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Texas Instruments SN74HCT645N
- Part No.:
- SN74HCT645N
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74HCT645N.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:735
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Product details
Overview
SN74HCT645N from Texas Instruments is an octal bus transceiver IC designed for asynchronous two-way data communication between parallel buses in 5-V digital systems. It features bidirectional data flow controlled by DIR, 3-state outputs enabled/disabled by OE, ±6-mA drive strength at 5 V, 14-ns typical propagation delay, and TTL-compatible inputs. It is used in microcontroller peripheral interfacing, memory expansion, and system-level bus isolation.
For engineers reviewing the SN74HCT645N datasheet, SN74HCT645N pinout, SN74HCT645N application, or SN74HCT645N equivalent, key selection criteria include direction-control logic behavior, 3-state output timing (ten/tdis), high-current drive capability for LSTTL loads, operating voltage range (4.5–5.5 V), and PDIP-20 package compatibility with legacy through-hole designs.
Technical Context
The SN74HCT645N implements dual 8-bit bidirectional bus transceivers with independent direction (DIR) and output-enable (OE) control signals. Its logic architecture supports A→B or B→A data transfer based on DIR level, while OE asserts high-impedance state on both A and B ports simultaneously.
It uses HCMOS-compatible input thresholds (VIH = 2 V min, VIL = 0.8 V max) and delivers rail-to-rail CMOS output swing. The device operates strictly within 4.5–5.5 V, draws ≤80 µA ICC, and maintains specified timing across −40°C to +85°C ambient temperature.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 4.5 V to 5.5 V - ensures compatibility with standard 5-V TTL/CMOS logic rails and noise margin compliance. |
| Propagation Delay | 14 ns typ at 5.5 V - enables reliable operation in high-speed 5-V bus systems up to ~35 MHz clock-equivalent rates. |
| Output Drive | ±6 mA at 5 V - drives up to 15 LSTTL loads directly without buffering, reducing component count in legacy bus interfaces. |
| Input Compatibility | TTL-voltage compatible - accepts standard TTL logic levels (0.8 V/2.0 V thresholds), simplifying integration with older logic families. |
| Quiescent Current | 80 µA max - minimizes standby power in battery-backed or low-power 5-V subsystems. |
| 3-State Enable Time | 22 ns typ (ten) at 5.5 V - ensures fast bus release for time-critical arbitration or multiplexing applications. |
| Isolation Leakage | ±5 µA max IOZ - maintains high-impedance integrity during disable, preventing signal contention on shared buses. |
Pinout & Package
SN74HCT645N is housed in a 20-pin plastic dual in-line package (PDIP-N) with 0.3-inch body width and standard through-hole footprint. Pin 1 is located at the top-left corner adjacent to the notch or dot marking.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Determines data flow direction: low = B→A, high = A→B; synchronous with OE for deterministic bus handshaking. |
| 2–9 (A1–A8) | Port A Data I/O | Bidirectional data terminals connected to one bus segment; driven or high-Z depending on DIR/OE state. |
| 10 (GND) | Ground Reference | Primary return path for all internal logic and I/O current; must be low-inductance connection in noise-sensitive systems. |
| 11 (VCC) | Power Supply | +5-V supply input; requires local 0.1-µF ceramic decoupling capacitor placed near pin for stable switching performance. |
| 12–19 (B1–B8) | Port B Data I/O | Bidirectional data terminals connected to second bus segment; electrically isolated from Port A when OE is high. |
| 20 (OE) | Output Enable Input | Active-low control: low enables transceiver, high places both A and B ports in high-impedance state for bus isolation. |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional Bus Interface | Single DIR pin controls full 8-bit data flow direction, eliminating need for separate transmit/receive control logic. |
| High-Current 3-State Outputs | ±6-mA drive supports direct connection to 15 LSTTL loads, enabling robust fanout without external buffers in industrial backplanes. |
| TTL-Compatible Inputs | Accepts standard TTL voltage thresholds (0.8 V/2.0 V), allowing seamless interoperability with legacy 74LS/74ALS logic in mixed-technology systems. |
| Low Power Consumption | 80-µA max ICC enables use in power-constrained 5-V embedded controllers where quiescent current impacts thermal design. |
| Wide Operating Temperature | Rated for −40°C to +85°C ambient, supporting deployment in industrial automation, test equipment, and automotive under-hood ECUs. |
Applications
| Microcontroller Peripheral Expansion | Legacy Memory Bus Interface |
|---|---|
Use Scenario: Expanding GPIO count of an 8-bit MCU (e.g., PIC16F or 8051) to interface with multiple parallel peripherals like LCD modules, keypad scanners, or ADCs. IC Role / Device Role / Timing Role: SN74HCT645N acts as a programmable bidirectional data bridge between MCU port and peripheral bus, with DIR set by software and OE synchronized to address strobes. Use Value: Eliminates need for discrete logic or CPLDs; 14-ns tpd ensures no timing penalty in 1–2 MHz peripheral access cycles. | Use Scenario: Connecting a Z80 or 6502 CPU to external SRAM or EPROM chips sharing a common data/address bus with peripheral I/O devices. IC Role / Device Role / Timing Role: SN74HCT645N isolates memory data bus from I/O bus during read/write cycles using OE gating, while DIR selects direction per memory access phase. Use Value: Prevents bus contention during simultaneous memory and I/O operations; ±6-mA drive sustains signal integrity over 15 cm PCB traces. |
| Industrial Backplane Isolation | Test Equipment Signal Routing |
Use Scenario: Isolating modular sub-systems on a 5-V industrial backplane (e.g., sensor acquisition and actuator driver cards) to prevent ground loops and fault propagation. IC Role / Device Role / Timing Role: SN74HCT645N serves as a hot-swap-capable bus barrier, with OE asserted during card insertion/removal and DIR configured per module data flow direction. Use Value: High-impedance leakage <5 µA ensures minimal crosstalk between powered-down modules; PDIP package allows manual replacement in field service. | Use Scenario: Reconfigurable signal routing in automated test equipment (ATE) where DUT I/O lines must be dynamically connected to different measurement instruments. IC Role / Device Role / Timing Role: SN74HCT645N functions as a software-controlled bidirectional switch matrix element, with DIR and OE coordinated via FPGA or microcontroller to establish signal paths. Use Value: 14-ns tpd supports >30 MHz digital pattern rates; TTL-compatible inputs simplify integration with legacy instrument control logic. |
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 |
|---|---|---|---|
| SN74HCT245N | Same function, identical pinout, but lacks DIR inversion logic - DIR high = A→B, DIR low = B→A (same as SN74HCT645N). | No functional difference in data direction behavior; both support identical bus isolation and drive specs. | Drop-in replacement with identical timing, drive, and compatibility - verified pin-to-pin and functionally equivalent per TI documentation. |
| 74ACT245PC | Higher speed (typical tpd = 8 ns), 5-V only, ±24-mA drive, but higher ICC (40 mA max) and not TTL-input compatible. | Suitable for high-speed 5-V systems requiring faster settling, but incompatible with TTL-level control signals without level translation. | Select when speed >14 ns is required and system uses pure CMOS control logic; avoid if interfacing with legacy TTL drivers. |
Compared with SN74HCT645N, SN74HCT245N offers identical functionality and drop-in compatibility, while 74ACT245PC trades TTL input compatibility and lower power for higher speed and drive - making SN74HCT645N optimal for cost-sensitive, mixed-logic 5-V industrial designs requiring proven reliability and ease of integration.
Availability
SN74HCT645N is available at Aetrix Electronics and suitable for microcontroller peripheral expansion, legacy memory bus interfacing, industrial backplane isolation, and test equipment signal routing requiring stable component supply and long-term obsolescence management.
Supply support for SN74HCT645N 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 specializing in analog, embedded processing, and logic solutions with decades of industrial-grade product heritage.
The SN74HCT645N belongs to TI's 74HCT logic family, engineered for 5-V systems requiring TTL-compatible inputs, low power, and robust noise immunity in industrial and automotive environments.
FAQ
What is the maximum operating temperature range for the SN74HCT645N?
The SN74HCT645N is rated for operation from −40°C to +85°C ambient temperature. This industrial temperature range ensures reliable performance in demanding environments such as factory automation controllers, motor drives, and outdoor instrumentation where thermal cycling and extended uptime are critical. The PDIP package's thermal impedance (69°C/W) supports this rating under typical PCB copper pour conditions.
Can the SN74HCT645N interface directly with 3.3-V logic devices?
No, the SN74HCT645N is not designed for direct 3.3-V logic interfacing. Its inputs require TTL-compatible thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and it operates only from 4.5 V to 5.5 V. Driving its inputs from 3.3-V CMOS outputs may result in marginal or non-functional high-level recognition. For mixed-voltage systems, level-shifting circuitry or a 3.3-V–compatible transceiver like SN74LVC245A is required alongside SN74HCT645N.
How does the DIR pin affect data flow direction in the SN74HCT645N?
In the SN74HCT645N, the DIR pin determines bidirectional data path direction: when DIR is low, data flows from Port B to Port A; when DIR is high, data flows from Port A to Port B. This control is synchronous with the OE signal - data transfer occurs only when OE is low. The logic is non-inverting relative to DIR state, matching standard industry convention for octal transceivers.
What is the purpose of the OE pin on the SN74HCT645N?
The OE (Output Enable) pin on the SN74HCT645N is an active-low control that places both Port A and Port B into high-impedance (3-state) mode when asserted high. This electrically isolates the connected buses, preventing signal contention during bus arbitration, power sequencing, or hot-swap events. When OE is low, the transceiver becomes active and data flows according to the DIR setting.
Is the SN74HCT645N pin-compatible with other 74-series octal transceivers?
Yes, the SN74HCT645N is pin-compatible with SN74HCT245N and SN74LS245N in the PDIP-20 package. All share identical pin assignments for VCC, GND, DIR, OE, and the A/B port terminals. Functional equivalence is confirmed in TI's logic guide - differences exist only in electrical characteristics (e.g., HCT vs LS speed/power), not pinout or basic operation. This enables direct substitution in existing layouts.
SN74HCT645N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HCT
- 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:
- 6mA, 6mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74HCT645N FAQ
1.How can I place an order for SN74HCT645N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74HCT645N 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 SN74HCT645N reliable?
The price and inventory of SN74HCT645N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74HCT645N is usually 5 days.
3.What payment methods are accepted for SN74HCT645N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74HCT645N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74HCT645N?
SN74HCT645N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74HCT645N 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 SN74HCT645N?
For technical support, including SN74HCT645N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74HCT645N requirements.
6.How does Aetrix verify that SN74HCT645N is sourced from the original manufacturer or authorized distributors?
All SN74HCT645N 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 SN74HCT645N meets industry standards.
7.What is the process for return or replacement of SN74HCT645N?
All SN74HCT645N units undergo pre-shipment inspection (PSI). If there is an issue with SN74HCT645N, 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 SN74HCT645N part is unused and in its original packaging.
Return procedure for SN74HCT645N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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