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onsemi MC74AC646DW
- Part No.:
- MC74AC646DW
- Manufacturer:
- onsemi
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
MC74AC646DW.pdf
- Description:
- IC TXRX NON-INVERT 6V 24SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,058
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Product details
Overview
MC74AC646DW from onsemi is an octal registered bus transceiver with non-inverting 3-state outputs, designed for bidirectional data flow control between A and B buses in digital systems. It features independent A/B registers, real-time and stored-data multiplexing, dual clock inputs (CAB/CBA), and supports 24 mA output drive at 5 V. Used in address/data bus isolation and register-controlled I/O expansion in industrial controllers.
For engineers reviewing the MC74AC646DW datasheet, pinout, applications, or equivalent options, key selection criteria include registered bus direction control, simultaneous real-time/stored data routing, 3-state enable timing (tPZH/tPLZ < 13 ns), and SOIC-24 package compatibility with legacy 74AC logic families.
Technical Context
The MC74AC646DW implements dual 8-bit D-type flip-flop registers synchronized to separate LOW-to-HIGH clock edges on CAB and CBA pins, enabling independent capture of A-bus or B-bus data. Its DIR and G inputs jointly control output enable polarity and bus direction, while SAB/SBA select real-time vs. registered data paths.
It operates across 2.0–6.0 V supply range with TTL-compatible input thresholds only in ACT variant - the AC version uses CMOS thresholds (VIH = 2.1 V min at VCC = 3.0 V). Propagation delays are specified down to 1.0 ns (tPHL bus-to-bus at 5 V), supporting high-speed synchronous bus handshaking in microcontroller peripheral interfaces.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74AC - CMOS-compatible, low-power, wide VCC range (2.0–6.0 V) |
| Data Width | Octal (8-bit) bidirectional transceiver with independent A/B register storage |
| Output Drive | ±24 mA at VCC = 5.0 V - sufficient to drive multiple TTL loads or terminated transmission lines |
| Propagation Delay | 1.0–13.5 ns (bus-to-bus or clock-to-bus) - enables ≤70 MHz bus operation under typical conditions |
| 3-State Enable Time | tPZH = 1.5 ns min (G to An/Bn) - supports fast bus arbitration and dynamic reconfiguration |
| Input Thresholds | VIH = 2.1 V @ 3.0 V VCC; VIL = 0.9 V @ 3.0 V - ensures noise margin >0.8 V in 3.3 V systems |
| Package | SOIC-24 (Case 751E), 300 mil width - industry-standard footprint compatible with automated assembly |
Pinout & Package
MC74AC646DW is housed in a 24-pin SOIC (Small Outline Integrated Circuit) package, Case 751E, with 300 mil body width and standard 1.27 mm pitch. Pin 1 is marked by a notch or dot; leads are gull-wing, Pb-free, and rated MSL Level 1.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 23 | CAB / CBA | Separate clock inputs triggering LOW-to-HIGH edge capture into A or B register |
| 2, 22 | SAB / SBA | Select real-time (L) or registered (H) data path for A→B or B→A transfer |
| 3, 21 | DIR / G | DIR sets direction (A→B or B→A); G enables/disables all 3-state outputs |
| 4–11 | A0–A7 | Register A inputs and 3-state outputs - bidirectional I/O pins for A bus |
| 14–21 | B0–B7 | Register B inputs and 3-state outputs - bidirectional I/O pins for B bus |
| 12 | GND | Ground reference for all logic and output stages |
| 24 | VCC | Primary power supply (2.0–6.0 V) for internal logic and output drivers |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B Registers | Enables concurrent capture and hold of data from two separate buses without interference |
| Multiplexed Real-Time + Stored Transfer | Allows seamless switching between live bus traffic and previously latched values via SAB/SBA control |
| Non-Inverting 3-State Outputs | Preserves signal polarity while enabling bus sharing; outputs fully float when disabled (IOZT ≤ ±6 μA) |
| Wide Supply Range | Operates from 2.0 V to 6.0 V - supports mixed-voltage system interfacing (e.g., 3.3 V logic ↔ 5 V peripherals) |
| Pb-Free SOIC-24 Package | Complies with RoHS Directive 2011/65/EU; qualified per JESD22-A114 (HBM ESD >2 kV) |
Applications
| Industrial PLC Backplane Interface | Microcontroller Peripheral Expansion |
|---|---|
Use Scenario: Isolating CPU address/data bus from modular I/O racks in programmable logic controllers. IC Role / Device Role / Timing Role: Registered transceiver buffers and time-aligns burst transfers between processor and field modules using CAB/CBA clocks. Use Value: Prevents bus contention during hot-swap events; registered path ensures deterministic setup/hold timing across variable-length backplane traces. | Use Scenario: Extending GPIO count and data bandwidth for ARM Cortex-M based motor drives. IC Role / Device Role / Timing Role: Bidirectional data shuttle between MCU parallel interface and external ADC/DAC or memory-mapped peripherals. Use Value: Enables zero-wait-state access to external devices via stored-data mode; 24 mA drive sustains signal integrity over 10 cm PCB traces. |
| Legacy System Bus Bridge | Test Equipment Data Acquisition |
Use Scenario: Interfacing modern FPGA-based controllers to legacy 8-bit ISA or VME bus peripherals. IC Role / Device Role / Timing Role: Voltage-level translator and protocol adapter with clock-synchronized register staging. Use Value: Bridges timing domains: FPGA clock domain (100 MHz) ↔ legacy bus (8 MHz) using CAB/CBA edge-triggered latching. | Use Scenario: High-speed digitizer front-end where analog samples are time-stamped and buffered before serial upload. IC Role / Device Role / Timing Role: Captures parallel ADC output words into B-register on sample clock, then forwards to controller via A-bus on system clock. Use Value: Eliminates FIFO logic; real-time + stored modes allow overlapping acquisition and readout without pipeline stalls. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal registered transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ACT646N | Dual 8-bit transceiver with TTL-compatible inputs; identical pinout and function but higher VIH/VIL thresholds (2.0 V/0.8 V @ 5 V) | Better noise immunity in noisy industrial environments; requires ≥4.5 V VCC for guaranteed TTL compatibility | Select SN74ACT646N when interfacing with legacy TTL buses or where input hysteresis is critical. |
| 74LVTH16646DL | 16-bit, 3.3 V-only, LVT enhanced transceiver; different pin count (48-pin TSSOP), no CAB/CBA clocks - uses single clock and latch-enable | Higher density and lower voltage operation; lacks independent A/B register clocks and real-time multiplexing | Choose 74LVTH16646DL only for new 3.3 V designs requiring double-width data paths and simplified control. |
Compared with SN74ACT646N and 74LVTH16646DL, the MC74AC646DW offers unique flexibility in mixed-voltage systems (2.0–6.0 V), precise clock-edge registration for deterministic timing, and true real-time + stored data multiplexing - making it optimal for upgrade paths from 74AC/74ALS logic and legacy bus architectures.
Availability
MC74AC646DW is available at Aetrix Electronics and suitable for industrial PLC backplanes, microcontroller peripheral expansion, and legacy bus bridging requiring stable component supply, long-term lifecycle support, and RoHS-compliant sourcing.
Supply support for MC74AC646DW 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
onsemi (formerly ON Semiconductor) is a global semiconductor supplier focused on energy-efficient innovation for automotive, industrial, cloud, and IoT applications.
The MC74AC646DW belongs to the 74AC logic family - designed for high-speed, low-power, wide-supply-range interfacing in industrial control, test equipment, and legacy system upgrades where reliability and pin compatibility matter.
FAQ
What is the maximum operating supply voltage for the MC74AC646DW?
The MC74AC646DW supports a DC supply voltage (VCC) range of −0.5 V to +7.0 V, with recommended operation from 2.0 V to 6.0 V. Absolute maximum rating is 7.0 V; exceeding this risks permanent damage. At 6.0 V, VOH remains ≥5.4 V and VOL ≤0.44 V under 24 mA load, confirming robust rail-to-rail output swing.
Does the MC74AC646DW support true bidirectional data flow with independent clocking?
Yes, the MC74AC646DW supports true bidirectional operation via separate CAB and CBA clock inputs, each controlling independent 8-bit D-type registers for A and B buses. This allows asynchronous capture of data from either bus on rising clock edges, enabling full-duplex register staging without shared clock constraints.
How does the MC74AC646DW handle bus contention during 3-state transitions?
The MC74AC646DW minimizes bus contention through fast, controlled 3-state enable/disable timing: tPZH/tPLZ (enable) is 1.5–2.5 ns min, and tPHZ/tPLZ (disable) is 1.5–3.5 ns min at 5 V. Combined with low IOZT (±6 μA max), this ensures rapid, low-leakage output isolation - critical for hot-swappable backplane and multi-master bus applications.
Can the MC74AC646DW be used in 3.3 V systems, and what are its input thresholds?
Yes, the MC74AC646DW is fully specified for 3.3 V operation. At VCC = 3.3 V, VIH is guaranteed ≥2.1 V and VIL ≤0.9 V, providing >1.2 V noise margin. Input leakage (IIN) stays below ±1.0 μA, and propagation delay remains ≤13.5 ns - making it ideal for mixed-voltage interfaces between 3.3 V FPGAs and 5 V peripherals.
What is the thermal performance of the MC74AC646DW in SOIC-24 package?
The MC74AC646DW in SOIC-24 (Case 751E) has a junction-to-ambient thermal resistance (θJA) of 59.8 °C/W. At maximum ICC (80 μA) and worst-case output loading (24 mA × 8 channels), total power dissipation remains <150 mW - ensuring junction temperature stays well below 140 °C even at 85 °C ambient, with no heatsink required.
MC74AC646DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Series:
- 74AC
- 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:
- 24mA, 24mA
- Voltage - Supply:
- 2V ~ 6V
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-SOIC
MC74AC646DW FAQ
1.How can I place an order for MC74AC646DW through Aetrix?
Please submit a Request for Quotation (RFQ) for MC74AC646DW 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 MC74AC646DW reliable?
The price and inventory of MC74AC646DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MC74AC646DW is usually 5 days.
3.What payment methods are accepted for MC74AC646DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MC74AC646DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MC74AC646DW?
MC74AC646DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MC74AC646DW 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 MC74AC646DW?
For technical support, including MC74AC646DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MC74AC646DW requirements.
6.How does Aetrix verify that MC74AC646DW is sourced from the original manufacturer or authorized distributors?
All MC74AC646DW 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 MC74AC646DW meets industry standards.
7.What is the process for return or replacement of MC74AC646DW?
All MC74AC646DW units undergo pre-shipment inspection (PSI). If there is an issue with MC74AC646DW, 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 MC74AC646DW part is unused and in its original packaging.
Return procedure for MC74AC646DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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