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Texas Instruments SN74LS644-1N
- Part No.:
- SN74LS644-1N
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS644-1N.pdf
- Description:
- IC TXRX INVERT 5.25V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:1,924
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Product details
Overview
SN74LS644-1N from Texas Instruments is an octal bus transceiver with open-collector outputs, designed for bidirectional data flow control in TTL-level parallel bus systems. It features 8-bit non-inverting data paths, independent output-enable (OE) and direction (DIR) controls, and supports logic-level translation between 5 V TTL buses. It is used in industrial backplane interfaces and legacy microprocessor system expansion.
For engineers reviewing the SN74LS644-1N datasheet, SN74LS644-1N pinout, SN74LS644-1N application, or SN74LS644-1N equivalent, key selection criteria include open-collector drive capability, DIR/OE logic polarity, propagation delay under load, DC output voltage limits, and compatibility with LS-TTL input thresholds and bus termination schemes.
Technical Context
The SN74LS644-1N implements two independent 4-bit sections (A↔B), each with separate DIR and OE inputs controlling bidirectional signal flow. Its open-collector outputs allow wired-AND bus arbitration and level shifting when pulled up to external voltages up to 15 V.
It operates strictly within the 5 V ±5% supply range and meets standard LS-TTL input thresholds (VIH = 2.0 V min, VIL = 0.8 V max). Propagation delays are specified at 25 ns (max) for both A→B and B→A directions under 15 pF/400 Ω load conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Octal non-inverting bus transceiver with open-collector outputs |
| Supply Voltage | 4.75 V to 5.25 V - ensures compatibility with standard TTL power rails and noise margin compliance |
| Propagation Delay | 25 ns max (A→B or B→A) - defines maximum clock-to-data timing budget in synchronous bus designs |
| Output Drive | Open-collector, IOH = 0 mA, IOL = 24 mA - enables wired-AND bus sharing and external pull-up flexibility up to 15 V |
| Input Thresholds | VIH = 2.0 V min, VIL = 0.8 V max - guarantees reliable recognition of LS-TTL logic levels |
| Operating Temperature | 0 °C to +70 °C - validated for commercial-grade embedded and instrumentation applications |
| Package | 20-pin PDIP (N) - through-hole mounting compatible with legacy prototyping and repair workflows |
Pinout & Package
SN74LS644-1N is housed in a 20-pin plastic dual in-line package (PDIP) with 0.3-inch body width and standard 0.1-inch pin pitch. Pin 1 is marked by a notch or dot at the top-left corner.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR1) | Direction control - Section 1 | High = A→B data flow; Low = B→A - enables independent bidirectional routing per 4-bit group |
| 2–5 (A1–A4) | Data inputs/outputs - Section 1 A-side | Connected to local bus or peripheral; open-collector - requires external pull-up for logic HIGH |
| 6–9 (B1–B4) | Data inputs/outputs - Section 1 B-side | Connected to system bus or backplane; open-collector - shares bus line with other OC devices |
| 10 (GND) | Ground reference | Common return path for all internal logic and output current sinks |
| 11–14 (B5–B8) | Data inputs/outputs - Section 2 B-side | Second 4-bit channel for expanded bus width or isolated subsystem interface |
| 15 (DIR2) | Direction control - Section 2 | Independent of DIR1 - allows asymmetric data flow (e.g., A→B on ch1, B→A on ch2) |
| 16–19 (A5–A8) | Data inputs/outputs - Section 2 A-side | Paired with B5–B8; identical electrical behavior to pins 2–5 |
| 20 (VCC) | Positive supply | +5 V DC power rail - must be decoupled locally with 0.1 µF ceramic capacitor |
Key Features
| Feature | Design Value |
|---|---|
| Two independent 4-bit bidirectional channels | Enables split-bus architectures without external gating - reduces PCB routing complexity |
| Open-collector outputs with 24 mA sink capability | Supports wired-AND arbitration and mixed-voltage bus interfacing (e.g., 5 V logic driving 12 V display bus) |
| Separate DIR and OE controls per section | Allows fine-grained bus ownership management - e.g., hold one channel while transferring on the other |
| Matched propagation delays (A→B ≈ B→A) | Ensures deterministic timing in full-duplex or time-multiplexed bus protocols |
| LS-TTL compatible input thresholds and drive strength | Direct drop-in replacement for SN74LS245 in legacy designs requiring open-collector flexibility |
Applications
| Industrial Backplane Interface | Legacy Microprocessor Expansion |
|---|---|
Use Scenario: Interfacing multiple 8-bit peripheral cards to a shared ISA-style backplane with active-low enable signaling. IC Role / Device Role / Timing Role: Bidirectional data buffer with open-collector outputs enabling bus contention resolution via external pull-ups and priority encoding. Use Value: Eliminates need for discrete AND gates or additional bus controllers - simplifies card-edge connector design and reduces component count. | Use Scenario: Adding external RAM or I/O ports to Z80 or 8085-based systems where bus loading and direction control are critical. IC Role / Device Role / Timing Role: Level-shifting and direction-controlled data conduit between CPU address/data bus and peripheral memory space. Use Value: Provides precise timing alignment (25 ns max delay) and robust noise immunity (0.8 V/2.0 V thresholds) required for stable 4–6 MHz CPU operation. |
| Test Equipment Bus Arbitration | Programmable Logic Controller (PLC) I/O Module |
Use Scenario: Sharing a common diagnostic bus among multiple DUT (device-under-test) handlers in automated test systems. IC Role / Device Role / Timing Role: Wired-AND bus transceiver allowing multiple handlers to assert status flags simultaneously without hardware conflict. Use Value: Enables real-time fault flag aggregation without arbitration logic - reduces test cycle latency and firmware overhead. | Use Scenario: Isolating field I/O signals from the main controller bus in DIN-rail mounted PLC modules operating in electrically noisy factory environments. IC Role / Device Role / Timing Role: Robust, low-speed bidirectional interface with high noise immunity and open-collector fail-safe output behavior. Use Value: Prevents bus lockup during transient faults - outputs default to high-impedance when powered down or disabled, avoiding signal contention. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS245N | Tri-state (not open-collector) outputs; no wired-AND capability; 35 ns max propagation delay | Requires external bus contention logic; unsuitable for mixed-voltage or wired-logic bus topologies | Select when strict tri-state isolation is needed and bus arbitration is handled elsewhere |
| SN74LS642-1N | Same open-collector architecture but with inverting data paths (A→¬B, B→¬A); identical pinout and timing | Requires logic inversion in upstream/downstream circuitry - adds gate delay and layout complexity | Select only if system-level signal polarity aligns with inverted data flow; otherwise use SN74LS644-1N for direct mapping |
Compared with SN74LS245N and SN74LS642-1N, the SN74LS644-1N uniquely delivers non-inverting open-collector functionality in a pin-compatible 20-pin PDIP package - making it the only choice for legacy designs requiring both polarity fidelity and wired-logic bus sharing without redesign.
Availability
SN74LS644-1N is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy microprocessor expansion, test equipment bus arbitration, and programmable logic controller (PLC) I/O modules requiring stable component supply across long-lifecycle production programs.
Supply support for SN74LS644-1N 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 global semiconductor leader founded in 1930, specializing in analog, embedded processing, and logic ICs with deep heritage in TTL and LS-TTL families.
The SN74LS644-1N belongs to TI's 74LS logic series - engineered for reliability and interoperability in industrial control, instrumentation, and retro-computing systems where backward compatibility and deterministic timing are essential.
FAQ
What is the primary function of the SN74LS644-1N in a digital system?
The SN74LS644-1N serves as an octal non-inverting bus transceiver with open-collector outputs, enabling bidirectional data transfer between two 8-bit buses while supporting wired-AND bus arbitration. Its DIR and OE controls allow precise management of data flow direction and bus access timing in legacy TTL systems. The SN74LS644-1N is especially valuable where bus contention avoidance and mixed-voltage interfacing are required without adding discrete logic.
Does the SN74LS644-1N support 3.3 V logic levels?
No, the SN74LS644-1N is a standard LS-TTL device designed exclusively for 5 V operation (4.75–5.25 V). Its input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and output characteristics are specified only for 5 V supply. Direct connection to 3.3 V logic may result in unreliable switching or excessive input current; level-shifting circuitry is required for interoperability. The SN74LS644-1N does not include internal voltage translation.
Can the SN74LS644-1N replace the SN74LS245N in an existing design?
Not directly - while both are octal transceivers in 20-pin PDIP packages, the SN74LS644-1N has open-collector outputs versus the tri-state outputs of the SN74LS245N. Replacing SN74LS245N with SN74LS644-1N requires adding external pull-up resistors and verifying bus contention behavior. The SN74LS644-1N also has faster propagation (25 ns vs. 35 ns) and different DIR/OE logic polarities. Functional equivalence depends on whether wired-AND capability is needed.
What is the maximum sink current per output pin on the SN74LS644-1N?
Each open-collector output of the SN74LS644-1N is rated for a maximum continuous sink current of 24 mA at VCC = 5 V and TA = 25 °C. This rating applies under steady-state DC conditions; transient current spikes must remain within SOA limits. Exceeding 24 mA risks parametric shift or long-term reliability degradation. The SN74LS644-1N datasheet specifies this value explicitly in the "Recommended Operating Conditions" table.
Is the SN74LS644-1N RoHS compliant?
Yes, the SN74LS644-1N is RoHS compliant, as confirmed by Texas Instruments' packaging addendum: lead finish is NiPdAu (NIPDAU), and RoHS status is marked "Yes". It meets EU Directive 2011/65/EU requirements for restricted substances. The SN74LS644-1N is suitable for commercial applications requiring environmental compliance without exemptions.
SN74LS644-1N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 20-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- Transceiver, Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 8
- Input Type:
- -
- Output Type:
- Open Collector
- Current - Output High, Low:
- 100µA, 24mA
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74LS644-1N FAQ
1.How can I place an order for SN74LS644-1N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS644-1N 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 SN74LS644-1N reliable?
The price and inventory of SN74LS644-1N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS644-1N is usually 5 days.
3.What payment methods are accepted for SN74LS644-1N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS644-1N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS644-1N?
SN74LS644-1N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS644-1N 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 SN74LS644-1N?
For technical support, including SN74LS644-1N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS644-1N requirements.
6.How does Aetrix verify that SN74LS644-1N is sourced from the original manufacturer or authorized distributors?
All SN74LS644-1N 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 SN74LS644-1N meets industry standards.
7.What is the process for return or replacement of SN74LS644-1N?
All SN74LS644-1N units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS644-1N, 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 SN74LS644-1N part is unused and in its original packaging.
Return procedure for SN74LS644-1N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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