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Texas Instruments SN74LS444DW
- Part No.:
- SN74LS444DW
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- -
- Datasheet:
-
SN74LS444DW.pdf
- Description:
- BUS EXCHANGER, LS SERIES
- Quantity:
- Payment:
- Shipping:
Inventory:436
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Product details
Overview
SN74LS444DW from Texas Instruments is a quadruple tridirectional bus transceiver in a 24-pin SOIC package, featuring three-state outputs, TTL-compatible logic levels, and ±20 mA output drive capability. It enables bidirectional data flow control between two 4-bit buses in legacy industrial control and test equipment systems.
For engineers reviewing the SN74LS444DW datasheet, SN74LS444DW pinout, SN74LS444DW application, or SN74LS444DW equivalent, key selection considerations include tridirectional control timing (tEN, tDIS), bus hold immunity, DC electrical limits (VOH/VOL, IOH/IOL), and compatibility with LS-TTL system voltage rails.
Technical Context
The SN74LS444DW implements four independent tridirectional data paths, each with separate direction (DIR) and output-enable (OE) controls. Each channel supports bidirectional data transfer without external logic, with propagation delays of 15 ns typical (A→B) and 20 ns typical (B→A) at VCC = 5 V.
It operates strictly within the 4.75 V to 5.25 V supply range and draws 38 mA maximum ICC. Input thresholds align with standard LS-TTL (VIH = 2.0 V min, VIL = 0.8 V max), and outputs meet LS-TTL sink/source drive specifications under load.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Quadruple tridirectional bus transceiver with independent DIR/OE per channel |
| Supply Voltage | 4.75 V to 5.25 V - ensures stable operation in legacy 5 V TTL systems |
| Propagation Delay | 15 ns (A→B), 20 ns (B→A) - defines maximum synchronous bus clock rate |
| Output Drive | ±20 mA - sufficient to drive 20 LS-TTL loads or terminate unterminated stubs |
| Input Thresholds | VIL ≤ 0.8 V, VIH ≥ 2.0 V - guarantees noise margin against LS-TTL logic swings |
| Operating Temperature | 0 °C to +70 °C - rated for commercial-grade embedded and instrumentation use |
Pinout & Package
SN74LS444DW uses a 24-pin SOIC (Small Outline Integrated Circuit) package with 300-mil body width and standard JEDEC MS-013AC footprint. Pin spacing is 0.050 inch (1.27 mm), compatible with automated SMT placement.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2, 3, 4 | A-side inputs/outputs | Bidirectional data terminals for Bus A (A1–A4) |
| 5, 6, 7, 8 | B-side inputs/outputs | Bidirectional data terminals for Bus B (B1–B4) |
| 9, 11, 13, 15 | Direction controls (DIR1–DIR4) | High = A→B transfer; Low = B→A transfer per channel |
| 10, 12, 14, 16 | Output enables (OE1–OE4) | Low = active output; High = high-impedance state |
| 24 | VCC | +5 V power supply connection |
| 12 | GND | Ground reference for all logic and I/O |
Key Features
| Feature | Design Value |
|---|---|
| Independent per-channel control | Four DIR/OE pairs enable selective bus arbitration without global gating |
| Tridirectional operation | Eliminates need for external direction logic or dual transceivers in multipoint bus topologies |
| TTL-compatible interface | Direct drop-in replacement for LS-TTL bus interfaces without level-shifting circuitry |
| Three-state outputs | Enables shared-bus contention avoidance with fast disable time (tDIS = 15 ns max) |
Applications
| Industrial PLC Backplane | Legacy Test Equipment Interface |
|---|---|
Use Scenario: Bidirectional data exchange between CPU module and I/O expansion cards on a 4-bit parallel backplane. IC Role / Device Role / Timing Role: Bus transceiver managing direction-controlled data flow between master and slave slots. Use Value: Enables deterministic read/write handshaking with sub-20 ns channel switching and LS-TTL signal integrity. |
Use Scenario: Interfacing microcontroller-based test head with DUT-specific adapter boards using shared 4-bit control/data lines. IC Role / Device Role / Timing Role: Tridirectional buffer isolating and routing control signals during test sequence execution. Use Value: Supports dynamic reconfiguration of signal direction without firmware overhead or external glue logic. |
| Computer Terminal Expansion | Embedded Instrumentation Subsystem |
Use Scenario: Adding serial-to-parallel conversion capability to vintage ASCII terminal hardware via parallel port extension. IC Role / Device Role / Timing Role: Data path controller synchronizing keyboard scan matrix and display refresh buffers. Use Value: Maintains tight timing alignment across multiple 4-bit data lanes with matched propagation delay. |
Use Scenario: Isolating sensor acquisition bus from processor bus in compact data loggers with limited PCB real estate. IC Role / Device Role / Timing Role: Direction-managed bus bridge preventing signal contention during simultaneous ADC read and DAC write cycles. Use Value: Reduces component count by replacing discrete direction logic and dual transceivers with single IC. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar tridirectional bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS245N | Octal unidirectional transceiver with single-direction control; no per-channel DIR pins | Requires external logic for bidirectional operation; suited for fixed-direction 8-bit buses | Choose when full 8-bit throughput is needed and direction is static or globally controlled |
| SN74ALS444DW | ALS-family version with 2× faster propagation (8 ns A→B), lower ICC (15 mA), but tighter VCC tolerance (4.5–5.5 V) | Higher speed and lower power, but reduced noise margin on VIL/VIH thresholds | Prefer for new designs requiring improved timing margin and reduced power, provided voltage regulation is tight |
Compared with SN74LS444DW, SN74LS245N simplifies control at the cost of flexibility in dynamic bus arbitration, while SN74ALS444DW delivers measurable speed and efficiency gains but demands stricter supply regulation and may require layout review for noise coupling.
Availability
SN74LS444DW is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy test equipment interfaces, and embedded instrumentation subsystems requiring stable component supply and long-term obsolescence management.
Supply support for SN74LS444DW 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 for industrial, automotive, and communications markets.
The SN74LS444DW belongs to TI's legacy 74LS logic family, designed specifically for reliable, low-cost bidirectional bus interfacing in 5 V TTL systems deployed in industrial control and test instrumentation.
FAQ
What is the function of the DIR and OE pins on the SN74LS444DW?
The SN74LS444DW has four independent DIR (direction) and OE (output enable) pins - one pair per channel. DIR determines data flow direction (high = A→B, low = B→A); OE controls output state (low = active, high = high-Z). This allows granular bus arbitration without global control signals. The SN74LS444DW supports true tridirectional operation per channel, unlike octal transceivers with shared controls.
Does the SN74LS444DW support hot insertion or live bus swapping?
No, the SN74LS444DW does not support hot insertion. Its inputs lack bus-hold or Schmitt-trigger circuitry, and its outputs do not feature current-limited or slew-rate-controlled drivers. Applying signals before VCC stabilization risks latch-up or parametric shift. System-level hot-swap capability requires external protection circuitry. The SN74LS444DW is intended for powered-system bus interconnect only.
Can the SN74LS444DW be used with 3.3 V logic systems?
No, the SN74LS444DW is not compatible with 3.3 V logic. It requires 4.75–5.25 V VCC, and its input thresholds (VIL ≤ 0.8 V, VIH ≥ 2.0 V) are defined for 5 V TTL levels. Driving it from 3.3 V sources risks marginal VIH recognition; driving 3.3 V receivers with its 5 V outputs violates absolute maximum ratings. Level translation is mandatory. The SN74LS444DW must operate in dedicated 5 V domains.
What is the maximum clock rate supported by the SN74LS444DW in a synchronous bus application?
The SN74LS444DW does not include internal clocking - it is asynchronous. Maximum usable data rate depends on propagation delay (15–20 ns) and system setup/hold timing. For reliable operation with LS-TTL loads, practical bus cycle times are ≥ 50 ns (20 MHz effective), assuming clean edges and minimal skew. The SN74LS444DW is typically used in slower control-plane buses rather than high-speed data paths.
Is there a surface-mount alternative to the SN74LS444DW with identical pinout and function?
Yes - the SN74LS444DWR (tape-and-reel SOIC-24) and SN74LS444DGGR (TSSOP-24) share identical logic function, pinout, and DC/AC specifications with the SN74LS444DW. Both are manufactured by Texas Instruments and fully interchangeable in layout, though TSSOP requires reflow profile adjustment. The SN74LS444DW remains the standard SOIC variant for through-hole prototyping and legacy rework.
SN74LS444DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Type:
- -
- Circuit:
- -
- Independent Circuits:
- -
- Current - Output High, Low:
- -
- Voltage Supply Source:
- -
- Voltage - Supply:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- -
- Supplier Device Package:
- -
SN74LS444DW FAQ
1.How can I place an order for SN74LS444DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS444DW 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 SN74LS444DW reliable?
The price and inventory of SN74LS444DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS444DW is usually 5 days.
3.What payment methods are accepted for SN74LS444DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS444DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS444DW?
SN74LS444DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS444DW 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 SN74LS444DW?
For technical support, including SN74LS444DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS444DW requirements.
6.How does Aetrix verify that SN74LS444DW is sourced from the original manufacturer or authorized distributors?
All SN74LS444DW 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 SN74LS444DW meets industry standards.
7.What is the process for return or replacement of SN74LS444DW?
All SN74LS444DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS444DW, 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 SN74LS444DW part is unused and in its original packaging.
Return procedure for SN74LS444DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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