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Texas Instruments CD74HC646M
- Part No.:
- CD74HC646M
- Manufacturer:
- Texas Instruments
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
CD74HC646M.pdf
- Description:
- IC TXRX NON-INVERT 6V 24SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:4,582
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Product details
Overview
CD74HC646M from Texas Instruments is an octal bus transceiver/register with three-state non-inverting outputs, featuring independent A/B bus registers, direction-controlled bidirectional data flow, and clocked D-type flip-flop storage. It operates from 2V to 6V, delivers 12ns typical propagation delay (A↔B) at 5V/15pF, and supports -55°C to +125°C industrial/military temperature range - used in high-reliability board-level data path arbitration and register-retentive bus interfacing.
For engineers reviewing the CD74HC646M datasheet, CD74HC646M pinout, CD74HC646M application, or CD74HC646M equivalent, key selection criteria include its dual-clock (CAB/CBA) register control, SAB/SBA source multiplexing, OE/DIR-driven output enable and direction logic, and SOIC-24 package compatibility with legacy HC logic systems.
Technical Context
The CD74HC646M implements edge-triggered D-type flip-flops for both A and B buses, with separate CAB and CBA clocks enabling independent latching of data from either bus on low-to-high transitions. Its DIR input selects real-time or stored data directionality, while OE disables all outputs into high-impedance state regardless of DIR or clock activity.
Three-state output drivers support 15 LSTTL loads, with balanced tPLH/tPHL propagation (≤35ns at 6V/50pF) and fast transition times (≤15ns at 6V). The SAB and SBA select inputs allow dynamic routing between transparent (real-time) and registered (stored) data paths without requiring external latches.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 2V to 6V - enables interoperability with 3.3V and 5V logic domains without level shifters. |
| Propagation Delay (A↔B) | 12ns typical at VCC = 5V, CL = 15pF - ensures tight timing budgets in synchronous bus handshaking. |
| Operating Temperature | -55°C to +125°C - qualified for aerospace, defense, and under-hood automotive control modules. |
| Output Drive Strength | 15 LSTTL loads - sufficient to drive long PCB traces or multiple downstream HC/HCT inputs. |
| Input Noise Immunity | NIL = NIH = 30% of VCC at 5V - robust against ground bounce and supply ripple in noisy environments. |
| Three-State Leakage | ±5µA max at -55°C to +125°C - minimizes standby current in powered-down subsystems. |
| Max Clock Frequency | 23MHz at VCC = 6V, TA = -55°C to +125°C - supports reliable register update rates in deterministic control loops. |
Pinout & Package
CD74HC646M is housed in a 24-lead SOIC (Small Outline Integrated Circuit) package with standard 0.300-inch body width and 1.27mm lead pitch. Pin 12 is GND; Pin 24 is VCC. Thermal resistance θJA = 46°C/W enables operation up to 125°C ambient without forced airflow.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 CAB | Register Clock A→B | Low-to-high edge clocks A-bus data into internal DFFs for later B-bus output. |
| 2 SAB | Source Select A-B Path | Selects whether A→B output reflects real-time A data (SAB = L) or stored A data (SAB = H). |
| 3 DIR | Direction Control | DIR = L enables A-bus outputs; DIR = H enables B-bus outputs - defines active data path. |
| 4–11 A0–A7 | A-Bus I/O Terminals | Bidirectional data lines; high-impedance when OE = H or DIR mismatch disables A-side output. |
| 12 GND | Ground Reference | Primary return path for all logic and switching currents; must be low-inductance connection. |
| 13 VCC | Power Supply | 2V–6V CMOS supply; bypass capacitor (0.1µF) required within 10mm of this pin. |
| 14 SBA | Source Select B-A Path | Selects whether B→A output reflects real-time B data (SBA = L) or stored B data (SBA = H). |
| 15 OE | Output Enable | OE = L enables transceiver outputs; OE = H forces all A/B pins into high-Z - critical for bus sharing. |
| 16–23 B0–B7 | B-Bus I/O Terminals | Bidirectional data lines; driven only when OE = L and DIR matches bus direction. |
| 24 CBA | Register Clock B→A | Low-to-high edge clocks B-bus data into internal DFFs for later A-bus output. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent register clocks (CAB, CBA) | Enables asynchronous capture of A and B bus data without shared timing constraints. |
| SAB/SBA source multiplexing | Allows per-path selection between live and registered data - eliminates need for external MUX logic. |
| Non-inverting three-state outputs | Preserves signal polarity across bidirectional paths while supporting hot-swap bus arbitration. |
| 10 LSTTL fanout over full temp range | Guarantees drive capability across -55°C to +125°C without derating - essential for unregulated environments. |
| High noise immunity (30% VCC) | Reduces false triggering in electrically noisy systems such as motor drives or power converters. |
Applications
| Industrial PLC Backplane Interface | Military Avionics Data Bus Arbitration |
|---|---|
|
Use Scenario: Interfacing microcontroller local bus to modular I/O backplane with mixed-voltage peripherals. IC Role / Device Role / Timing Role: Bidirectional octal transceiver with register retention, synchronizing asynchronous module reads/writes via CAB/CBA clocks. Use Value: Eliminates external latch + buffer combinations; SAB/SBA allows selective use of real-time vs. registered data during fault recovery sequences. |
Use Scenario: Isolating and routing sensor telemetry between flight computer and redundant sensor suites in UAVs. IC Role / Device Role / Timing Role: High-reliability bus register/transceiver operating across -55°C to +125°C with radiation-tolerant HC process. Use Value: Enables deterministic timestamping of sensor data via clocked register capture, independent of bus contention timing. |
| Automotive Engine Control Unit (ECU) Diagnostics Port | Test Equipment Digital Pattern Generator |
|
Use Scenario: Providing isolated, direction-controlled access to ECU internal data buses during OBD-II diagnostics. IC Role / Device Role / Timing Role: Three-state transceiver with OE/DIR control, allowing diagnostic tool to safely drive or monitor bus without disrupting ECU operation. Use Value: Prevents bus contention during live debugging; high-impedance mode (OE = H) isolates tool from running ECU firmware. |
Use Scenario: Generating synchronized stimulus patterns for IC functional testing with programmable data hold and direction switching. IC Role / Device Role / Timing Role: Register-based pattern repeater with independent A/B clocks and source-select multiplexing. Use Value: Reduces test system FPGA resource usage by offloading pattern registration and routing to dedicated logic. |
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 | Dual-in-line (PDIP-24) package; identical electrical specs but higher θJA (70°C/W) and no surface-mount compatibility. | Preferred for prototyping or through-hole legacy systems; unsuitable for automated SMT assembly. | Select SN74HC646N only when manual assembly or socket-based validation is required. |
| CD74HCT646M | TTL-compatible input thresholds (VIH = 2V min); same pinout and function but requires ≥4.5V for guaranteed 5V TTL interface. | Used where interfacing with legacy 5V TTL peripherals; not suitable for mixed 3.3V/5V systems without level translation. | Choose CD74HCT646M only when direct connection to standard TTL outputs is mandatory. |
Compared with CD74HC646M, SN74HC646N trades surface-mount reliability for breadboard flexibility, while CD74HCT646M sacrifices wide-voltage operation for guaranteed TTL input compatibility - making CD74HC646M optimal for modern mixed-supply industrial designs requiring SOIC packaging and 2V–6V operation.
Availability
CD74HC646M is available at Aetrix Electronics and suitable for industrial PLC backplanes, military avionics data buses, and automotive ECU diagnostics requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for CD74HC646M 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 decades of heritage in high-reliability logic families.
The CD74HC646M belongs to TI's High-Speed CMOS (HC) logic portfolio, designed for low-power, wide-voltage, high-noise-immunity digital interfacing in harsh-environment applications.
FAQ
What is the maximum clock frequency supported by CD74HC646M across its full temperature range?
The CD74HC646M supports up to 23MHz maximum clock frequency at VCC = 6V and over the full -55°C to +125°C operating range. This value is specified in the Switching Specifications table under fMAX for HC types at the extreme temperature condition, ensuring deterministic register updates in time-critical control applications without derating.
Does CD74HC646M support true bidirectional data flow without external direction control logic?
Yes, CD74HC646M integrates full bidirectional control via its DIR pin: when DIR = L, A-bus outputs are enabled and B-bus inputs are active; when DIR = H, B-bus outputs are enabled and A-bus inputs are active. This eliminates need for external direction logic, simplifying PCB layout and reducing component count in bus arbitration circuits.
Can CD74HC646M operate reliably at 3.3V supply voltage?
Yes, CD74HC646M is fully specified for 2V to 6V operation, including 3.3V. At VCC = 3.3V, VIH = 2.31V min and VIL = 1.09V max ensure compatibility with standard 3.3V CMOS outputs, and propagation delay remains within usable limits (tPLH/tPHL ≤ 66ns at 3.3V/50pF), making it suitable for mixed-voltage system interfaces.
How does the SAB and SBA pin functionality differ from standard bus transceivers?
Unlike basic transceivers, CD74HC646M's SAB and SBA pins enable dynamic selection between real-time and registered data paths: SAB = L routes live A-bus data to B-bus; SAB = H routes previously clocked A-register data. This provides on-the-fly data staging without external registers, enhancing determinism in diagnostic or fail-safe data routing.
Is CD74HC646M pin-compatible with other members of the HC646 family?
Yes, CD74HC646M shares identical pinout and function with CD74HC646M96 (tape-and-reel variant) and CD74HC646E (ceramic DIP), and is functionally compatible with SN74HC646N (same pinout, different package). All variants implement identical logic, timing, and electrical behavior per the SCHS193A datasheet.
CD74HC646M Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HC
- 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:
- 7.8mA, 7.8mA
- Voltage - Supply:
- 2V ~ 6V
- Operating Temperature:
- -55°C ~ 125°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-SOIC
CD74HC646M FAQ
1.How can I place an order for CD74HC646M through Aetrix?
Please submit a Request for Quotation (RFQ) for CD74HC646M 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 CD74HC646M reliable?
The price and inventory of CD74HC646M are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for CD74HC646M is usually 5 days.
3.What payment methods are accepted for CD74HC646M?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for CD74HC646M transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for CD74HC646M?
CD74HC646M orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your CD74HC646M 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 CD74HC646M?
For technical support, including CD74HC646M datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your CD74HC646M requirements.
6.How does Aetrix verify that CD74HC646M is sourced from the original manufacturer or authorized distributors?
All CD74HC646M 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 CD74HC646M meets industry standards.
7.What is the process for return or replacement of CD74HC646M?
All CD74HC646M units undergo pre-shipment inspection (PSI). If there is an issue with CD74HC646M, 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 CD74HC646M part is unused and in its original packaging.
Return procedure for CD74HC646M:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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