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Texas Instruments SN74ALS645ADB
- Part No.:
- SN74ALS645ADB
- Manufacturer:
- Texas Instruments
- Package:
- -
- Datasheet:
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SN74ALS645ADB.pdf
- Description:
- BUS TRANSCEIVER
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Product details
Overview
SN74ALS645ADB from Fairchild Semiconductor is an octal bus transceiver IC designed for asynchronous bidirectional data transfer between two 8-bit buses. It features direction control (DIR) and output enable (G) inputs, supports ±24 mA output drive, operates at VCC = 4.5–5.5 V, and delivers propagation delays as low as 3 ns with 50 pF load-used in legacy TTL-based system interconnects and backplane data routing.
For engineers reviewing the SN74ALS645ADB datasheet, SN74ALS645ADB pinout, SN74ALS645ADB application, or SN74ALS645ADB equivalent, key selection criteria include bidirectional bus isolation timing, 3-STATE output compatibility with ALS logic families, DC drive capability, thermal derating in SOIC-20 packages, and legacy industrial control board integration requirements.
Technical Context
The SN74ALS645ADB implements dual 8-bit bidirectional data paths controlled by a single DIR input and a common output enable (G). Its PNP-input structure reduces input loading, and switching performance is guaranteed across 0°C to +70°C and full VCC range (4.5–5.5 V).
All I/O ports support true 3-STATE outputs with IOH = −15 mA and IOL = 24 mA, and propagation delays (tPLH/tPHL) are specified at CL = 50 pF with R1 = R2 = 500 Ω, enabling reliable timing in synchronous and asynchronous bus architectures.
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 margin for ripple or drop. |
| IOL / IOH | 24 mA / −15 mA - Supports direct driving of multiple TTL loads without external buffers in legacy systems. |
| tPLH / tPHL | 3 ns to 10 ns - Enables high-speed bus handshaking in 8-bit microprocessor peripheral interfaces. |
| VIH / VIL | 2.0 V / 0.8 V - Matches ALS family input thresholds for noise-immune level translation between compatible logic families. |
| ICC (Outputs HIGH) | 30–45 mA - Defines static power budget per device in dense backplane or motherboard bus driver arrays. |
| Operating Temp | 0°C to +70°C - Specifies commercial-grade temperature envelope for non-automotive industrial control applications. |
Pinout & Package
SN74ALS645ADB is housed in a 20-lead Small Outline Integrated Circuit (SOIC) package, JEDEC MS-013 compliant, 0.300-inch body width, surface-mountable with standard reflow profiles.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A1–A8 | Input/Output Port A | 8-bit bidirectional data terminal connected to first bus segment; 3-STATE when G = HIGH. |
| B1–B8 | Input/Output Port B | 8-bit bidirectional data terminal connected to second bus segment; direction determined by DIR. |
| G | Output Enable | Active-LOW control: G = LOW enables transceiver; G = HIGH forces all A/B pins into high-impedance state. |
| DIR | Direction Control | When G = LOW, DIR = LOW routes B→A; DIR = HIGH routes A→B - no internal latching. |
| VCC | Power Supply | +5 V nominal supply connection; decoupling required within 10 mm of pin per ALS design guidelines. |
| GND | Ground Reference | Common return path for all I/O and supply currents; must be low-inductance plane for signal integrity. |
Key Features
| Feature | Design Value |
|---|---|
| ALS Schottky TTL Process | Enables higher speed and lower power than standard TTL while maintaining pin-and-function compatibility with 74LS/74ALS families. |
| PNP Input Structure | Reduces input current loading (IIH ≤ 20 µA, IIL ≥ −100 µA), easing fanout constraints on upstream drivers. |
| Guaranteed Switching at Full Range | Specified timing and DC parameters validated across 0°C to +70°C and 4.5–5.5 V - eliminates derating calculations for commercial designs. |
| 50 pF Load Timing Spec | Propagation and enable/disable delays tested under standardized capacitive load - enables accurate timing margin analysis in PCB trace environments. |
Applications
| Industrial PLC Backplanes | Legacy Microprocessor Peripherals |
|---|---|
Use Scenario: Isolating and routing 8-bit data between CPU and I/O expansion modules in programmable logic controller racks. IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing address/data multiplexing and direction-controlled data flow between master and slave slots. Use Value: Enables hot-swap-safe bus isolation via G control and meets strict 10 ns max propagation delay for deterministic scan-cycle timing. | Use Scenario: Interfacing Z80 or 8085-based systems with external memory-mapped peripherals using shared data buses. IC Role / Device Role / Timing Role: Directionally configurable data bridge allowing CPU-initiated reads/writes without bus contention or latch arbitration. Use Value: Delivers 24 mA sink current to drive legacy TTL memory chips directly, eliminating need for discrete buffer stages. |
| Test Equipment Data Paths | Avionics Maintenance Interfaces |
Use Scenario: Routing stimulus/response data between FPGA-based pattern generators and DUT interface connectors in automated test systems. IC Role / Device Role / Timing Role: 3-STATE-enabled bus repeater synchronizing asynchronous test vectors across isolated voltage domains. Use Value: Provides sub-10 ns propagation and <20 ns enable/disable transitions for precise timing alignment in high-speed digital test fixtures. | Use Scenario: Supporting ground-based diagnostic communication between maintenance laptops and avionics line-replaceable units (LRUs) via MIL-STD-1553 auxiliary buses. IC Role / Device Role / Timing Role: Level-translating and isolating bidirectional command/status data between 5 V laptop UARTs and LRU logic subsystems. Use Value: Ensures robust operation at 70°C ambient and withstands transient overvoltage up to 7 V on control inputs per Absolute Maximum Ratings. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS645N | Slower propagation (15–25 ns), lower drive (IOL = 20 mA), higher ICC (55–75 mA); LS-family process. | Compatible in static 5 V systems but unsuitable for timing-critical paths requiring <10 ns delay. | Choose when cost sensitivity outweighs speed and power targets; verify timing slack in critical paths. |
| SN74F645N | Faster propagation (2.5–8 ns), higher drive (IOL = 32 mA), higher ICC (60–90 mA); F-family process. | Supports higher-frequency bus cycles but increases thermal load and EMI risk in dense layouts. | Prefer where sub-8 ns delay is mandatory and board-level thermal management is confirmed. |
Compared with SN74LS645N and SN74F645N, the SN74ALS645ADB delivers optimal balance of speed (3–10 ns), drive strength (24 mA), and power efficiency (45 mA ICC), making it ideal for mid-performance industrial backplanes where ALS compatibility and thermal headroom are prioritized.
Availability
SN74ALS645ADB is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy microprocessor peripherals, and test equipment data paths requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS645ADB 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
Fairchild Semiconductor was a U.S.-based semiconductor company specializing in analog and mixed-signal ICs, power management, and logic devices before its acquisition by ON Semiconductor in 2016.
The SN74ALS645ADB belongs to Fairchild's 74ALS logic family, engineered for enhanced speed-power trade-offs in industrial and instrumentation systems requiring reliable 5 V TTL-compatible bus interfacing.
FAQ
What is the maximum operating temperature for the SN74ALS645ADB?
The SN74ALS645ADB is rated for operation from 0°C to +70°C ambient temperature, consistent with commercial-grade TTL logic specifications. This range is defined in the Recommended Operating Conditions table and validated across all electrical parameters including propagation delay and output drive. Exceeding +70°C may cause timing violations or increased ICC drift. The SN74ALS645ADB does not support extended or industrial temperature grades.
Does the SN74ALS645ADB support true bidirectional data flow without external logic?
Yes, the SN74ALS645ADB supports true bidirectional data flow using only its DIR and G inputs - no external latches or control logic required. When G = LOW, setting DIR = LOW enables B→A transfer; DIR = HIGH enables A→B transfer. Both directions operate concurrently on separate 8-bit paths, and the 3-STATE outputs ensure clean bus isolation during direction changes.
What is the recommended decoupling for the SN74ALS645ADB?
Each SN74ALS645ADB requires a minimum 0.1 µF ceramic capacitor placed within 10 mm of the VCC pin and connected to a low-inductance ground plane. For boards with multiple SN74ALS645ADB devices, add one 4.7 µF tantalum or aluminum electrolytic capacitor per 5–10 devices near the power entry point. This mitigates simultaneous switching noise and maintains VCC stability during 24 mA output transitions.
Can the SN74ALS645ADB be used with 3.3 V logic systems?
No, the SN74ALS645ADB is not 3.3 V compatible. Its absolute maximum input voltage on control inputs is 7 V, but VIH = 2.0 V and VIL = 0.8 V are specified only for VCC = 4.5–5.5 V operation. Driving DIR or G from 3.3 V logic risks marginal HIGH-level recognition and violates recommended operating conditions. Use level translators or 5 V-tolerant interface ICs when interfacing with 3.3 V systems.
Is the SN74ALS645ADB pin-compatible with other 74-series octal transceivers?
Yes, the SN74ALS645ADB shares identical pinout and function mapping with SN74LS645, SN74F645, and DM74ALS645A in the same 20-pin SOIC or PDIP package. All feature A1–A8, B1–B8, DIR, G, VCC, and GND in identical positions. However, timing, drive strength, and power consumption differ - verify timing margins and thermal design when substituting across families.
SN74ALS645ADB Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- -
- Number of Elements:
- -
- Number of Bits per Element:
- -
- Input Type:
- -
- Output Type:
- -
- Current - Output High, Low:
- -
- Voltage - Supply:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- -
- Supplier Device Package:
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SN74ALS645ADB FAQ
1.How can I place an order for SN74ALS645ADB through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS645ADB 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 SN74ALS645ADB reliable?
The price and inventory of SN74ALS645ADB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS645ADB is usually 5 days.
3.What payment methods are accepted for SN74ALS645ADB?
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4.How is shipping managed for SN74ALS645ADB?
SN74ALS645ADB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS645ADB 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 SN74ALS645ADB?
For technical support, including SN74ALS645ADB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS645ADB requirements.
6.How does Aetrix verify that SN74ALS645ADB is sourced from the original manufacturer or authorized distributors?
All SN74ALS645ADB 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 SN74ALS645ADB meets industry standards.
7.What is the process for return or replacement of SN74ALS645ADB?
All SN74ALS645ADB units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS645ADB, 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 SN74ALS645ADB part is unused and in its original packaging.
Return procedure for SN74ALS645ADB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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