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Texas Instruments SN74HCT645PWRE4
- Part No.:
- SN74HCT645PWRE4
- Manufacturer:
- Texas Instruments
- Package:
- 20-TSSOP (0.173", 4.40mm Width)
- Datasheet:
-
SN74HCT645PWRE4.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:4,876
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Product details
Overview
SN74HCT645PWRE4 from Texas Instruments is an octal bus transceiver IC designed for asynchronous two-way data communication between A and B buses in 5-V digital systems. It features direction control (DIR), output-enable (OE), ±6-mA drive strength at 5 V, 14-ns typical propagation delay, and TTL-compatible inputs. It is used in bidirectional data buffering for microcontroller peripheral interfaces and legacy parallel bus systems.
For engineers reviewing the SN74HCT645PWRE4 datasheet, SN74HCT645PWRE4 pinout, SN74HCT645PWRE4 application, or SN74HCT645PWRE4 equivalent, key selection criteria include bidirectional bus isolation timing, 3-state output leakage (≤5 µA), thermal resistance (83°C/W), and TSSOP-20 package compatibility with high-density PCB layouts.
Technical Context
This device implements true logic-level translation with no internal inversion: data flows A→B when DIR = HIGH and B→A when DIR = LOW. The 3-state outputs are fully disabled under OE = HIGH, achieving high-impedance isolation with ≤5 µA off-state current.
It operates strictly within 4.5 V to 5.5 V supply range and supports LSTTL load driving (up to 15 loads). Input thresholds are fixed at VIH = 2.0 V min and VIL = 0.8 V max, ensuring robust noise margin against TTL-family signals.
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 stable operation across industrial voltage tolerances. |
| Propagation Delay | 14 ns typ at 5.5 V - enables reliable timing in 35-MHz+ bus cycles with margin for setup/hold in synchronous transfers. |
| Output Drive | ±6 mA at 5 V - sufficient to directly drive 15 LSTTL inputs without external buffers in legacy parallel interfaces. |
| Input Current | ±1 µA max - minimizes loading on upstream drivers and preserves fanout integrity in large bus networks. |
| Off-State Leakage | ±5 µA max - guarantees effective bus isolation during OE assertion, preventing signal contention in shared-bus architectures. |
| Power Consumption | 80 µA max ICC - supports low-static-power system design where standby current impacts overall board-level efficiency. |
| Logic Compatibility | TTL-voltage inputs - eliminates need for level-shifting circuitry when interfacing with 74LS, 74F, or other TTL-family controllers. |
Pinout & Package
TSSOP-20 package (PW), 6.5 mm × 4.4 mm footprint, 1.2 mm max height, lead pitch 0.65 mm, RoHS-compliant NiPdAu finish, MSL Level-1.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | High = A-to-B data flow; Low = B-to-A - determines real-time bus traffic direction without clock or state machine. |
| 2–9 (A1–A8) | Bus A Data Terminals | Bi-directional I/O pins connected to primary data bus; high-impedance when OE = High or DIR mismatch. |
| 10 (GND) | Ground Reference | System return path for all internal logic and output drivers; must be low-inductance connection for noise immunity. |
| 11 (VCC) | Power Supply | +5 V supply rail; requires local 0.1-µF ceramic decoupling adjacent to pin for transient current stability. |
| 12 (OE) | Output Enable Input | Low = active transceiver; High = 3-state isolation - enables dynamic bus arbitration and hot-swap-safe disconnection. |
| 13–20 (B1–B8) | Bus B Data Terminals | Bi-directional I/O pins connected to secondary data bus; electrically identical to A-side terminals. |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional Bus Control | Single DIR pin configures full-duplex data path direction in real time - eliminates need for separate transmit/receive ICs or complex glue logic. |
| True 3-State Outputs | OE-controlled high-impedance state with <5 µA leakage - ensures zero DC coupling between isolated buses, critical for multi-master arbitration. |
| TTL-Compatible Inputs | VIH = 2.0 V min / VIL = 0.8 V max - allows direct connection to 74LS, 74F, and older microcontrollers without level shifters or pull-up resistors. |
| Low Static Power | 80 µA max ICC - reduces quiescent power in always-on subsystems such as industrial I/O modules and diagnostic ports. |
| High-Noise Immunity | Input hysteresis not specified, but guaranteed 0.4 V noise margin at 5 V - supports reliable operation in electrically noisy factory-floor environments. |
Applications
| Microcontroller Parallel Interface | Legacy Peripheral Expansion |
|---|---|
Use Scenario: Connecting an 8-bit microcontroller's data bus to external SRAM or LCD controller via shared address/data lines. IC Role / Device Role / Timing Role: SN74HCT645PWRE4 acts as a bidirectional data buffer, isolating MCU pins from bus capacitance while enabling read/write direction switching via DIR. Use Value: Eliminates timing skew between address and data lines by providing matched 14-ns propagation delay and ±6-mA drive for clean signal edges. | Use Scenario: Extending ISA or PC/104 bus segments in industrial PCs to add custom I/O cards without signal degradation. IC Role / Device Role / Timing Role: SN74HCT645PWRE4 serves as a bus repeater, regenerating TTL-level signals across backplane traces exceeding 15 cm. Use Value: Supports up to 15 LSTTL loads per line, maintaining signal integrity across long traces where capacitive loading would otherwise cause rise/fall time degradation. |
| Multi-Master Bus Arbitration | Test Equipment Signal Routing |
Use Scenario: Enabling two microcontrollers to share a common memory-mapped peripheral bus with dynamic master handoff. IC Role / Device Role / Timing Role: SN74HCT645PWRE4 provides hardware-enforced bus isolation via OE, preventing contention when one controller releases the bus. Use Value: Sub-50 ns enable/disable times (ten/tdis) allow rapid bus ownership transfer with minimal dead time between masters. | Use Scenario: Configurable signal routing in automated test equipment (ATE) where DUT interface lines must be dynamically connected to measurement or stimulus channels. IC Role / Device Role / Timing Role: SN74HCT645PWRE4 functions as a programmable signal switch, using DIR/OE to route bidirectional data paths under FPGA control. Use Value: TSSOP-20 package enables dense layout in compact ATE modules, while 83°C/W θJA supports convection-cooled chassis designs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74HCT245PW | Same logic function, identical pinout, but lacks DIR pin - uses separate A→B and B→A control signals (A/B select). | Requires additional GPIO or decoder logic to manage direction; less efficient for simple bidirectional links. | Choose SN74HCT245PW only if existing firmware already implements dual-control signaling or board layout reserves space for extra trace routing. |
| 74LCX245MTCX | Lower VCC range (2.0–3.6 V), higher speed (tPD = 5.5 ns), but incompatible with 5-V TTL inputs - requires level shifting. | Not suitable for direct replacement in 5-V systems; intended for mixed-voltage 3.3-V core + 5-V peripheral designs. | Select 74LCX245MTCX only when migrating to 3.3-V logic domains and adding dedicated level translators for upstream TTL sources. |
Compared with SN74HCT245PW and 74LCX245MTCX, the SN74HCT645PWRE4 uniquely integrates single-pin direction control and native 5-V TTL compatibility in a space-efficient TSSOP-20 package - making it optimal for retrofitting legacy 5-V systems requiring minimal firmware or layout changes.
Availability
SN74HCT645PWRE4 is available at Aetrix Electronics and suitable for industrial control panels, test instrumentation, and embedded computing platforms requiring stable component supply and long-term obsolescence management.
Supply support for SN74HCT645PWRE4 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 over 50 years of innovation in industrial, automotive, and communications markets.
The SN74HCT645PWRE4 belongs to TI's HCT logic family, engineered for seamless 5-V TTL-to-CMOS interfacing in cost-sensitive, noise-resilient industrial control and legacy system upgrades.
FAQ
What is the maximum operating temperature range for the SN74HCT645PWRE4?
The SN74HCT645PWRE4 is rated for operation from −40°C to +85°C ambient temperature. This industrial-grade range ensures reliable performance in factory automation, outdoor kiosks, and power supply monitoring systems where thermal cycling and extended uptime are critical. The TSSOP-20 package's 83°C/W junction-to-ambient thermal resistance supports this rating under typical PCB copper pour conditions.
Does the SN74HCT645PWRE4 require external pull-up or pull-down resistors on DIR or OE pins?
No, the SN74HCT645PWRE4 does not require external biasing on DIR or OE. Its CMOS input structure draws ≤1 µA, and internal design ensures valid logic levels at VIH ≥ 2.0 V and VIL ≤ 0.8 V. However, TI recommends tying unused inputs to VCC or GND per SCBA004 to prevent floating nodes that could increase ICC or cause erratic behavior - a best practice applied to all SN74HCT645PWRE4 implementations.
Can the SN74HCT645PWRE4 drive a 50-pF load with guaranteed timing?
Yes, the SN74HCT645PWRE4 guarantees tPD = 14 ns (typical) and tPD ≤ 25 ns (max) at VCC = 5.5 V into a 50-pF load, as specified in the switching characteristics table. This meets timing requirements for 25-MHz bus clocks with 20-ns period margins. For 150-pF loads, tPD increases to ≤34 ns - still viable for lower-speed legacy peripherals like parallel EEPROMs or character LCDs.
Is the SN74HCT645PWRE4 pin-compatible with other TSSOP-20 octal transceivers?
The SN74HCT645PWRE4 shares the same TSSOP-20 mechanical footprint and pinout as SN74HCT245PW and SN74AHCT645PW, but functional pin mapping differs: DIR replaces the B-enable signal found on SN74HCT245PW. Therefore, while solder-compatible, direct substitution requires firmware and schematic validation - especially for DIR-driven direction control versus dual-enable schemes.
What is the recommended PCB layout practice for minimizing noise on the SN74HCT645PWRE4 power pins?
Place a 0.1-µF X7R ceramic capacitor between VCC (pin 11) and GND (pin 10) as close as possible to the SN74HCT645PWRE4 body - ideally within 2 mm trace length. Use solid ground plane beneath the IC and avoid routing high-speed signals under the package. The TSSOP-20's exposed pad is not electrically connected; no thermal pad grounding is required, but ensure solder mask clearance matches TI's land pattern recommendations to prevent bridging.
SN74HCT645PWRE4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HCT
- Package/Case:
- 20-TSSOP (0.173", 4.40mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- 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:
- Surface Mount
- Supplier Device Package:
- 20-TSSOP
SN74HCT645PWRE4 FAQ
1.How can I place an order for SN74HCT645PWRE4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74HCT645PWRE4 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 SN74HCT645PWRE4 reliable?
The price and inventory of SN74HCT645PWRE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74HCT645PWRE4 is usually 5 days.
3.What payment methods are accepted for SN74HCT645PWRE4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74HCT645PWRE4 transactions.
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4.How is shipping managed for SN74HCT645PWRE4?
SN74HCT645PWRE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74HCT645PWRE4 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 SN74HCT645PWRE4?
For technical support, including SN74HCT645PWRE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74HCT645PWRE4 requirements.
6.How does Aetrix verify that SN74HCT645PWRE4 is sourced from the original manufacturer or authorized distributors?
All SN74HCT645PWRE4 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 SN74HCT645PWRE4 meets industry standards.
7.What is the process for return or replacement of SN74HCT645PWRE4?
All SN74HCT645PWRE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74HCT645PWRE4, 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 SN74HCT645PWRE4 part is unused and in its original packaging.
Return procedure for SN74HCT645PWRE4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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