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Texas Instruments SN74HCT646DWR
- Part No.:
- SN74HCT646DWR
- Manufacturer:
- Texas Instruments
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74HCT646DWR.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24SOIC
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
SN74HCT646DWR from Texas Instruments is an octal bus transceiver and register IC with 3-state outputs, operating at 4.5 V to 5.5 V, delivering 12 ns typical propagation delay, ±6-mA output drive, and low 80-µA max ICC. It enables bidirectional data flow between A and B buses in industrial control backplanes and legacy system upgrades.
For engineers reviewing the SN74HCT646DWR datasheet, SN74HCT646DWR pinout, SN74HCT646DWR application, or SN74HCT646DWR equivalent, key selection factors include its dual-register architecture for real-time/stored data multiplexing, TTL-compatible inputs, and SOIC-24 package with verified 3-state timing behavior under 50 pF load.
Technical Context
The SN74HCT646DWR integrates independent D-type flip-flop registers for both A and B buses, clocked on low-to-high transitions of CLKAB or CLKBA. Its DIR and OE inputs jointly control direction and output enablement, supporting isolation, real-time transfer, and stored-data transfer modes per the function table.
It features true data paths with no internal inversion, SAB/SBA select controls for transparent vs. registered data routing, and high-current 3-state outputs capable of driving up to 15 LSTTL loads-enabling direct interface with legacy TTL subsystems without level-shifting.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 4.5 V to 5.5 V - compatible with standard 5-V TTL/CMOS logic rails and immune to minor supply droop. |
| Propagation Delay (tpd) | 12 ns typical at 5.5 V, CL = 50 pF - ensures tight timing margins in high-speed bus arbitration circuits. |
| Output Drive | ±6 mA at 5 V - sufficient to directly drive 15 LSTTL loads without external buffers. |
| Input Compatibility | TTL-voltage compatible - accepts standard TTL logic thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V) while powered from 5-V CMOS supply. |
| Quiescent Current | 80 µA max ICC - enables low-static-power operation in always-on bus monitoring or standby interfaces. |
| Operating Temperature | –40°C to +85°C - qualified for industrial ambient environments including factory automation and instrumentation. |
| Package | SOIC-24 (DW) - surface-mount, JEDEC-standard footprint with 1.27-mm pitch, RoHS-compliant NIPDAU finish. |
Pinout & Package
SN74HCT646DWR uses a 24-pin SOIC (DW) package with standard JEDEC outline, 1.27-mm lead pitch, and moisture sensitivity level 1 (260°C peak reflow). Pin numbering follows top-view orientation with Pin 1 at bottom-left corner.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 2, 3, 4, 5, 6, 7, 8 (A1–A8) | A-bus data I/O | Bi-directional data terminals for A-side bus; input when DIR = H and OE = L (A→B), output when DIR = L and OE = L (B→A). |
| 13, 14, 15, 16, 17, 18, 19, 20 (B1–B8) | B-bus data I/O | Bi-directional data terminals for B-side bus; input when DIR = L and OE = L (B→A), output when DIR = H and OE = L (A→B). |
| 21 (OE) | Output Enable | Active-low global 3-state control: OE = H forces all A/B outputs into high-impedance state regardless of DIR or clocks. |
| 3 (DIR) | Direction Control | Determines data flow direction during transceiver mode: DIR = H enables A→B; DIR = L enables B→A. |
| 1 (CLKAB), 23 (CLKBA) | Register Clock Inputs | CLKAB↑ latches A-bus data into A register; CLKBA↑ latches B-bus data into B register - asynchronous to each other. |
| 2 (SAB), 22 (SBA) | Select Controls | SAB selects real-time vs. stored A data onto B bus; SBA selects real-time vs. stored B data onto A bus - enables multiplexed bus access. |
| 9 (GND), 24 (VCC) | Power Supply | Ground reference and 4.5–5.5 V supply rail; decoupling capacitor required within 10 mm of VCC/GND pins for stable switching. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent registers | Separate A and B D-type flip-flop banks allow concurrent storage of data from either bus, enabling time-stamped capture and replay. |
| Multiplexed real-time/stored data paths | SAB/SBA inputs permit dynamic selection between live bus signals and registered values - critical for glitch-free bus arbitration and diagnostic snapshotting. |
| TTL-compatible inputs | Accepts standard TTL logic thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V) while operating from 5-V CMOS supply - eliminates need for input level shifters in mixed-logic systems. |
| High-current 3-state outputs | ±6-mA drive capability supports direct connection to 15 LSTTL loads - reduces component count in legacy backplane interfaces. |
| Low quiescent power | 80-µA max ICC enables use in power-constrained applications such as remote I/O modules where standby current must remain below 100 µA. |
Applications
| Industrial Backplane Interface | Legacy System Bus Extension |
|---|---|
Use Scenario: Interfacing a modern microcontroller unit to an aging 8-bit ISA-style backplane with separate address/data strobes and timing-critical handshaking. IC Role / Device Role / Timing Role: SN74HCT646DWR acts as a bidirectional, register-buffered bus transceiver - isolating MCU timing from backplane skew while preserving signal integrity across long traces. Use Value: Enables deterministic data capture via CLKAB/CLKBA edge-triggered registers and eliminates metastability risk during asynchronous bus handoffs. | Use Scenario: Extending a vintage PLC CPU module's I/O expansion slot with additional sensor/actuator cards using original 5-V TTL signaling standards. IC Role / Device Role / Timing Role: SN74HCT646DWR serves as a bus repeater and data multiplexer - synchronizing legacy peripheral reads/writes while supporting both real-time and buffered access modes. Use Value: Allows hot-swap diagnostics by storing bus state (via SAB/SBA) during fault conditions without disrupting main control loop timing. |
| Automated Test Equipment (ATE) Signal Routing | Embedded Data Acquisition Buffering |
Use Scenario: Routing multiple DUT (device-under-test) parallel data buses through a centralized test head controller with shared resource arbitration. IC Role / Device Role / Timing Role: SN74HCT646DWR functions as a programmable bus switch and sample-hold node - directing test vectors or captured responses based on DIR/OE/SAB control logic. Use Value: Provides sub-15 ns propagation delay and precise setup/hold timing (tsu = 23 ns, th = 5 ns) required for 25+ MHz digital pattern generation. | Use Scenario: Capturing synchronized analog-to-digital converter (ADC) output streams in an isolated measurement module before serial transmission to host processor. IC Role / Device Role / Timing Role: SN74HCT646DWR operates as a parallel data latch and bus interface - clocking ADC samples into its A register on CLKAB↑, then transferring to B bus upon command. Use Value: Eliminates need for external FIFO or microcontroller GPIO bit-banging by providing hardware-managed 8-bit parallel capture with zero software overhead. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver and register applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74HCT640DWR | Octal transceiver only - no internal registers; lacks CLKAB/CLKBA, SAB/SBA, and DIR-controlled stored-data functionality. | Suitable only for simple bidirectional bus buffering without data capture or multiplexing requirements. | Select SN74HCT640DWR only if real-time pass-through suffices and register-based timestamping or diagnostic storage is unnecessary. |
| SN74ACT646DW | Faster AC performance (tPLH/tPHL ≈ 8 ns typ), higher drive (±24 mA), but wider supply range (4.5–5.5 V same); identical pinout and logic function. | Preferred in noise-sensitive or high-speed industrial environments where tighter timing margins and stronger drive are needed. | SN74ACT646DW is a drop-in replacement for SN74HCT646DWR with improved speed and noise immunity - verify layout thermal dissipation for sustained ±24-mA loads. |
Compared with SN74HCT646DWR, SN74HCT640DWR omits register storage and multiplexing controls - limiting it to basic bus isolation - while SN74ACT646DW retains full functional equivalence with enhanced AC specs and drive strength, making it ideal for timing-critical upgrades without PCB revision.
Availability
SN74HCT646DWR is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus extensions, automated test equipment signal routing, and embedded data acquisition buffering requiring stable component supply across extended production lifecycles.
Supply support for SN74HCT646DWR 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The SN74HCT646DWR belongs to TI's 74HCT logic family - designed specifically for 5-V TTL-compatible interfacing in industrial control, instrumentation, and legacy system integration where reliability, timing precision, and mixed-logic compatibility are essential.
FAQ
What is the maximum clock frequency supported by SN74HCT646DWR at 5.5 V?
The SN74HCT646DWR supports a maximum clock frequency of 29 MHz at VCC = 5.5 V and TA = 25°C with CL = 50 pF, as specified in the switching characteristics table. This applies to both CLKAB and CLKBA inputs and assumes proper signal integrity and termination. At full industrial temperature range (–40°C to +85°C), derating to 24 MHz is recommended for robust operation.
Does SN74HCT646DWR require external pull-up resistors on OE for power-up stability?
Yes, SN74HCT646DWR requires OE to be tied to VCC through a pull-up resistor during power-up and power-down to ensure outputs remain in high-impedance state. TI recommends a minimum resistor value determined by the driver's current-sinking capability; typical values range from 4.7 kΩ to 10 kΩ for standard logic drivers, preventing unintended bus contention before firmware initialization.
Can SN74HCT646DWR operate with mixed voltage domains - for example, 3.3-V inputs driving a 5-V SN74HCT646DWR supply?
No, SN74HCT646DWR is not designed for 3.3-V input operation. Its inputs are TTL-voltage compatible (VIH ≥ 2 V, VIL ≤ 0.8 V) but require VCC = 4.5–5.5 V. While 3.3-V logic may meet VIH threshold marginally, it violates recommended operating conditions and risks unreliable switching or increased ICC. A level-shifter or 5-V-compatible driver is required for safe interfacing.
How does the SN74HCT646DWR handle simultaneous clocking of both A and B registers?
The SN74HCT646DWR allows independent, asynchronous clocking of A and B registers via CLKAB↑ and CLKBA↑ transitions. When both clocks trigger on the same edge, data from A bus is latched into the A register and data from B bus into the B register simultaneously - enabling synchronized dual-bus capture without interlock logic or additional timing constraints.
Is SN74HCT646DWR pin-compatible with SN74HCT646DW or SN74HCT646NT?
Yes, SN74HCT646DWR is pin-compatible with SN74HCT646DW and SN74HCT646NT - all share identical 24-pin SOIC (DW) or PDIP (NT) footprints, identical pin numbering, and identical electrical and functional behavior. The "R" suffix denotes tape-and-reel packaging; electrical specs, timing, and logic function are fully identical across these variants.
SN74HCT646DWR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74HCT
- Package/Case:
- 24-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Discontinued at Digi-Key
- 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 ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-SOIC
SN74HCT646DWR FAQ
1.How can I place an order for SN74HCT646DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74HCT646DWR 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 SN74HCT646DWR reliable?
The price and inventory of SN74HCT646DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74HCT646DWR is usually 5 days.
3.What payment methods are accepted for SN74HCT646DWR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74HCT646DWR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74HCT646DWR?
SN74HCT646DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74HCT646DWR 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 SN74HCT646DWR?
For technical support, including SN74HCT646DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74HCT646DWR requirements.
6.How does Aetrix verify that SN74HCT646DWR is sourced from the original manufacturer or authorized distributors?
All SN74HCT646DWR 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 SN74HCT646DWR meets industry standards.
7.What is the process for return or replacement of SN74HCT646DWR?
All SN74HCT646DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74HCT646DWR, 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 SN74HCT646DWR part is unused and in its original packaging.
Return procedure for SN74HCT646DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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