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NXP Semiconductors 74HCT646N,652
- Part No.:
- 74HCT646N,652
- Manufacturer:
- NXP Semiconductors
- Package:
- 24-DIP (0.600", 15.24mm)
- Datasheet:
-
74HCT646N,652.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24DIP
- Quantity:
- Payment:
- Shipping:
Inventory:2,550
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Product details
Overview
74HCT646N,652 from Nexperia is an octal bus transceiver/register with 3-state outputs, designed for bidirectional data routing and register storage in 5 V TTL-compatible digital systems. It features independent A/B registers, multiplexed real-time/stored data paths, direction control (DIR), output enable (OE), and dual clock inputs (CPAB/CPBA) - enabling synchronized bus isolation and latched transfer in industrial control and computing backplanes.
For engineers reviewing the 74HCT646N,652 datasheet, 74HCT646N,652 pinout, 74HCT646N,652 application, or 74HCT646N,652 equivalent, key selection criteria include 3-state timing (tPZH/tPHZ ≤ 60 ns at VCC = 4.5 V), HCT-level input thresholds (VIH = 2.0 V min), register clock edge sensitivity (LOW-to-HIGH), and dual-bus storage capability under OE HIGH.
Technical Context
The 74HCT646N,652 implements a synchronous octal transceiver architecture with two independent D-type flip-flop registers - one per bus - allowing concurrent capture of A- or B-side data on separate clock edges (CPAB and CPBA). Its DIR input determines data flow direction during active output mode (OE = LOW), while SAB/SBA select between transparent (real-time) and registered (latched) sources.
Unlike standard transceivers, it supports isolation-mode operation (OE = HIGH) where A and B buses remain electrically disconnected yet retain full register access: A data can be clocked into the B register and vice versa. All inputs meet 74HCT TTL-compatible voltage thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V), ensuring interoperability with legacy LSTTL logic without level shifting.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74HCT - TTL-compatible CMOS with 5 V supply and LSTTL input thresholds |
| Propagation Delay (An→Bn) | 16–45 ns typical/max at VCC = 4.5 V, CL = 50 pF - defines maximum system clock rate for real-time transfer |
| Max Clock Frequency | 77 MHz at VCC = 4.5 V - supports high-speed register loading in burst-mode data acquisition |
| 3-State Enable/Disable Time | tPZH/tPHZ ≤ 60 ns, tPHZ/tPLZ ≤ 53 ns - ensures clean bus arbitration in multi-master systems |
| Input Capacitance | CI = 3.5 pF - minimizes capacitive loading on driving gates and preserves signal integrity |
| Power Dissipation Cap. | CPD = 33 pF per channel - enables accurate dynamic power estimation using PD = CPD × VCC² × fi |
Pinout & Package
74HCT646N,652 is supplied in a 24-pin dual in-line package (DIP) with 0.3-inch body width and through-hole mounting. Pin 12 is GND and pin 24 is VCC; all I/O pins are arranged symmetrically across two banks (A0–A7 on pins 4–11, B0–B7 on pins 13–20).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| CPAB (pin 1) | A-to-B register clock input | LOW-to-HIGH edge triggers capture of A-bus data into B-register - enables synchronized write to B side |
| SAB (pin 2) | A-to-B source select | Selects between real-time A data (transparent) or stored A data (registered) for output on B bus |
| DIR (pin 3) | Direction control | When OE = LOW, sets B bus as sink (DIR = LOW) or A bus as sink (DIR = HIGH) - defines physical data path |
| A0–A7 (pins 4–11) | A-bus I/O terminals | Bidirectional 3-state ports - function as inputs when opposite bus drives, outputs when enabled and DIR matches |
| GND (pin 12) | Ground reference | 0 V return for all internal logic and I/O - must be low-impedance for noise immunity |
| B0–B7 (pins 13–20) | B-bus I/O terminals | Identical electrical behavior to A0–A7 - supports symmetrical bus interface design |
| OE (pin 21) | Output enable (active LOW) | Disables all outputs (Hi-Z) when HIGH - isolates both buses without affecting register state |
| SBA (pin 22) | B-to-A source select | Chooses real-time or registered B data for output on A bus - enables flexible read-modify-write cycles |
| CPBA (pin 23) | B-to-A register clock input | LOW-to-HIGH edge captures B-bus data into A-register - allows reverse-direction latching |
| VCC (pin 24) | Positive supply | 5 V ±10 % nominal - powers all logic and output drivers; decoupling required near pin 24 |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent registers | Enables simultaneous capture and retention of A- and B-bus data without cross-contamination - critical for handshake protocols |
| Multiplexed real-time/stored data | SAB/SBA inputs allow runtime switching between live bus signals and previously latched values - supports diagnostic snapshot and replay |
| Isolation-mode register access | Registers remain fully writable even when OE = HIGH and outputs are disabled - permits background data staging |
| TTL-compatible input thresholds | VIH ≥ 2.0 V and VIL ≤ 0.8 V ensure direct interfacing with 5 V LSTTL without external level shifters |
| Bus-driver output capability | Outputs drive standard 50 Ω transmission lines or 10 LSTTL loads - eliminates need for external buffers in medium-density backplanes |
Applications
| Industrial PLC Backplane Interface | Legacy System Bus Extender |
|---|---|
Use Scenario: Connecting isolated I/O modules to a central controller via shared 8-bit data bus with strict timing and fault containment requirements. IC Role / Device Role / Timing Role: Bidirectional bus transceiver with register staging - buffers and synchronizes data between asynchronous modules while preventing bus contention. Use Value: DIR and OE control enable deterministic bus arbitration; CPAB/CPBA clocks allow precise timestamping of sensor readings before forwarding to CPU. |
Use Scenario: Extending a vintage microprocessor bus (e.g., Z80 or 8085) to support additional memory-mapped peripherals without modifying existing address/data routing. IC Role / Device Role / Timing Role: Registered bus repeater - captures and holds address/data during wait states, then forwards with controlled timing to downstream devices. Use Value: SAB/SBA multiplexing allows seamless switching between live CPU bus traffic and pre-loaded configuration data - simplifies firmware-upgrade sequences. |
| Test Equipment Data Capture Module | Automotive ECU Diagnostic Interface |
Use Scenario: Capturing parallel sensor outputs (e.g., ADC result buses) at precise intervals and holding them for serial upload to host PC. IC Role / Device Role / Timing Role: Dual-register data latch - samples parallel inputs on CPAB edge, stores in A register, then transfers to B register for UART interface timing alignment. Use Value: Independent CPAB/CPBA clocks permit staggered sampling and zero-latency handoff - eliminates pipeline stalls during high-frequency capture. |
Use Scenario: Interfacing a modern CAN controller's parallel debug port to an older diagnostic tool with 8-bit ISA-style bus interface. IC Role / Device Role / Timing Role: Protocol-agnostic bus translator - isolates CAN controller from tool-side noise while buffering status/control words. Use Value: OE-controlled Hi-Z isolation prevents backfeeding during tool reset; DIR toggling enables bidirectional command/response exchange without external logic. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal registered transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| 74HCT640N,652 | Inverting data path; no register storage - only 3-state transceiver functionality | Lacks clocked register capability; suitable only for simple bus isolation without latching | Choose when real-time bidirectional pass-through is sufficient and register staging is unnecessary |
| SN74HCT245N | No internal registers; single DIR pin; no SAB/SBA multiplexing - basic 8-bit non-inverting transceiver | Supports only transparent data flow; cannot store or time-align data from either bus | Select for cost-sensitive designs requiring only bus buffering without timing control or data staging |
Compared with 74HCT646N,652, the 74HCT640N,652 omits register functionality entirely, while SN74HCT245N provides no clocking or source selection - making both unsuitable for applications requiring synchronized latched transfer or multiplexed real-time/stored data routing.
Availability
74HCT646N,652 is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy system bus extension, test equipment data capture modules, and automotive ECU diagnostic interfaces requiring stable component supply and long-term obsolescence management.
Supply support for 74HCT646N,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, formed in 2017 from the former NXP Standard Products division.
The 74HCT646N,652 belongs to Nexperia's 74HCT logic family, engineered for robust 5 V TTL-compatible operation in automotive, industrial, and computing applications where reliability and pin compatibility with legacy LSTTL are essential.
FAQ
What is the supply voltage range for the 74HCT646N,652?
The 74HCT646N,652 operates over a supply voltage range of 4.5 V to 5.5 V, with guaranteed performance at VCC = 4.5 V (as specified in AC characteristics tables). Operation outside this range may cause undefined logic states or excessive ICC, and is not supported per Nexperia's datasheet. The device is not rated for 3.3 V operation - use 74LVC646 for lower-voltage systems.
Does the 74HCT646N,652 support simultaneous registration of A and B bus data?
Yes, the 74HCT646N,652 supports independent registration: A-bus data is latched into the B-register on the LOW-to-HIGH transition of CPAB, and B-bus data is latched into the A-register on the LOW-to-HIGH transition of CPBA. These clocks operate asynchronously, enabling true concurrent capture without shared timing constraints - confirmed in the functional diagram and timing waveforms.
How does the 74HCT646N,652 behave when OE is HIGH?
When OE is HIGH, all A0–A7 and B0–B7 outputs enter high-impedance (Hi-Z) state, electrically isolating both buses. Critically, input functions remain fully active: CPAB, CPBA, SAB, SBA, DIR, and bus inputs continue to operate normally - allowing registers to be loaded and source selection updated without affecting bus integrity.
Is the 74HCT646N,652 pin-compatible with the 74HC646N?
Yes, the 74HCT646N,652 is pin-compatible with the 74HC646N - same 24-pin DIP footprint, identical pin numbering, and matching functional assignments. However, the HCT version uses TTL-compatible input thresholds (VIH ≥ 2.0 V), whereas HC requires CMOS thresholds (VIH ≥ 3.5 V at VCC = 5 V), making HCT the correct choice for mixed LSTTL/CMOS systems.
What is the maximum data rate supported by the 74HCT646N,652 in real-time (transparent) mode?
In transparent mode (SAB = L or H depending on DIR, OE = LOW), the 74HCT646N,652 supports real-time data transfer with propagation delay tPHL/tPLH ≤ 45 ns (max at VCC = 4.5 V, CL = 50 pF). This corresponds to a theoretical maximum toggle rate of ~11 MHz for reliable edge-aligned signaling - verified in the AC characteristics table under "An,Bn to Bn,An" delay.
74HCT646N,652 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- NXP Semiconductors
- Series:
- 74HCT
- Package/Case:
- 24-DIP (0.600", 15.24mm)
- 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:
- Through Hole
- Supplier Device Package:
- 24-DIP
74HCT646N,652 FAQ
1.How can I place an order for 74HCT646N,652 through Aetrix?
Please submit a Request for Quotation (RFQ) for 74HCT646N,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 74HCT646N,652 reliable?
The price and inventory of 74HCT646N,652 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 74HCT646N,652 is usually 5 days.
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74HCT646N,652 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 74HCT646N,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 74HCT646N,652?
For technical support, including 74HCT646N,652 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 74HCT646N,652 requirements.
6.How does Aetrix verify that 74HCT646N,652 is sourced from the original manufacturer or authorized distributors?
All 74HCT646N,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 74HCT646N,652 meets industry standards.
7.What is the process for return or replacement of 74HCT646N,652?
All 74HCT646N,652 units undergo pre-shipment inspection (PSI). If there is an issue with 74HCT646N,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 74HCT646N,652 part is unused and in its original packaging.
Return procedure for 74HCT646N,652:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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