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NXP Semiconductors 74HCT646D,652
- Part No.:
- 74HCT646D,652
- Manufacturer:
- NXP Semiconductors
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
74HCT646D,652.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24SO
- Quantity:
- Payment:
- Shipping:
Inventory:4,063
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Product details
Overview
74HCT646D,652 from Nexperia is an octal bus transceiver/register with 3-state outputs, designed for bidirectional data flow control between two 8-bit buses (A and B). It features independent A/B registers, multiplexed real-time and stored data paths, direction control (DIR), output enable (OE), and dual clock inputs (CPAB/CPBA) for edge-triggered latching. It operates at 4.5 V with typical propagation delay of 13 ns (An/Bn ↔ Bn/An) and supports up to 85 MHz clock frequency - used in microcontroller system bus interfacing and memory-mapped I/O expansion.
For engineers reviewing the 74HCT646D,652 datasheet, 74HCT646D,652 pinout, 74HCT646D,652 application, or 74HCT646D,652 equivalent, key selection criteria include 3-state bus driving capability, register-controlled data storage, direction-selectable real-time vs. registered transfer modes, and TTL-compatible input thresholds at 4.5 V supply.
Technical Context
The 74HCT646D,652 implements a dual-register architecture where A0–A7 and B0–B7 each connect to independent D-type flip-flops clocked by CPAB (A→B) or CPBA (B→A). Its DIR input determines data flow direction during active OE (LOW), while SAB/SBA select between transparent (real-time) or registered (latched) source data per bus path.
It uses Si-gate CMOS technology with TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max at VCC = 4.5 V), 3-state output disable times as low as 44 ns, and supports operation across −40 °C to +125 °C. The device is pin-compatible with LSTTL and compliant with JEDEC standard no. 7A.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74HCT - TTL-compatible input thresholds, CMOS power efficiency, 4.5 V nominal supply |
| Bus Width | Octal (8-bit) bidirectional A and B buses with independent register storage |
| Propagation Delay | 13 ns typical (An/Bn ↔ Bn/An at VCC = 5 V, CL = 15 pF) - enables high-speed bus arbitration |
| Max Clock Frequency | 85 MHz at VCC = 5 V - supports fast synchronous data capture between buses |
| Output Drive | Bus driver capability (±6 mA at VCC = 4.5 V) - directly drives standard CMOS/TTL loads |
| Operating Temperature | −40 °C to +125 °C - qualified for industrial and automotive under-hood applications |
| Input Capacitance | 3.5 pF - minimizes loading on upstream logic and preserves signal integrity |
Pinout & Package
74HCT646D,652 is housed in a 24-pin SO24 (Small Outline) package with 300 mil body width and standard JEDEC MS-013AC outline.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (CPAB) | A-to-B clock input | LOW-to-HIGH edge-triggered latch control for A-bus data into B-register |
| 2 (SAB) | A-to-B source select | Selects real-time (A-bus) or registered (A-register) data for output to B-bus |
| 3 (DIR) | Direction control | Determines active bus direction when OE = LOW: DIR = LOW → A→B; DIR = HIGH → B→A |
| 4–11 (A0–A7) | A-bus I/O terminals | Bidirectional 8-bit data port with 3-state output control and register input path |
| 12 (GND) | Ground reference | 0 V return for all internal logic and output drivers |
| 13–20 (B0–B7) | B-bus I/O terminals | Bidirectional 8-bit data port with 3-state output control and register input path |
| 21 (OE) | Output enable (active LOW) | Disables all bus outputs to high-impedance state; input functions remain active |
| 22 (SBA) | B-to-A source select | Selects real-time (B-bus) or registered (B-register) data for output to A-bus |
| 23 (CPBA) | B-to-A clock input | LOW-to-HIGH edge-triggered latch control for B-bus data into A-register |
| 24 (VCC) | Positive supply voltage | 4.5 V to 5.5 V operation; powers all logic, registers, and output drivers |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B register storage | Enables simultaneous capture and retention of data from both buses without contention |
| Multiplexed real-time and registered data paths | Permits dynamic switching between live bus traffic and previously latched values per direction |
| TTL-compatible input thresholds | Ensures interoperability with legacy 5 V TTL systems without level-shifting circuitry |
| 3-state bus driver outputs | Supports shared bus architectures with multiple drivers via OE-controlled isolation |
| Edge-triggered clock inputs (CPAB/CPBA) | Guarantees deterministic sampling of bus data on rising clock edges, reducing metastability risk |
Applications
| Microcontroller Bus Expansion | Industrial PLC Backplane Interface |
|---|---|
|
Use Scenario: Expanding limited GPIO or address/data bus width of an MCU to interface with external peripherals or memory. IC Role / Device Role / Timing Role: Bidirectional bus transceiver with register buffering to decouple timing between MCU and slower peripherals. Use Value: Enables synchronous handshaking via CPAB/CPBA clocks and eliminates bus contention using DIR/OE control - critical for reliable memory-mapped I/O. |
Use Scenario: Interfacing modular I/O cards to a central PLC CPU backplane with strict noise immunity and thermal stability requirements. IC Role / Device Role / Timing Role: Isolation and direction-controlled data routing between CPU and field modules, with register hold for scan-cycle consistency. Use Value: −40 °C to +125 °C rating and 3-state drive ensure robust operation in harsh cabinet environments; SAB/SBA selection allows deterministic data staging per scan cycle. |
| Legacy System Bus Bridge | Test Equipment Data Acquisition Interface |
|
Use Scenario: Connecting legacy 8-bit ISA-style or Z80-based subsystems to modern controller buses with protocol translation. IC Role / Device Role / Timing Role: Protocol-agnostic bus coupler that buffers and forwards data between asynchronous domains using registered latching. Use Value: Non-inverting data path and pin compatibility with 74LS646 simplify drop-in replacement; DIR and OE allow software-controlled bus arbitration. |
Use Scenario: Capturing parallel sensor or ADC output streams in automated test equipment requiring synchronized sampling and buffering. IC Role / Device Role / Timing Role: High-speed parallel data latch and transient isolation element between acquisition front-end and processing unit. Use Value: 85 MHz max clock and 13 ns propagation delay support sub-12 ns sampling intervals; independent A/B registers enable ping-pong acquisition without CPU intervention. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver/register applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| 74HCT646PW,118 | Same logic function and AC/DC specs; TSSOP24 package (4.4 mm width) vs. SO24 (7.5 mm) | Higher board density required; better thermal dissipation in compact layouts | Select when PCB space is constrained and reflow compatibility with fine-pitch footprints is needed |
| SN74HCT646N | Identical functionality but manufactured by Texas Instruments; wider VCC tolerance (4.5–5.5 V), same timing | No change in system-level behavior; TI's qualification scope differs slightly in automotive AEC-Q100 coverage | Choose for multi-source procurement or TI-aligned BOMs; verify qualification alignment for target application |
Compared with 74HCT646D,652, the 74HCT646PW,118 offers identical electrical performance in a smaller footprint ideal for space-constrained designs, while SN74HCT646N provides second-source assurance with matching timing and drive strength - both require no functional redesign but may need layout adaptation or qualification review.
Availability
74HCT646D,652 is available at Aetrix Electronics and suitable for microcontroller bus expansion, industrial PLC backplane interfaces, legacy system bus bridging, and test equipment data acquisition requiring stable component supply and long-term industrial availability.
Supply support for 74HCT646D,652 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 discrete, logic, and PowerMOS semiconductors, spun off from NXP's Standard Products division in 2017 and focused on automotive, industrial, computing, and consumer markets.
The 74HCT646D,652 belongs to Nexperia's 74HCT logic family - engineered for robust 5 V TTL-compatible operation in industrial control, instrumentation, and legacy system upgrades where reliability and long-term supply are critical.
FAQ
What is the supply voltage range for the 74HCT646D,652?
The 74HCT646D,652 operates over a supply voltage range of 4.5 V to 5.5 V. Its TTL-compatible input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V at VCC = 4.5 V) ensure reliable interfacing with standard 5 V logic families. This range is specified in the "DC Characteristics for 74HCT" section of the Nexperia datasheet and validated across −40 °C to +125 °C ambient temperatures.
Does the 74HCT646D,652 support simultaneous data latching on both A and B buses?
Yes, the 74HCT646D,652 supports independent latching: CPAB triggers A→B register capture, and CPBA triggers B→A register capture. Both clocks are edge-sensitive (LOW-to-HIGH), and their operation is fully decoupled - allowing concurrent storage of data from either bus into its respective register without interference or timing dependency.
How does the DIR input affect data flow in the 74HCT646D,652?
The DIR input determines directionality only when OE is active (LOW). With DIR = LOW, data flows from A bus to B bus; with DIR = HIGH, data flows from B bus to A bus. DIR has no effect on register loading (controlled by CPAB/CPBA) or source selection (SAB/SBA), and does not alter 3-state output behavior when OE = HIGH.
What is the maximum clock frequency supported by the 74HCT646D,652?
The 74HCT646D,652 supports a maximum clock frequency of 85 MHz at VCC = 5 V and Tamb = 25 °C, as confirmed in the Quick Reference Data table. At full industrial temperature range (−40 °C to +125 °C) and VCC = 4.5 V, the guaranteed minimum fmax is 24 MHz per AC characteristics tables - sufficient for most synchronous bus applications.
Can the 74HCT646D,652 be used in place of the 74HC646 variant?
The 74HCT646D,652 can replace 74HC646 in systems requiring TTL-compatible inputs, but not vice versa. While both share identical pinout and logic function, the HCT version accepts VIH ≥ 2.0 V (TTL-level), whereas HC requires VIH ≥ 3.15 V (CMOS-level) at VCC = 4.5 V. Substituting HC for HCT risks input recognition failure in mixed-logic systems.
74HCT646D,652 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- NXP Semiconductors
- Series:
- 74HCT
- Package/Case:
- 24-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tube
- 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,652 FAQ
1.How can I place an order for 74HCT646D,652 through Aetrix?
Please submit a Request for Quotation (RFQ) for 74HCT646D,652 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,652 reliable?
The price and inventory of 74HCT646D,652 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 74HCT646D,652 is usually 5 days.
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74HCT646D,652 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 74HCT646D,652 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,652?
For technical support, including 74HCT646D,652 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 74HCT646D,652 requirements.
6.How does Aetrix verify that 74HCT646D,652 is sourced from the original manufacturer or authorized distributors?
All 74HCT646D,652 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,652 meets industry standards.
7.What is the process for return or replacement of 74HCT646D,652?
All 74HCT646D,652 units undergo pre-shipment inspection (PSI). If there is an issue with 74HCT646D,652, 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,652 part is unused and in its original packaging.
Return procedure for 74HCT646D,652:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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