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NXP Semiconductors 74HCT646D,653
- Part No.:
- 74HCT646D,653
- Manufacturer:
- NXP Semiconductors
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
74HCT646D,653.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24SO
- Quantity:
- Payment:
- Shipping:
Inventory:4,799
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Product details
Overview
74HCT646D,653 from Nexperia is an octal bus transceiver/register with 3-state outputs, designed for bidirectional data flow control between two 8-bit buses. It features independent A/B registers, real-time and stored data multiplexing, direction-controlled transceivers, and operates at 4.5 V with typical propagation delay of 16 ns (A/B to B/A) and max clock frequency of 77 MHz. It is used in microprocessor system data bus isolation and register staging.
For engineers reviewing the 74HCT646D,653 datasheet, 74HCT646D,653 pinout, 74HCT646D,653 application, or 74HCT646D,653 equivalent, key selection criteria include 3-state bus driver capability, dual-clock edge-triggered register storage (CPAB/CPBA), DIR/OE-controlled direction and output enable, and HCT-level TTL-compatible input thresholds.
Technical Context
The 74HCT646D,653 implements a dual-register transceiver architecture: each bus (A0–A7 and B0–B7) connects to dedicated D-type flip-flops clocked by CPAB (A→B) or CPBA (B→A), enabling synchronous data capture. Select inputs SAB/SBA allow multiplexing between transparent (real-time) and registered data paths.
Direction (DIR) determines bus ownership during active output (OE = LOW); when OE = HIGH, both buses enter high-impedance isolation while internal registers remain writable. Input functions stay enabled regardless of OE state, supporting concurrent storage and transmission.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | HCT - TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max at VCC = 4.5 V) |
| Supply Voltage | 4.5 V to 5.5 V - ensures interoperability with 5 V TTL and mixed-voltage system backplanes |
| Propagation Delay | 16 ns typ. (An/Bn → Bn/An at VCC = 4.5 V, CL = 50 pF) - enables ≤77 MHz clock operation in synchronous bus systems |
| Output Drive | ±6 mA at VCC = 4.5 V - meets standard bus driver requirements for driving 10 LSTTL loads |
| Input Capacitance | 3.5 pF - minimizes capacitive loading on upstream logic and supports high-speed signal integrity |
| Power Dissipation Cap. | 33 pF per channel - used to calculate dynamic power: PD = CPD × VCC² × fi + Σ(CL × VCC² × fo) |
| Operating Temperature | −40 °C to +125 °C - qualified for industrial and automotive under-hood applications |
Pinout & Package
74HCT646D,653 is housed in a 24-pin SO24 (Small Outline) package per JEDEC MS-013AC, 300 mil body width, with 1.27 mm pitch and gull-wing leads.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (CPAB) | A-to-B clock input | LOW-to-HIGH edge-triggered; latches A-bus data into B-register for stored-path transfer |
| 2 (SAB) | A-to-B source select | Chooses between real-time A data (SAB = LOW) or registered A data (SAB = HIGH) on B-bus output |
| 3 (DIR) | Direction control | When OE = LOW: DIR = LOW drives A→B; DIR = HIGH drives B→A |
| 4–11 (A0–A7) | A-bus I/O | Bidirectional 8-bit port; inputs when A-bus is driven by external source, outputs when DIR/OE enable A-drive |
| 12 (GND) | Ground reference | 0 V return path for all internal logic and I/O circuits |
| 13–20 (B0–B7) | B-bus I/O | Bidirectional 8-bit port; functions symmetrically to A0–A7 under DIR-controlled direction |
| 21 (OE) | Output enable | Active LOW: enables transceiver outputs; HIGH places all A/B pins in high-impedance state |
| 22 (SBA) | B-to-A source select | Chooses between real-time B data (SBA = LOW) or registered B data (SBA = HIGH) on A-bus output |
| 23 (CPBA) | B-to-A clock input | LOW-to-HIGH edge-triggered; latches B-bus data into A-register for stored-path transfer |
| 24 (VCC) | Positive supply | 4.5–5.5 V power rail for CMOS core and output buffers |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent registers | Separate A→B and B→A D-flip-flop banks allow simultaneous storage of data from both buses without interference |
| Multiplexed real-time & stored data | SAB/SBA inputs select between live bus signals or previously clocked register contents - enables flexible data routing in one cycle |
| Asymmetric 3-state control | OE disables all outputs; DIR selects direction *only* when OE is active - prevents bus contention during mode transitions |
| TTL-compatible inputs | HCT family ensures direct interfacing with legacy 5 V TTL without level shifters, reducing BOM count and layout complexity |
| Bus-driver output strength | ±6 mA drive at VCC = 4.5 V meets 10-LSTTL load requirement - supports fan-out to multiple downstream devices on shared bus |
Applications
| Microprocessor Data Bus Interface | Memory-Mapped I/O Expansion |
|---|---|
Use Scenario: Isolating CPU address/data bus from peripheral subsystems during DMA or multi-master arbitration. IC Role / Device Role / Timing Role: Bidirectional 3-state transceiver with register staging to decouple timing domains and prevent bus contention. Use Value: Enables CPU to read/write peripheral registers while simultaneously storing next-cycle data in A/B registers - improves throughput in burst-mode transfers. |
Use Scenario: Adding parallel I/O ports or configuration registers to an 8-bit microcontroller system with limited GPIO. IC Role / Device Role / Timing Role: Octal register-transceiver providing synchronized, direction-controlled interface between MCU data bus and external latch-based peripherals. Use Value: Allows single-cycle access to peripheral status/control registers while buffering data for subsequent writes - eliminates software wait states. |
| Industrial PLC Backplane Staging | Legacy System Bus Bridge |
Use Scenario: Interfacing modular I/O cards to a central controller over a shared 8-bit parallel backplane with noise and timing skew. IC Role / Device Role / Timing Role: Registered transceiver providing deterministic setup/hold timing (tsu = 12 ns, th = 5 ns at VCC = 4.5 V) and ESD-tolerant I/O. Use Value: Eliminates metastability risk in noisy industrial environments by synchronizing asynchronous module data into local registers before bus transfer. |
Use Scenario: Connecting modern FPGA-based controllers to legacy 8-bit ISA or VMEbus peripherals requiring TTL-level signaling and strict timing. IC Role / Device Role / Timing Role: Level-shifting, direction-managed bus interface with HCT input compatibility and 3-state isolation for hot-swap-safe operation. Use Value: Maintains full electrical and timing compliance with 1980s–1990s bus standards while enabling drop-in replacement of obsolete 74LS646 parts. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal registered transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| 74HCT646PW,118 | TSSOP24 package (4.4 mm width); identical logic, AC/DC specs, and pinout | Higher board density; requires finer-pitch reflow profile; not suitable for through-hole prototyping | Select for space-constrained PCBs where thermal performance and footprint size outweigh hand-soldering needs |
| SN74HCT646N | PDIP24 package; same electrical specs but higher parasitic inductance/capacitance; slower edge rates | Through-hole assembly; preferred for lab validation, educational kits, and low-volume industrial controls | Choose for ease of manual soldering, socket-based testing, or legacy DIP-based system upgrades |
Compared with 74HCT646D,653, the TSSOP variant offers superior thermal dissipation and smaller footprint for high-density designs, while the PDIP version provides mechanical robustness and compatibility with breadboard and socket-based development - all three share identical functional behavior and timing.
Availability
74HCT646D,653 is available at Aetrix Electronics and suitable for microprocessor bus interfaces, memory-mapped I/O expansion, and industrial PLC backplane staging requiring stable component supply across long-lifecycle embedded programs.
Supply support for 74HCT646D,653 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
Nexperia is a global leader in high-volume production of discrete, logic, and PowerMOS semiconductors, spun off from NXP's Standard Products division in 2017 and focused on automotive, industrial, and computing applications.
The 74HCT646D,653 belongs to Nexperia's 74HCT logic family - engineered for robust 5 V TTL-compatible operation in noise-prone industrial control and legacy system upgrade applications.
FAQ
What is the maximum operating frequency of the 74HCT646D,653?
The 74HCT646D,653 supports a maximum clock frequency of 77 MHz at VCC = 4.5 V and Tamb = +25 °C, as specified in the AC characteristics table. This value decreases to 24 MHz at −40 °C to +125 °C over temperature, ensuring reliable operation in extended industrial environments where the 74HCT646D,653 is commonly deployed.
Does the 74HCT646D,653 support live data pass-through without registration?
Yes, the 74HCT646D,653 supports real-time (transparent) data transfer via its SAB and SBA select inputs. When SAB = LOW, A-bus data appears directly on the B-bus output; when SBA = LOW, B-bus data passes through to the A-bus - all while maintaining full 3-state control via OE and direction control via DIR.
Can both A and B buses be driven simultaneously by the 74HCT646D,653?
No. The 74HCT646D,653 enforces strict bus isolation: only one bus (A or B) may be actively driven at any time. This is enforced by the DIR input - when OE = LOW, DIR = LOW enables A→B drive, and DIR = HIGH enables B→A drive. Simultaneous drive is electrically prohibited to prevent bus contention and damage.
What is the input voltage threshold compatibility of the 74HCT646D,653?
The 74HCT646D,653 uses TTL-compatible input thresholds: VIH = 2.0 V (min) and VIL = 0.8 V (max) at VCC = 4.5 V. This allows direct connection to standard 5 V TTL outputs without level shifting, making the 74HCT646D,653 ideal for interfacing with legacy LSTTL, ALS, and AS logic families in mixed-technology systems.
How does the 74HCT646D,653 handle power supply decoupling?
The 74HCT646D,653 requires a 100 nF ceramic capacitor placed as close as possible to the VCC (pin 24) and GND (pin 12) pins to suppress switching noise and maintain stable core voltage during output transitions. This decoupling is critical to meet the specified 16 ns propagation delay and prevent ground bounce that could corrupt register clocking in the 74HCT646D,653.
74HCT646D,653 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- NXP Semiconductors
- Series:
- 74HCT
- Package/Case:
- 24-SOIC (0.295", 7.50mm 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 ~ 125°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-SO
74HCT646D,653 FAQ
1.How can I place an order for 74HCT646D,653 through Aetrix?
Please submit a Request for Quotation (RFQ) for 74HCT646D,653 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 74HCT646D,653 reliable?
The price and inventory of 74HCT646D,653 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 74HCT646D,653 is usually 5 days.
3.What payment methods are accepted for 74HCT646D,653?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 74HCT646D,653 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for 74HCT646D,653?
74HCT646D,653 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 74HCT646D,653 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 74HCT646D,653?
For technical support, including 74HCT646D,653 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 74HCT646D,653 requirements.
6.How does Aetrix verify that 74HCT646D,653 is sourced from the original manufacturer or authorized distributors?
All 74HCT646D,653 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 74HCT646D,653 meets industry standards.
7.What is the process for return or replacement of 74HCT646D,653?
All 74HCT646D,653 units undergo pre-shipment inspection (PSI). If there is an issue with 74HCT646D,653, 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 74HCT646D,653 part is unused and in its original packaging.
Return procedure for 74HCT646D,653:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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