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Texas Instruments SN74ALS240A-1DBR
- Part No.:
- SN74ALS240A-1DBR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SSOP (0.209", 5.30mm Width)
- Datasheet:
-
SN74ALS240A-1DBR.pdf
- Description:
- IC BUFFER INVERT 5.5V 20SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:2,664
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Product details
Overview
SN74ALS240A-1DBR from Texas Instruments is an octal buffer/driver with 3-state outputs in a 20-pin SSOP (DB) package, designed for memory address driving and bus interfacing. It features pnp inputs to reduce DC loading, symmetrical active-low output-enable (OE) inputs, and supports 48 mA low-level output current (IOL) at VCC = 4.75–5.25 V - enabling robust bus termination in industrial control backplanes.
For engineers reviewing the SN74ALS240A-1DBR datasheet, SN74ALS240A-1DBR pinout, SN74ALS240A-1DBR application, or SN74ALS240A-1DBR equivalent, key selection criteria include its -1 version's enhanced sink capability, SSOP thermal performance (θJA = 70°C/W), compatibility with ALS/AS logic families, and use in 5-V TTL-compatible memory subsystems requiring high fan-out and fast enable/disable timing.
Technical Context
This device implements dual 4-bit noninverting buffers with independent 3-state control per group (1OE controls Y1–Y4; 2OE controls Y1–Y4 of second section). Each buffer operates with TTL-compatible input thresholds (VIL = 0.8 V, VIH = 2 V) and delivers rail-to-rail output swing under load.
Its architecture supports bidirectional bus isolation via OE-controlled high-impedance states, with propagation delays as low as 2 ns (tPLH/tPHL) and enable/disable times down to 1 ns (tPHZ/tPLZ) under CL = 50 pF conditions - optimized for synchronous address/data multiplexing in legacy microprocessor systems.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - ensures stable operation across standard 5-V TTL supply rails with ±10% tolerance. |
| IOL (–1 version) | 48 mA - enables direct drive of multiple TTL loads or termination resistors without external buffers. |
| tPLH / tPHL | 2 ns to 9 ns - supports high-speed address latching in 20–33 MHz CPU buses. |
| θJA (SSOP-DB) | 70°C/W - defines thermal derating limit for continuous operation at ambient up to 70°C in enclosed enclosures. |
| IOZH / IOZL | ±20 µA - specifies leakage during 3-state disable, critical for low-power standby modes in battery-backed systems. |
| VIL / VIH | 0.8 V / 2.0 V - matches standard TTL input thresholds, ensuring interoperability with 74LS/74ALS logic families. |
| ICC (Outputs disabled) | 14–25 mA - quantifies quiescent power draw when all outputs are tri-stated, relevant for system-level power budgeting. |
Pinout & Package
SN74ALS240A-1DBR uses a 20-pin Small Outline Shrink Plastic (SSOP-DB) package, 7.5 mm × 5.6 mm footprint, 2.0 mm max height, 0.65 mm lead pitch, RoHS-compliant NiPdAu finish, MSL Level-1, tape-and-reel packaging (2000 pcs/reel).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1OE, 2OE | Active-low output enable | Independent control of two 4-bit buffer groups; low = enabled, high = high-Z - enables time-multiplexed bus sharing. |
| 1A1–1A4, 2A1–2A4 | Noninverting data inputs | Eight TTL-compatible inputs accepting 0.8 V/2.0 V thresholds; pnp input structure reduces DC loading on upstream drivers. |
| 1Y1–1Y4, 2Y1–2Y4 | Noninverting 3-state outputs | Eight buffered outputs capable of sinking 48 mA each; high-Z state isolates bus segments during arbitration. |
| VCC, GND | Power supply terminals | Single 5-V supply with dedicated ground pin; decoupling required within 10 mm for noise immunity in high-speed switching. |
Key Features
| Feature | Design Value |
|---|---|
| 48 mA IOL (–1 version) | Supports direct connection to 10+ standard TTL loads or 50-Ω transmission lines without external buffering. |
| Matched OE inputs | Symmetrical active-low OE pins allow synchronized enable/disable of both 4-bit sections for glitch-free bus handoff. |
| pnp input structure | Reduces input current draw to ≤0.1 mA, minimizing loading on clock/address drivers in dense PCB layouts. |
| Fast 3-state transition | tPZL/tPLZ ≤ 18 ns ensures minimal bus contention window during output disable, critical for multi-master arbitration. |
| TTL-compatible thresholds | VIL = 0.8 V and VIH = 2.0 V guarantee interoperability with legacy 74LS, 74ALS, and microprocessor address/data buses. |
Applications
| Memory Address Buffering | Industrial Bus Interface |
|---|---|
Use Scenario: Driving 16-bit address bus in an 80C88-based PLC controller with 32 KB RAM and EPROM expansion. IC Role / Device Role / Timing Role: Noninverting octal buffer providing level translation and fan-out amplification between MPU address pins and memory IC address inputs. Use Value: Eliminates need for discrete transistor arrays; 48 mA sink capability ensures reliable low-level assertion across 10 cm trace lengths with 50 pF load. | Use Scenario: Isolating CAN controller address/data lines from shared system bus during firmware updates. IC Role / Device Role / Timing Role: 3-state bus driver enabling dynamic partitioning of parallel bus segments using OE-controlled enable timing. Use Value: Prevents bus contention during hot-swap programming; sub-20 ns disable time meets ISO 11898-1 arbitration timing constraints. |
| Legacy Microprocessor Support | Test Equipment Signal Conditioning |
Use Scenario: Interfacing Z80 CPU address lines to dual-port RAM in automated test fixture controller. IC Role / Device Role / Timing Role: Octal noninverting buffer with independent OE control for time-multiplexed access to shared memory space. Use Value: Enables simultaneous read/write arbitration via OE sequencing; 2 ns propagation delay preserves setup/hold margins at 8 MHz bus clock. | Use Scenario: Conditioning digital stimulus signals from FPGA pattern generator before applying to DUT address pins. IC Role / Device Role / Timing Role: Signal integrity enhancer adding drive strength and noise margin to high-impedance FPGA outputs. Use Value: Compensates for 15 cm ribbon cable capacitance (≈80 pF); 0.25 V VOL at 24 mA ensures >0.7 V noise margin at receiver inputs. |
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 |
|---|---|---|---|
| SN74ALS240ADBR | Standard version with 24 mA IOL rating (vs. 48 mA for –1 variant); identical pinout and timing. | Suitable for lower-drive applications where bus loading is <5 TTL units; not rated for 48 mA continuous sink. | Select when cost sensitivity outweighs drive requirement; verify IOL margin against actual bus load. |
| SN74AS240ADBR | Faster propagation (1.2–6.5 ns vs. 2–9 ns) and higher ICC (51–75 mA), but same 48 mA IOL and SSOP-DB package. | Better suited for >25 MHz bus speeds; higher power draw requires additional thermal management. | Choose for speed-critical designs where 6.5 ns tPHL meets timing closure; confirm power delivery capability. |
Compared with SN74ALS240ADBR and SN74AS240ADBR, the SN74ALS240A-1DBR uniquely balances enhanced drive (48 mA), moderate speed (2–9 ns), and low static power (14–25 mA disabled), making it optimal for industrial backplane interfaces where reliability and thermal margin outweigh peak frequency needs.
Availability
SN74ALS240A-1DBR is available at Aetrix Electronics and suitable for industrial automation controllers, legacy microprocessor support systems, and test equipment signal conditioning requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant SSOP packaging.
Supply support for SN74ALS240A-1DBR 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 delivering analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The SN74ALS240A-1DBR belongs to TI's legacy 74ALS logic family, engineered for high fan-out, low DC loading, and robust 3-state bus driving in 5-V TTL systems - targeting industrial control, instrumentation, and retro-computing infrastructure.
FAQ
What is the maximum recommended IOL for SN74ALS240A-1DBR?
The SN74ALS240A-1DBR is rated for a maximum low-level output current (IOL) of 48 mA when VCC is maintained between 4.75 V and 5.25 V. This specification applies exclusively to the "–1" variant and is validated per the SDAS214E datasheet. Exceeding this current may cause excessive junction temperature rise or output voltage degradation beyond VOL = 0.5 V.
Does SN74ALS240A-1DBR support mixed-voltage interfacing?
No, SN74ALS240A-1DBR operates strictly at 5-V nominal supply (4.5–5.5 V) and features TTL-compatible input thresholds (VIL = 0.8 V, VIH = 2.0 V). It does not support 3.3-V or 2.5-V logic levels directly; level-shifting circuitry is required for interfacing with lower-voltage devices.
What is the thermal resistance θJA for SN74ALS240A-1DBR in its SSOP-DB package?
The junction-to-ambient thermal resistance (θJA) for SN74ALS240A-1DBR in the SSOP-DB package is 70°C/W, as specified in the absolute maximum ratings table of the SDAS214E datasheet. This value assumes standard JEDEC JESD 51-7 test conditions and must be used with actual power dissipation to calculate junction temperature.
Can SN74ALS240A-1DBR replace SN74ALS240ADBR in existing designs?
Yes, SN74ALS240A-1DBR is pin-compatible and functionally identical to SN74ALS240ADBR, with the sole enhancement being higher IOL (48 mA vs. 24 mA). No PCB changes are required, but designers must verify that the increased sink capability does not overstress downstream components or exceed trace current limits.
What are the key timing parameters for 3-state enable/disable on SN74ALS240A-1DBR?
For SN74ALS240A-1DBR, the 3-state disable time tPZL is 5–26 ns and tPLZ is 3–12 ns; enable time tPHZ is 1–15 ns and tPLZ is 3–12 ns (CL = 50 pF). These define the maximum window during which bus contention could occur - critical for arbitration protocols in multi-driver systems.
SN74ALS240A-1DBR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SSOP (0.209", 5.30mm 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-SSOP
SN74ALS240A-1DBR FAQ
1.How can I place an order for SN74ALS240A-1DBR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS240A-1DBR 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-1DBR reliable?
The price and inventory of SN74ALS240A-1DBR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS240A-1DBR is usually 5 days.
3.What payment methods are accepted for SN74ALS240A-1DBR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS240A-1DBR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS240A-1DBR?
SN74ALS240A-1DBR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS240A-1DBR 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-1DBR?
For technical support, including SN74ALS240A-1DBR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS240A-1DBR requirements.
6.How does Aetrix verify that SN74ALS240A-1DBR is sourced from the original manufacturer or authorized distributors?
All SN74ALS240A-1DBR 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-1DBR meets industry standards.
7.What is the process for return or replacement of SN74ALS240A-1DBR?
All SN74ALS240A-1DBR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS240A-1DBR, 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-1DBR part is unused and in its original packaging.
Return procedure for SN74ALS240A-1DBR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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