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onsemi MC74AC646DWR2G
- Part No.:
- MC74AC646DWR2G
- Manufacturer:
- onsemi
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
MC74AC646DWR2G.pdf
- Description:
- IC TXRX NON-INVERT 6V 24SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,414
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Product details
Overview
MC74AC646DWR2G from onsemi is an octal registered bus transceiver with non-inverting 3-state outputs, designed for bidirectional data flow between A and B buses in high-speed digital systems. It features independent A/B registers, real-time and stored-data transfer modes, 24 mA output drive, and operates across 2.0–6.0 V supply range. Used in address/data bus isolation and latch-controlled I/O expansion in industrial controllers and legacy computing interfaces.
For engineers reviewing the MC74AC646DWR2G datasheet, pinout, applications, or equivalent options, key selection criteria include clock-controlled register loading (CAB/CBA), dual-direction transmit/receive control (SAB/SBA), output enable logic (DIR/G), and SOIC-24 package compatibility with legacy 74AC logic families.
Technical Context
The MC74AC646DWR2G implements two independent 8-bit D-type flip-flop registers-one per bus-enabling synchronous capture of A or B bus data on LOW-to-HIGH clock transitions. Its multiplexed output stage allows real-time or registered data routing to either bus under SAB/SBA and DIR control.
Logic-level translation is not supported: inputs are CMOS-compatible (VIH = 2.1 V min at VCC = 3.0 V), outputs swing rail-to-rail, and propagation delays range from 1.5 ns (bus-to-bus, 5 V) to 18.5 ns (clock-to-bus, 3.3 V). The device lacks internal pull-ups, hysteresis, or slew-rate control.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 2.0 V to 6.0 V - supports mixed-voltage system interfacing and battery-backed operation down to 2.0 V |
| Output Drive Strength | ±24 mA - sufficient to drive 50 pF loads with <13 ns propagation delay at 5 V, enabling direct connection to standard TTL/CMOS loads |
| Propagation Delay (Bus-to-Bus) | 1.0 ns min / 9.0 ns max at 5 V - enables sub-10 ns transparent data path switching critical for cycle-accurate bus arbitration |
| 3-State Enable/Disable Time | tPZH/tPLZ = 1.5–9.0 ns at 5 V - ensures fast bus release and prevents contention during multi-master access |
| Input Thresholds (VCC = 5 V) | VIH = 2.75 V, VIL = 1.65 V - provides 0.8 V noise margin against ground bounce and crosstalk in dense PCB layouts |
| Quiescent Supply Current | 80 μA max - enables low-static-power operation in always-on control logic without thermal derating |
| Operating Temperature | −40 °C to +85 °C - qualified for industrial automation, motor drives, and outdoor embedded equipment |
Pinout & Package
MC74AC646DWR2G is housed in a Pb-free SOIC-24 wide-body package (Case 751E), 15.4 mm × 7.5 mm footprint, 2.35–2.65 mm height, 1.27 mm pitch, with gull-wing leads suitable for reflow soldering.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 23 | CAB, CBA | Asynchronous clock inputs - LOW-to-HIGH edge loads A→B or B→A bus data into respective registers |
| 2, 22 | SAB, SBA | Transmit/receive select - controls direction of real-time or registered data flow between buses |
| 3, 21 | DIR, G | Output enable pair - DIR selects bus direction; G enables/disables all 3-state outputs simultaneously |
| 4–11 | A0–A7 | Register A inputs/outputs - bidirectional I/O pins connected to A-side bus; register contents appear when enabled |
| 14–20 | B0–B7 | Register B inputs/outputs - bidirectional I/O pins connected to B-side bus; register contents appear when enabled |
| 12 | GND | Ground reference - must be low-impedance connection to minimize switching noise coupling into register clocks |
| 24 | VCC | Power supply - bypass capacitor (0.1 μF ceramic) required within 5 mm for stable register operation |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B Registers | Enables concurrent storage of two 8-bit data words - eliminates need for external latches in dual-bus arbitration logic |
| Multiplexed Real-Time + Stored Transfer | Single device supports both immediate pass-through and clock-synchronized data forwarding - reduces component count in protocol bridge designs |
| Non-Inverting 3-State Outputs | Prevents bus contention during hot-swap or power sequencing - outputs enter high-Z state within 10 ns of G assertion |
| 24 mA Output Sink/Source | Drives standard 50 Ω transmission lines or multiple 74AC inputs without external buffers - simplifies backplane interface design |
| Pb-Free SOIC-24 Package | Complies with RoHS Directive 2011/65/EU and JEDEC J-STD-020 moisture sensitivity level 1 - supports lead-free reflow assembly |
Applications
| Industrial PLC Backplane Interface | Legacy ISA Bus Expansion |
|---|---|
Use Scenario: Isolating CPU address/data bus from modular I/O cards in programmable logic controllers. IC Role / Device Role / Timing Role: Registered transceiver synchronizing burst-mode data transfers between CPU and field I/O modules using CAB/CBA clocks. Use Value: Eliminates timing skew between parallel bus segments via register staging, enabling reliable 10 MHz bus operation over 15 cm traces. |
Use Scenario: Adding memory-mapped peripheral slots to retro-computing platforms using ISA bus architecture. IC Role / Device Role / Timing Role: Bidirectional bus buffer with latch capability, allowing ISA master to read/write expansion card registers without bus contention. Use Value: Provides deterministic 3-state control (via DIR/G) and 24 mA drive to meet ISA specification load requirements across 8-bit data paths. |
| Automated Test Equipment (ATE) Signal Routing | Embedded Controller Address Latching |
Use Scenario: Dynamic reconfiguration of signal paths between DUT interface and measurement instruments in modular ATE racks. IC Role / Device Role / Timing Role: Register-controlled multiplexer selecting between real-time sensor data or pre-loaded test patterns routed to DUT pins. Use Value: Enables glitch-free switching between live and stored vectors using SAB/SBA control, critical for functional test pattern integrity. |
Use Scenario: Latching 16-bit address bus in microcontroller-based motor drives where external memory or peripherals require stable address hold. IC Role / Device Role / Timing Role: Address register capturing upper/lower byte on separate clock edges (CAB/CBA), decoupling MCU core timing from peripheral access latency. Use Value: Reduces address setup time violations by 4.5 ns versus direct bus connection, improving timing margin for 25 MHz MCU operation. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal registered transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74AC646N | Dual in-line package (PDIP-24); identical AC electrical specs but 300 mil body width vs. SOIC-24's 300 mil width; no Pb-free guarantee | Preferred for through-hole prototyping or legacy board repair where SOIC footprint unavailable | Select SN74AC646N only when manual soldering or socket-based testing is required; not recommended for automated SMT production. |
| MC74ACT646DWR2G | TTL-compatible inputs (VIH = 2.0 V @ 5 V); otherwise identical pinout, timing, and drive strength; same SOIC-24 package | Required when interfacing with legacy 74LS/74ALS logic where AC input thresholds would cause marginal recognition | Choose MC74ACT646DWR2G only if driving 74LS-family devices; otherwise MC74AC646DWR2G offers superior noise immunity in mixed-logic systems. |
Compared with SN74AC646N and MC74ACT646DWR2G, the MC74AC646DWR2G delivers optimal noise margin for modern CMOS systems, smallest PCB footprint among functionally equivalent transceivers, and guaranteed Pb-free compliance - making it the preferred choice for new industrial and automotive control designs requiring long-term supply stability.
Availability
MC74AC646DWR2G is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy ISA expansion modules, automated test equipment signal routing, and embedded controller address latching requiring stable component supply across extended product lifecycles.
Supply support for MC74AC646DWR2G 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, with manufacturing and R&D operations across Asia, North America, and Europe.
The MC74AC646DWR2G belongs to the 74AC logic family - engineered for high-speed, low-power, pin-compatible upgrades to legacy 74LS and 74F logic in industrial control, instrumentation, and communications infrastructure.
FAQ
What is the maximum clock frequency supported by MC74AC646DWR2G?
The MC74AC646DWR2G does not specify a maximum clock frequency; instead, its timing is governed by minimum pulse width (tw = 3.5 ns min at 5 V) and setup/hold requirements (ts = 4.0 ns, th = 0.5 ns at 5 V). For reliable register loading, the effective maximum clock rate is approximately 100 MHz under typical 5 V conditions, assuming clean signal integrity and proper load capacitance management.
Does MC74AC646DWR2G support mixed-voltage operation between A and B buses?
No, the MC74AC646DWR2G has a single VCC pin and shares common logic thresholds across all I/Os. Both A and B buses must operate at the same supply voltage (2.0–6.0 V). It cannot translate between different voltage domains - for level-shifting applications, discrete translators or dedicated level-shifters are required alongside MC74AC646DWR2G.
Can MC74AC646DWR2G be used without connecting the GND pin?
No - the MC74AC646DWR2G requires a solid, low-impedance connection to GND (Pin 12) for correct internal biasing and register operation. Omitting or floating GND will result in undefined logic states, excessive ICC current, potential latch-up, and permanent device damage. Always connect GND before applying VCC or any input signals.
What is the purpose of the SAB and SBA pins on MC74AC646DWR2G?
The SAB and SBA pins on MC74AC646DWR2G control data direction and source selection: SAB enables A→B transfers (real-time or registered), while SBA enables B→A transfers. When both are HIGH, outputs enter high-impedance state regardless of DIR/G status. These pins allow independent control of each bus direction without requiring external logic gates.
Is MC74AC646DWR2G pin-compatible with MC74ACT646DWR2G?
Yes - MC74AC646DWR2G and MC74ACT646DWR2G share identical SOIC-24 pinout, package dimensions, and functional block diagram. The only difference is input threshold compatibility: MC74ACT646DWR2G accepts TTL-level inputs (VIH = 2.0 V), while MC74AC646DWR2G requires higher CMOS thresholds (VIH = 2.75 V at 5 V). Swapping them requires verifying upstream driver logic levels.
MC74AC646DWR2G Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Series:
- 74AC
- Package/Case:
- 24-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- 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
MC74AC646DWR2G FAQ
1.How can I place an order for MC74AC646DWR2G through Aetrix?
Please submit a Request for Quotation (RFQ) for MC74AC646DWR2G 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 MC74AC646DWR2G reliable?
The price and inventory of MC74AC646DWR2G are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MC74AC646DWR2G is usually 5 days.
3.What payment methods are accepted for MC74AC646DWR2G?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MC74AC646DWR2G transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MC74AC646DWR2G?
MC74AC646DWR2G orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MC74AC646DWR2G 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 MC74AC646DWR2G?
For technical support, including MC74AC646DWR2G datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MC74AC646DWR2G requirements.
6.How does Aetrix verify that MC74AC646DWR2G is sourced from the original manufacturer or authorized distributors?
All MC74AC646DWR2G 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 MC74AC646DWR2G meets industry standards.
7.What is the process for return or replacement of MC74AC646DWR2G?
All MC74AC646DWR2G units undergo pre-shipment inspection (PSI). If there is an issue with MC74AC646DWR2G, 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 MC74AC646DWR2G part is unused and in its original packaging.
Return procedure for MC74AC646DWR2G:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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