN and SN74F240N, the SN74AS240AN delivers the highest output drive (64 mA) and fastest propagation (6.5 ns), making it optimal for dense memory subsystems where bus settling time and fan-out capacity are limiting factors - without requiring PCB redesign.
Availability
SN74AS240AN is available at Aetrix Electronics and suitable for industrial control systems, legacy computer upgrades, and embedded instrumentation requiring stable component supply with long-term obsolescence management.
Supply support for SN74AS240AN 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 devices with over 50 years of industrial-grade product development.
The SN74AS240AN belongs to TI's 74AS logic family, engineered for high-speed, high-drive TTL-compatible applications in memory addressing, bus interfacing, and clock distribution where performance exceeds ALS/F-series limitations.
FAQ
What is the maximum operating temperature range for the SN74AS240AN?
The SN74AS240AN is rated for commercial operation from 0°C to +70°C. This range is defined in the recommended operating conditions table of the official datasheet (SDAS214E), and applies specifically to the PDIP-packaged SN74AS240AN variant. Operation outside this range may result in parametric degradation or functional failure.
Does the SN74AS240AN support true bidirectional data flow?
No, the SN74AS240AN is a unidirectional noninverting buffer with fixed input-to-output direction (A→Y). It does not support automatic direction sensing or internal bus arbitration. Bidirectional operation requires external control of 1OE/2OE signals and complementary circuitry - the SN74AS240AN itself only provides 3-state-enabled unidirectional drive.
Can the SN74AS240AN be used as a level shifter between 3.3 V and 5 V logic domains?
No - the SN74AS240AN is a 5 V-only device with VCC = 4.5–5.5 V requirement and TTL input thresholds (VIL = 0.8 V, VIH = 2.0 V). It cannot reliably accept 3.3 V logic-high signals, nor safely interface with 3.3 V receivers due to overvoltage risk on outputs. Use dedicated level translators like TXB0108 instead of SN74AS240AN for mixed-voltage systems.
What is the purpose of the pnp input structure in the SN74AS240AN?
As documented in the datasheet description, the pnp input structure in the SN74AS240AN reduces DC input loading - limiting IIL to –1 mA maximum at VIL = 0.4 V. This lowers fan-in burden on upstream drivers, allowing one SN74AS240AN input to be driven by more preceding gates without violating output current limits, improving system-level logic density.
Is the SN74AS240AN pin-compatible with the SN74LS240N?
Yes - the SN74AS240AN shares identical pinout, terminal functions, and 20-pin PDIP package dimensions with SN74LS240N and SN74ALS240AN. However, differences in speed, drive strength, and input characteristics mean direct substitution requires validation of timing margins and load compatibility; the SN74AS240AN is not a drop-in replacement without design review.
SN74AS240AN Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AS
- Package/Case:
- 20-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- 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, 64mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74AS240AN FAQ
1.How can I place an order for SN74AS240AN through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS240AN 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 SN74AS240AN reliable?
The price and inventory of SN74AS240AN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS240AN is usually 5 days.
3.What payment methods are accepted for SN74AS240AN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AS240AN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AS240AN?
SN74AS240AN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS240AN 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 SN74AS240AN?
For technical support, including SN74AS240AN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS240AN requirements.
6.How does Aetrix verify that SN74AS240AN is sourced from the original manufacturer or authorized distributors?
All SN74AS240AN 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 SN74AS240AN meets industry standards.
7.What is the process for return or replacement of SN74AS240AN?
All SN74AS240AN units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS240AN, 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 SN74AS240AN part is unused and in its original packaging.
Return procedure for SN74AS240AN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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