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Texas Instruments SN74AS645N
- Part No.:
- SN74AS645N
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74AS645N.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:2,400
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Product details
Overview
SN74AS645N from Texas Instruments is an octal bus transceiver IC with 3-state outputs, designed for asynchronous bidirectional data transfer between A and B buses in industrial control and legacy computing systems. It operates from 4.5 V to 5.5 V, supports 0°C to 70°C ambient temperature, delivers 64 mA low-level output current (IOL), and features direction-control (DIR) and output-enable (OE) logic inputs.
For engineers reviewing the SN74AS645N datasheet, SN74AS645N pinout, SN74AS645N application, or SN74AS645N equivalent, this device is selected for TTL-compatible bus isolation, level-shifting between legacy subsystems, and high-drive 3-state bus interfacing where propagation delay under 12 ns and robust DC drive capability are required.
Technical Context
The SN74AS645N implements true TTL-compatible logic with active-low output enable and unidirectional direction control, enabling deterministic A→B or B→A data flow per cycle. Its bipolar AS (Advanced Schottky) process delivers higher speed and drive strength than ALS variants, with tPLH/tPHL ≤ 9.5 ns at VCC = 5 V and CL = 50 pF.
It uses standard 20-pin PDIP packaging with dual-bus I/O structure: pins 1–8 and 13–20 serve as A1–A8 and B1–B8 bidirectional ports, while DIR (pin 1) and OE (pin 19) govern direction and output state. No internal pull-ups or latching - all control is synchronous with input transitions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - compatible with standard 5 V TTL power rails; no regulation required beyond ±10% tolerance. |
| IOL (Low-Level Output) | 64 mA - drives heavy capacitive loads or multiple TTL inputs without external buffers. |
| tPLH / tPHL | ≤ 9.5 ns - ensures sub-10 ns bus turnaround critical for high-speed parallel interfaces like ISA or custom backplanes. |
| VIH / VIL | 2.0 V / 0.8 V - TTL-compatible input thresholds; interfaces directly with 74LS/74F and microcontroller GPIO without level shifters. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded systems, not extended or industrial temperature operation. |
| ICC (Outputs Low) | 149 mA - reflects full-drive condition; informs thermal design and supply decoupling requirements. |
Pinout & Package
SN74AS645N is supplied in a 20-pin plastic dual in-line package (PDIP-N), 300-mil width, with 0.1-inch lead pitch and through-hole mounting. Pin 1 is marked by a notch or dot at the top-left corner of the package body.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Low = B→A data transfer; High = A→B data transfer; determines signal flow path across transceiver core. |
| 2–9 (A1–A8) | Port A Bidirectional I/O | Connects to first data bus; driven by or receives from A-side system when enabled and directionally aligned. |
| 10 (GND) | Ground Reference | Primary return path for all I/O and supply currents; must be low-impedance connection to minimize noise coupling. |
| 11–18 (B1–B8) | Port B Bidirectional I/O | Connects to second data bus; functions as source or sink depending on DIR state and OE assertion. |
| 19 (OE) | Output Enable Input | Active-low; when High, all A/B ports enter high-impedance state, electrically isolating both buses. |
| 20 (VCC) | Supply Voltage | +5 V nominal power input; requires local 0.1 µF ceramic decoupling adjacent to pin for stable switching operation. |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional Bus Isolation | Enables clean separation of A and B buses during OE high, preventing contention and signal corruption in shared-memory or multi-master systems. |
| 64 mA Output Sink Strength | Drives up to 20 standard TTL loads (or 10 LS-TTL) per output, eliminating need for external driver stages in high-fanout backplane designs. |
| Sub-10 ns Propagation Delay | Supports bus clock rates up to ~100 MHz in point-to-point configurations with controlled trace lengths and proper termination. |
| TTL-Compatible Input Thresholds | Accepts standard 0.8 V / 2.0 V logic levels - interoperable with 74LS, 74F, and most microcontroller I/O without interface logic. |
| True 3-State Output Control | OE and DIR operate independently; outputs go high-Z regardless of DIR state when OE is deasserted, ensuring safe bus arbitration. |
Applications
| Industrial PLC Backplane Interface | Legacy Computer Memory Expansion |
|---|---|
|
Use Scenario: Interfacing CPU address/data bus to modular I/O cards in programmable logic controllers using parallel backplane architecture. IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing data flow between main processor bus and peripheral card slots; enables hot-swap isolation via OE control. Use Value: 64 mA drive supports long traces and multiple card stubs; sub-10 ns delay maintains timing margin across 8-bit parallel transfers at 8–12 MHz. |
Use Scenario: Adding RAM or ROM expansion modules to 1980s-era 8-bit microcomputers (e.g., Z80 or 6502-based systems) with shared address/data buses. IC Role / Device Role / Timing Role: Direction-controlled buffer isolating expansion memory from main system bus during read/write cycles; DIR selects memory vs. I/O access path. Use Value: TTL-compatible thresholds ensure seamless integration with vintage logic families; 3-state outputs prevent bus contention during memory wait states. |
| Test Equipment Digital I/O Subsystem | Automated Manufacturing Fixture Controller |
|
Use Scenario: Building configurable digital stimulus/response hardware for functional testing of PCB assemblies, requiring programmable bus direction and isolation. IC Role / Device Role / Timing Role: Reconfigurable transceiver enabling test controller to drive or monitor DUT signals on same physical lines - DIR sets mode, OE enables/disables. Use Value: High sink current allows direct driving of LEDs, relays, or optocouplers; fast switching supports pattern generation at >50 MHz burst rates. |
Use Scenario: Controlling pneumatic valves, solenoids, and sensors in factory automation fixtures where microcontroller GPIO count is limited. IC Role / Device Role / Timing Role: Parallel I/O expander providing 16 bidirectional bits (via two SN74AS645N devices) with direction flexibility per byte for mixed input/output sensor/actuator interfaces. Use Value: Robust 64 mA per output eliminates need for discrete transistor drivers; OE allows dynamic reconfiguration without software overhead. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bidirectional bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS645AN | ALS variant: lower IOL (24 mA), slower tPLH/tPHL (≤10 ns), reduced ICC (55 mA max), wider VIH/VIL margins (2.0 V / 0.7 V). | Suitable for lower-power, noise-immune legacy systems where drive strength and speed are secondary to static noise margin. | Select SN74ALS645AN only if design prioritizes lower power and higher noise immunity over drive capability and speed. |
| 74F245N | F-family: 35 mA IOL, 3.5 ns typical tPLH/tPHL, 5 V-only operation, higher ICC (110 mA), tighter VIH/VIL (2.0 V / 0.8 V). | Better suited for high-speed, low-latency interconnects where propagation delay dominates over drive strength. | Choose 74F245N when sub-5 ns timing is mandatory and load drive ≤35 mA suffices; avoid if interfacing heavy TTL loads. |
Compared with SN74ALS645AN and 74F245N, SN74AS645N uniquely balances high drive (64 mA), moderate speed (≤9.5 ns), and commercial-temperature reliability - making it optimal for industrial backplanes and legacy expansion where both fanout and timing matter.
Availability
SN74AS645N is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy computer expansion modules, automated test equipment, and factory fixture controllers requiring stable component supply and long-term obsolescence management.
Supply support for SN74AS645N 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 solutions for industrial, automotive, and communications markets.
The SN74AS645N belongs to TI's legacy 74AS logic family - engineered for high-speed, high-drive TTL-compatible bus interfacing in commercial-grade embedded and control systems.
FAQ
What is the maximum operating temperature range for SN74AS645N?
The SN74AS645N is characterized for operation from 0°C to 70°C - a commercial temperature grade. It is not rated for extended industrial (–40°C to 85°C) or military (–55°C to 125°C) ranges. Operation outside 0°C–70°C may result in parametric failure or reduced reliability. Always verify ambient and junction temperature limits in thermal design for SN74AS645N.
Does SN74AS645N support bidirectional data flow on the same pins?
Yes, SN74AS645N provides true bidirectional I/O on both A1–A8 and B1–B8 pins. Data flows from A to B when DIR = High and OE = Low, or from B to A when DIR = Low and OE = Low. When OE = High, all A and B pins enter high-impedance state regardless of DIR, enabling bus isolation - a core function of SN74AS645N.
What is the recommended supply decoupling for SN74AS645N?
TI recommends a 0.1 µF ceramic capacitor placed as close as possible to the VCC (pin 20) and GND (pin 10) pins of SN74AS645N. For systems with multiple SN74AS645N devices or high switching activity, add a bulk 4.7 µF–10 µF tantalum or aluminum electrolytic capacitor near the power entry point. This ensures stable VCC during fast 64 mA output transitions in SN74AS645N.
Can SN74AS645N replace SN74LS245 in existing designs?
SN74AS645N can replace SN74LS245 in many cases due to identical pinout, function, and voltage compatibility, but with key differences: SN74AS645N offers 64 mA IOL (vs. 24 mA for LS245), faster propagation (≤9.5 ns vs. ≤25 ns), and higher ICC. Verify that the increased drive and speed do not cause overshoot or ground bounce in the existing layout before substituting SN74AS645N.
Is SN74AS645N RoHS compliant?
Yes, SN74AS645N is RoHS compliant (lead-free finish: NiPdAu/NiPdAu over Cu, per TI's Package Option Addendum). The part marking "SN74AS645N" appears on the top surface, and the device meets JEDEC J-STD-020 moisture sensitivity Level 1 (unlimited floor life at ≤30°C/60% RH). Full compliance documentation is available from TI for SN74AS645N.
SN74AS645N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AS
- Package/Case:
- 20-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- Transceiver, Non-Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 8
- Input Type:
- -
- Output Type:
- 3-State
- Current - Output High, Low:
- 15mA, 64mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74AS645N FAQ
1.How can I place an order for SN74AS645N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS645N 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 SN74AS645N reliable?
The price and inventory of SN74AS645N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS645N is usually 5 days.
3.What payment methods are accepted for SN74AS645N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AS645N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AS645N?
SN74AS645N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS645N 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 SN74AS645N?
For technical support, including SN74AS645N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS645N requirements.
6.How does Aetrix verify that SN74AS645N is sourced from the original manufacturer or authorized distributors?
All SN74AS645N 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 SN74AS645N meets industry standards.
7.What is the process for return or replacement of SN74AS645N?
All SN74AS645N units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS645N, 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 SN74AS645N part is unused and in its original packaging.
Return procedure for SN74AS645N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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