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Texas Instruments CD74HC646EN
- Part No.:
- CD74HC646EN
- Manufacturer:
- Texas Instruments
- Package:
- 24-DIP (0.300", 7.62mm)
- Datasheet:
-
CD74HC646EN.pdf
- Description:
- IC TXRX NON-INVERT 6V 24DIP
- Quantity:
- Payment:
- Shipping:
Inventory:989
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Product details
Overview
CD74HC646EN from Texas Instruments is an octal bus transceiver/register with three-state non-inverting outputs, featuring independent D-type flip-flop registers for A and B buses, 12ns typical propagation delay (A↔B) at 5V/15pF, and operation across -55°C to +125°C. It enables bidirectional data routing in high-reliability industrial backplanes and legacy microprocessor bus interfaces.
For engineers reviewing the CD74HC646EN datasheet, CD74HC646EN pinout, CD74HC646EN application, or CD74HC646EN equivalent, key selection criteria include its dual-register storage capability, direction-controlled real-time vs. registered data routing, three-state bus isolation timing, and compatibility with 2V–6V HC logic families.
Technical Context
The CD74HC646EN implements edge-triggered D-type flip-flops on both A and B buses, clocked independently by CAB and CBA inputs on low-to-high transitions. Its DIR input selects data flow direction while OE enables/disables outputs, and SAB/SBA select between transparent or registered data sources per bus.
It supports simultaneous storage of A and B bus data in separate registers during high-impedance output mode, with no gating of clocks by DIR or OE - enabling asynchronous register loading regardless of transceiver state. Propagation delays are balanced (tPLH ≈ tPHL), and transition times remain consistent across voltage (2V–6V) and temperature (-55°C to 125°C).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | High-speed CMOS (HC), compatible with 2V–6V supply |
| Bus Width | Octal (8-bit) bidirectional transceiver with dual internal registers |
| Propagation Delay | 12ns typical (A→B or B→A) at VCC = 5V, CL = 15pF, 25°C |
| Operating Temperature | -55°C to +125°C - suitable for extended industrial and aerospace environments |
| Output Drive | 15 LSTTL loads - sufficient for legacy TTL bus loading without buffers |
| Three-State Leakage | ±5µA max at -55°C to +125°C - ensures stable high-Z bus holdover |
| Input Noise Immunity | NIL/NIL = 30% of VCC at 5V - robust against EMI in noisy systems |
Pinout & Package
CD74HC646EN uses a 24-pin plastic dual in-line package (PDIP) with 0.3-inch body width and standard through-hole mounting. Pin numbering follows JEDEC MS-001, with GND at Pin 12 and VCC at Pin 24.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (CAB) | A-Bus Clock Input | Low-to-high edge clocks A-bus data into internal D-flip-flop register |
| 2 (SAB) | A-Bus Source Select | Selects whether A-output drives real-time or registered B-bus data |
| 3 (DIR) | Direction Control | Low = B→A data flow; High = A→B data flow |
| 4–11 (A0–A7) | A-Bus I/O Terminals | Bidirectional data lines; high-impedance when OE = High |
| 12 (GND) | Ground Reference | Primary power return path for logic and I/O circuitry |
| 13–14, 16–19, 21–23 (B0–B7) | B-Bus I/O Terminals | Bidirectional data lines; pin order matches functional grouping (B0–B7 contiguous) |
| 15 (SBA) | B-Bus Source Select | Selects whether B-output drives real-time or registered A-bus data |
| 20 (OE) | Output Enable | Low = outputs active; High = all I/Os enter high-impedance state |
| 22 (CBA) | B-Bus Clock Input | Low-to-high edge clocks B-bus data into internal D-flip-flop register |
| 24 (VCC) | Positive Supply | 2V–6V DC supply; decoupling required within 10mm of pin |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B Registers | Enables concurrent capture and retention of data from both buses - critical for handshake protocols and bus arbitration |
| Non-Inverting Three-State Outputs | Preserves signal polarity while allowing multiple devices to share a common bus without contention |
| Real-Time + Registered Data Multiplexing | SAB/SBA inputs let system choose live or latched data per bus - supports mixed synchronous/asynchronous subsystems |
| Wide Voltage Operation (2V–6V) | Interoperates with 3.3V microcontrollers and 5V legacy peripherals without level shifters |
| High Noise Immunity (30% VCC) | Reduces false triggering in electrically noisy industrial enclosures and motor drive cabinets |
Applications
| Industrial Backplane Interface | Legacy Microprocessor Bus Extension |
|---|---|
Use Scenario: Interfacing a modern FPGA-based controller to a legacy 8-bit ISA-style backplane with parallel address/data buses. IC Role / Device Role / Timing Role: Bidirectional bus transceiver with register staging to synchronize FPGA clock domain with asynchronous backplane timing. Use Value: Enables deterministic data capture via CAB/CBA clocks while isolating buses during arbitration using OE and DIR control. |
Use Scenario: Extending Z80 or 8085 CPU address/data bus to additional peripheral cards in a modular test instrument rack. IC Role / Device Role / Timing Role: Octal transceiver providing direction-controlled data flow and latch storage for handshaking with slow peripherals. Use Value: Supports both real-time and registered transfer modes - critical for meeting setup/hold timing with variable peripheral response latency. |
| Military Avionics Data Mux | Automated Test Equipment (ATE) Channel Isolation |
Use Scenario: Routing sensor data between redundant flight computers in a MIL-STD-1553B auxiliary interface module. IC Role / Device Role / Timing Role: High-reliability bus register managing time-stamped telemetry packets across dual-redundant data paths. Use Value: -55°C to +125°C rating and independent register storage ensure deterministic packet buffering during thermal cycling and fault switchover. |
Use Scenario: Isolating DUT (device under test) signals from shared ATE resource buses during parametric testing sequences. IC Role / Device Role / Timing Role: Three-state bus driver enabling precise channel enable/disable sequencing without signal contention. Use Value: 15 LSTTL load drive and fast 12ns propagation support high-speed digital pattern generation with minimal skew across 8-bit channels. |
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 |
|---|---|---|---|
| SN74HC646N | Same logic function and pinout; TI's current-generation HC variant with updated process and tighter AC specs | Higher fMAX (35MHz vs. 30MHz at 6V), lower ICC (8µA vs. 160µA max), RoHS-compliant | Preferred for new designs requiring lifecycle assurance and improved power efficiency |
| CD74HCT646E | TTL-compatible input thresholds (VIH = 2V min); identical pinout and register architecture | Designed for mixed 5V TTL/CMOS systems where input noise margins differ from pure HC levels | Use only when interfacing directly to 74LS-series logic without level translation |
Compared with CD74HC646EN, SN74HC646N offers superior long-term availability and lower static power, while CD74HCT646E provides guaranteed TTL-level input compatibility - neither is pin-compatible with CD74HC646EN due to differing package types (SOIC vs. PDIP) and obsolescence status.
Availability
CD74HC646EN is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy microprocessor bus extensions, military avionics data muxing, and automated test equipment channel isolation requiring stable component supply despite its obsolete status.
Supply support for CD74HC646EN 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 founded in 1930, delivering analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The CD74HC646EN belongs to TI's legacy HC logic family, designed specifically for high-noise, wide-temperature industrial and defense systems requiring robust bus interfacing with dual-register staging capability.
FAQ
What is the maximum operating frequency of the CD74HC646EN?
The CD74HC646EN supports a maximum frequency of 20MHz at 6V over the full -55°C to +125°C range, 25MHz at 4.5V, and 5MHz at 2V. These values reflect guaranteed timing margins under worst-case conditions - actual usable frequency depends on load capacitance, PCB layout, and supply stability. The CD74HC646EN is not rated for continuous operation above these limits without derating.
Does the CD74HC646EN support true bidirectional data flow without external control logic?
Yes, the CD74HC646EN supports fully controlled bidirectional data flow using its DIR (direction) and OE (output enable) inputs. When OE is low, DIR determines whether data flows from A to B (DIR = high) or B to A (DIR = low). The CD74HC646EN requires no external gates or latches to implement this functionality - all control is integrated into the device's logic architecture.
Can the CD74HC646EN store data from both A and B buses simultaneously?
Yes, the CD74HC646EN contains two independent sets of D-type flip-flops - one for the A bus and one for the B bus - allowing concurrent storage of data on both buses. This occurs when OE is high (outputs disabled) and clocks CAB and CBA are asserted, enabling the CD74HC646EN to act as a dual-port register file for bus arbitration or protocol bridging.
Is the CD74HC646EN pin-compatible with other 24-pin HC transceivers like the CD74HC245?
No, the CD74HC646EN is not pin-compatible with CD74HC245 or other octal transceivers. It features unique control pins (CAB, CBA, SAB, SBA) and dual-register architecture absent in simpler transceivers. Pin mapping differs fundamentally - for example, CD74HC245 uses pins 1/19 for OE/DIR only, whereas CD74HC646EN allocates pins 1, 2, 3, 15, and 22 to clock and source-select functions.
What does "NOT RECOMMENDED FOR NEW DESIGNS" mean for the CD74HC646EN?
"NOT RECOMMENDED FOR NEW DESIGNS" indicates Texas Instruments has discontinued active development and long-term supply planning for the CD74HC646EN. While limited stock may exist, TI no longer guarantees future availability. For new projects, engineers should consider SN74HC646N (SOIC) or redesign with functionally equivalent alternatives - the CD74HC646EN remains viable only for legacy repair and continuity builds.
CD74HC646EN Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HC
- Package/Case:
- 24-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:
- 7.8mA, 7.8mA
- Voltage - Supply:
- 2V ~ 6V
- Operating Temperature:
- -55°C ~ 125°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 24-PDIP
CD74HC646EN FAQ
1.How can I place an order for CD74HC646EN through Aetrix?
Please submit a Request for Quotation (RFQ) for CD74HC646EN 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 CD74HC646EN reliable?
The price and inventory of CD74HC646EN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for CD74HC646EN is usually 5 days.
3.What payment methods are accepted for CD74HC646EN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for CD74HC646EN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for CD74HC646EN?
CD74HC646EN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your CD74HC646EN 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 CD74HC646EN?
For technical support, including CD74HC646EN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your CD74HC646EN requirements.
6.How does Aetrix verify that CD74HC646EN is sourced from the original manufacturer or authorized distributors?
All CD74HC646EN 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 CD74HC646EN meets industry standards.
7.What is the process for return or replacement of CD74HC646EN?
All CD74HC646EN units undergo pre-shipment inspection (PSI). If there is an issue with CD74HC646EN, 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 CD74HC646EN part is unused and in its original packaging.
Return procedure for CD74HC646EN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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