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Texas Instruments SN74ALS240A-1N
- Part No.:
- SN74ALS240A-1N
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74ALS240A-1N.pdf
- Description:
- IC BUFFER INVERT 5.5V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:494
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Product details
Overview
SN74ALS240A-1N 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 48 mA low-level output current (IOL), supports 0°C to 70°C ambient, and uses a 20-pin PDIP package for through-hole mounting in industrial control and legacy computing applications.
For engineers reviewing the SN74ALS240A-1N datasheet, SN74ALS240A-1N pinout, SN74ALS240A-1N application, or SN74ALS240A-1N equivalent, key selection criteria include guaranteed 48 mA sink capability under 4.75–5.25 V, 3-state enable timing (tPZL ≤ 18 ns), ALS logic family compatibility, and PDIP-20 mechanical fit for retrofits and repair.
Technical Context
This device implements dual 4-bit noninverting buffers with independent active-low 3-state enable inputs (1OE, 2OE). Each buffer pair shares one OE signal, allowing grouped bus control. The ALS process provides higher speed and lower power than standard TTL while maintaining pin-compatible replacement for 74LS240.
Input structure uses pnp-based circuitry to reduce dc loading on driving sources. Output stages are totem-pole with symmetrical drive strength optimized for bus termination and address register buffering - not open-collector or push-pull with asymmetric sourcing/sinking.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - Ensures compatibility with standard 5 V TTL/ALS supply rails and tolerates ±5% regulation drift. |
| IOL (max) | 48 mA - Guaranteed sink current per output when VCC = 4.75–5.25 V, enabling direct drive of multiple TTL loads or unterminated buses. |
| tPLH / tPHL | 2–9 ns - Propagation delay from input to enabled output ensures sub-10 ns timing for high-speed address latching in 1980s–1990s microprocessor systems. |
| tPZL / tPLZ | 5–18 ns - 3-state disable/enable timing allows clean bus release before new driver activation, preventing contention in shared-data-path designs. |
| VIL / VIH | 0.8 V / 2.0 V - Input threshold levels match standard TTL logic families, ensuring interoperability without level-shifting in mixed-logic systems. |
| ICC (disabled) | 14–25 mA - Quiescent supply current when outputs are disabled reflects ALS family efficiency versus earlier TTL, reducing system-level power overhead. |
Pinout & Package
SN74ALS240A-1N is housed in a 20-pin plastic dual in-line package (PDIP-N) with 0.300-inch body width and 0.100-inch lead pitch. Pin 1 is located at the top-left corner adjacent to the notch or dot marking.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1OE | Output Enable (Group 1) | Active-low control for Y1–Y4 outputs; ties to system bus controller or address decoder for selective group enable. |
| 2OE | Output Enable (Group 2) | Active-low control for Y5–Y8 outputs; enables independent gating of second buffer quad for split-bus architectures. |
| 1A1–1A4 | Inputs (Group 1) | Noninverting data inputs for first four buffers; routed from CPU address lines or peripheral registers. |
| 2A1–2A4 | Inputs (Group 2) | Noninverting data inputs for second four buffers; used for parallel data paths or mirrored address segments. |
| 1Y1–1Y4 | Outputs (Group 1) | 3-state buffered outputs driven by 1A1–1A4; connect directly to memory address bus or I/O data lines. |
| 2Y1–2Y4 | Outputs (Group 2) | 3-state buffered outputs driven by 2A1–2A4; support dual-bank memory or segmented bus expansion. |
| VCC | Power Supply | +5 V supply pin; requires local 0.1 µF ceramic decoupling adjacent to pin for noise suppression during switching. |
| GND | Ground Reference | Signal and power return; must be connected to low-impedance ground plane to maintain noise margin and timing integrity. |
Key Features
| Feature | Design Value |
|---|---|
| pnp input structure | Reduces DC input loading to ≤0.1 mA per input, minimizing fan-out burden on upstream TTL or CMOS drivers. |
| 48 mA IOL rating (-1 version) | Enables direct interface with legacy TTL loads (e.g., 74LSxx inputs) without external pull-ups or current amplification. |
| 3-state output symmetry | Matched enable/disable timing (tPZL/tPLZ ≤ 18 ns) prevents bus glitches during hot-swap or dynamic reconfiguration. |
| ALS logic family | Delivers 2× speed and 50% lower power vs. standard TTL, supporting higher-density board layouts in space-constrained systems. |
| Dual independent OE inputs | Allows partitioned bus control - e.g., upper/lower address byte enable - without external logic or multiplexing. |
Applications
| Memory Address Buffering | Clock Distribution |
|---|---|
Use Scenario: Driving 16-bit address bus in Z80- or 8086-based embedded controllers where address lines fan out to multiple RAM/ROM chips. IC Role / Device Role / Timing Role: Noninverting octal buffer providing isolation and current gain between CPU address pins and memory chip address inputs. Use Value: Eliminates need for discrete transistor arrays or multiple 74LS04 inverters, reducing component count and PCB area while guaranteeing 48 mA sink per line. | Use Scenario: Distributing a single system clock signal to multiple synchronous peripherals (e.g., UART, timer, DMA controller) in industrial PLC modules. IC Role / Device Role / Timing Role: Low-skew, 3-state-capable clock driver enabling dynamic clock gating per peripheral via OE control. Use Value: Prevents clock contention during sleep/wake transitions and maintains <9 ns propagation delay across all eight outputs for deterministic timing. |
| Bus Transceiver Interface | Legacy System Repair |
Use Scenario: Bidirectional data bus isolation between microcontroller and external EPROM or SRAM in ISA-style expansion cards. IC Role / Device Role / Timing Role: One-directional buffer stage (used with complementary SN74ALS241A) to enforce unidirectional flow and prevent bus contention. Use Value: Provides 3-state control synchronized to read/write strobes, eliminating bus turnaround delays and simplifying timing budgeting. | Use Scenario: Replacement for failed SN74LS240 in vintage test equipment, arcade boards, or military avionics maintenance spares. IC Role / Device Role / Timing Role: Pin- and function-compatible drop-in upgrade offering improved reliability and extended temperature range (0°C to 70°C). Use Value: Maintains identical pinout and logic behavior while delivering 2× higher output drive and lower ICC, extending service life in aging hardware. |
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 | Standard version with 24 mA max IOL (vs. 48 mA for -1N); otherwise identical pinout, timing, and voltage specs. | Suitable only where load current ≤24 mA per output; insufficient for heavy TTL fan-out or unterminated buses. | Select SN74ALS240AN only if legacy design validation confirms lower drive requirement and cost sensitivity outweighs performance margin. |
| SN74AS240AN | Faster propagation (1–6.5 ns vs. 2–9 ns) and higher IOL (64 mA), but increased ICC (51–75 mA vs. 13–23 mA) and tighter VCC tolerance (4.5–5.5 V same). | Better for high-speed timing-critical paths but unsuitable where power budget or thermal dissipation is constrained. | Choose SN74AS240AN only when sub-7 ns delay is mandatory and system can accommodate +200% quiescent current increase. |
Compared with SN74ALS240AN and SN74AS240AN, SN74ALS240A-1N uniquely balances 48 mA drive capability with ALS-class power efficiency and proven field reliability in long-lifecycle industrial systems - making it optimal for repair, retrofit, and cost-sensitive volume production where moderate speed suffices.
Availability
SN74ALS240A-1N is available at Aetrix Electronics and suitable for memory address buffering, bus interfacing, and legacy system repair requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS240A-1N 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial, automotive, and aerospace qualification.
SN74ALS240A-1N belongs to TI's legacy ALS (Advanced Low-power Schottky) logic family, engineered for high-speed, low-power TTL-compatible digital interfacing in 1980s–1990s computing and control systems.
FAQ
What is the maximum output sink current specification for SN74ALS240A-1N?
The SN74ALS240A-1N guarantees a minimum low-level output current (IOL) of 48 mA per output 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 rating of the standard SN74ALS240AN, enabling robust drive of multiple TTL inputs or unterminated transmission lines without external buffering.
Is SN74ALS240A-1N pin-compatible with SN74LS240?
Yes, SN74ALS240A-1N is pin-compatible and functionally equivalent to SN74LS240, sharing identical 20-pin PDIP layout, input/output mapping, and active-low 3-state enable logic. However, SN74ALS240A-1N offers superior electrical performance: 2× faster propagation delay, 2× higher output sink current, and ~50% lower quiescent power consumption, making it a direct performance upgrade.
Does SN74ALS240A-1N support operation at 3.3 V?
No, SN74ALS240A-1N is specified only for 4.5 V to 5.5 V supply operation and is not rated for 3.3 V logic systems. Its input thresholds (VIL = 0.8 V, VIH = 2.0 V) and output voltage levels (VOH ≥ 2.4 V, VOL ≤ 0.5 V) are designed for 5 V TTL/ALS compatibility. Use TI's 74LVC240 or similar 3.3 V–tolerant buffers for modern low-voltage designs.
What is the thermal resistance (θJA) of the SN74ALS240A-1N PDIP package?
The SN74ALS240A-1N in its PDIP (N) package has a junction-to-ambient thermal resistance (θJA) of 70°C/W, as specified in the official Texas Instruments datasheet. This value assumes standard JEDEC-defined PCB mounting conditions (single-layer copper, 1 in² pad) and informs thermal design margins when operating at full output load across the 0°C to 70°C ambient range.
Can SN74ALS240A-1N be used in place of SN74ALS240A-1DW?
Yes, SN74ALS240A-1N and SN74ALS240A-1DW share identical logic functionality, timing, and DC specifications - including the 48 mA IOL rating - but differ only in package: PDIP-20 (through-hole) vs. SOIC-20 (surface-mount). Mechanical redesign is required for substitution, but no schematic or firmware changes are needed, preserving signal integrity and timing behavior in validated designs.
SN74ALS240A-1N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- 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, 48mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74ALS240A-1N FAQ
1.How can I place an order for SN74ALS240A-1N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS240A-1N 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-1N reliable?
The price and inventory of SN74ALS240A-1N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS240A-1N is usually 5 days.
3.What payment methods are accepted for SN74ALS240A-1N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS240A-1N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS240A-1N?
SN74ALS240A-1N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS240A-1N 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-1N?
For technical support, including SN74ALS240A-1N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS240A-1N requirements.
6.How does Aetrix verify that SN74ALS240A-1N is sourced from the original manufacturer or authorized distributors?
All SN74ALS240A-1N 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-1N meets industry standards.
7.What is the process for return or replacement of SN74ALS240A-1N?
All SN74ALS240A-1N units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS240A-1N, 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-1N part is unused and in its original packaging.
Return procedure for SN74ALS240A-1N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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