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onsemi MC74ACT646DWG
- Part No.:
- MC74ACT646DWG
- Manufacturer:
- onsemi
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
MC74ACT646DWG.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,715
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Product details
Overview
MC74ACT646DWG from onsemi is an octal registered transceiver with 3-state outputs, non-inverting data path, TTL-compatible inputs, and dual independent A/B bus registers. It supports real-time or stored-data bidirectional transfer between 8-bit buses, with clock-controlled register loading (CAB/CBA), direction control (DIR), and output enable (G). Used in high-speed bus interface applications requiring data latching and isolation in industrial control backplanes.
For engineers reviewing the MC74ACT646DWG datasheet, pinout, applications, or equivalent options, key selection criteria include 5 V operation, ±24 mA drive strength, 3-state output timing (tPZH/tPLZ < 12 ns), and SOIC-24 package compatibility with legacy 74ACT logic families.
Technical Context
The MC74ACT646DWG implements two independent 8-bit D-type flip-flop registers-one for the A bus (A0–A7) and one for the B bus (B0–B7)-with separate clock inputs CAB and CBA. Data loads on LOW-to-HIGH transitions of either clock, enabling synchronized capture from either bus.
Transmit/receive control is managed via SAB/SBA (select A→B or B→A path) and DIR (data direction), while G (output enable) and DIR jointly determine whether outputs reflect real-time bus data or registered values. All outputs are 3-state, supporting bus sharing without external gating.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 4.5 V to 5.5 V - Ensures compatibility with standard 5 V TTL/CMOS systems and stable operation across industrial temperature range. |
| Output Drive | ±24 mA - Supports direct driving of multiple TTL loads or termination-resistor networks without buffers. |
| Propagation Delay | Max 16 ns (clock-to-bus) - Enables reliable operation in 25+ MHz bus systems with setup/hold margins. |
| Input Compatibility | TTL-level inputs - Accepts standard 0.8 V / 2.0 V thresholds, eliminating level-shifting in mixed-logic designs. |
| 3-State Enable Time | tPZH ≤ 12 ns - Allows fast bus arbitration and minimizes contention windows during multi-master access. |
| Operating Temperature | −40 °C to +85 °C - Qualified for extended industrial environments including factory automation and transportation electronics. |
| Package | SOIC-24 (Case 751E) - Standard surface-mount footprint with 1.27 mm pitch, compatible with automated assembly and IPC-7351B land patterns. |
Pinout & Package
MC74ACT646DWG is housed in a 24-pin SOIC wide-body (SOIC-24 WB) package per Case 751E, with 15.54 mm × 7.60 mm body dimensions, 1.27 mm lead pitch, and Pb-free (RoHS-compliant) finish.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 23 | CAB, CBA | Independent clock inputs triggering load of A→register or B→register on rising edge. |
| 2, 22 | SAB, SBA | Select lines determining real-time A→B or B→A data path when DIR = L and G = L. |
| 3, 21 | DIR, G | DIR sets direction (A↔B); G enables/disables all outputs (active-low 3-state control). |
| 4–11 | A0–A7 | 8-bit A-bus data inputs/outputs - bidirectional I/O pins connected to A-side system bus. |
| 14–20 | B0–B7 | 8-bit B-bus data inputs/outputs - bidirectional I/O pins connected to B-side peripheral or memory bus. |
| 12 | GND | Ground reference for all logic and I/O circuits - must be low-impedance connection to minimize noise coupling. |
| 13 | VCC | +5 V supply - requires local 0.1 μF ceramic decoupling adjacent to pin to suppress switching noise. |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B registers | Enables simultaneous capture and retention of data from two asynchronous buses without cross-talk or timing dependency. |
| Multiplexed real-time/stored transfer | Allows dynamic selection between live bus data and previously latched values-critical for handshake protocols and burst transfers. |
| TTL-compatible inputs | Eliminates need for input level shifters when interfacing with legacy 74LS or microcontroller GPIOs operating at 5 V. |
| 3-state outputs with fast enable/disable | Supports hot-swappable bus segments and reduces signal integrity risk during state transitions (tPHZ/tPLZ ≤ 14.5 ns). |
| Pb-free SOIC-24 package | Meets RoHS Directive 2011/65/EU and JEDEC J-STD-020 moisture sensitivity Level 1 for reflow compatibility. |
Applications
| Industrial Backplane Interface | Microcontroller Bus Expansion |
|---|---|
Use Scenario: Connecting an FPGA-based motion controller to multiple servo drives over a shared 8-bit parallel bus with isolated timing domains. IC Role / Device Role / Timing Role: MC74ACT646DWG acts as a registered bus transceiver, latching command words from the FPGA (A bus) into its internal register on CAB edge, then forwarding them to drive-side peripherals (B bus) under SBA/DIR control. Use Value: Prevents metastability during asynchronous bus handshaking and ensures deterministic timing alignment across distributed nodes. | Use Scenario: Expanding the data/address bus of an 8051 derivative MCU to interface with external SRAM and LCD controller in a medical display module. IC Role / Device Role / Timing Role: MC74ACT646DWG serves as a bidirectional bus buffer with register hold capability-storing address bits during SRAM write cycles while allowing concurrent LCD data updates on the same physical traces. Use Value: Eliminates need for additional address latches and reduces PCB layer count by enabling time-multiplexed bus reuse. |
| Legacy System Emulation | Test Equipment Data Capture |
Use Scenario: Replacing obsolete 74ACT245 in a test fixture that emulates vintage industrial PLC I/O modules using modern FPGA logic. IC Role / Device Role / Timing Role: MC74ACT646DWG provides pin-compatible 3-state buffering with added register functionality-capturing diagnostic scan data from field sensors (B bus) and presenting it to host processor (A bus) on demand. Use Value: Maintains backward electrical and timing behavior while adding traceable data capture capability for firmware validation. | Use Scenario: Capturing parallel digital waveform data from a high-speed ADC evaluation board for offline analysis in automated test systems. IC Role / Device Role / Timing Role: MC74ACT646DWG operates in store-then-transfer mode: sampling ADC output (B bus) on CBA edge, then transferring latched 8-bit samples to acquisition FPGA (A bus) under DIR/G control. Use Value: Decouples ADC sampling clock from system bus clock domain, preventing jitter-induced quantization errors in captured data streams. |
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 in-line package (PDIP-24); identical AC/DC specs but higher thermal resistance (JA = 70 °C/W vs. 59.8 °C/W). | Through-hole assembly only; unsuitable for high-density SMT production or thermally constrained enclosures. | Select SN74ACT646N only for prototyping, repair, or legacy through-hole systems where SOIC footprint is unavailable. |
| 74LVTH16245ADL | 16-bit, non-latching, 3.3 V only; no internal registers; LVTH family with 24 mA drive and 3.3 V TTL-compatible inputs. | Requires external latch for stored-data operation; incompatible with 5 V systems unless level-shifted. | Choose 74LVTH16245ADL only for new 3.3 V designs needing wider bus width and lower power-not a functional replacement for MC74ACT646DWG's register capability. |
Compared with SN74ACT646N and 74LVTH16245ADL, the MC74ACT646DWG uniquely combines 5 V operation, integrated dual 8-bit registers, SOIC-24 packaging, and TTL-compatible inputs-making it the only drop-in solution for upgrading legacy 74ACT bus interfaces requiring latched bidirectional data flow.
Availability
MC74ACT646DWG is available at Aetrix Electronics and suitable for industrial backplane interfaces, microcontroller bus expansion, legacy system emulation, and test equipment data capture requiring stable component supply and long-term manufacturing continuity.
Supply support for MC74ACT646DWG 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 intelligent power systems.
The MC74ACT646DWG belongs to the 74ACT advanced CMOS logic family, designed specifically for high-speed, low-noise 5 V digital interfacing in mission-critical industrial and instrumentation applications.
FAQ
What is the maximum clock frequency supported by the MC74ACT646DWG?
The MC74ACT646DWG does not specify a maximum clock frequency in its datasheet. Instead, timing is defined by minimum pulse width (tw ≥ 7 ns at 5 V) and setup/hold requirements (ts ≥ 7 ns, th ≥ 2.5 ns). Based on propagation delays (tPLH/tPHL ≤ 16 ns) and timing margins, reliable operation up to approximately 25 MHz is achievable in well-designed PCB layouts with controlled impedance and proper decoupling for the MC74ACT646DWG.
Does the MC74ACT646DWG support mixed-voltage operation between A and B buses?
No, the MC74ACT646DWG does not support mixed-voltage operation. It has a single VCC pin (4.5 V to 5.5 V) powering both A and B I/O structures. All inputs and outputs are referenced to this common supply, and the device lacks voltage-level translation circuitry. Interfacing with 3.3 V or other voltage domains requires external level-shifting components for the MC74ACT646DWG.
How does the MC74ACT646DWG handle bus contention during direction switching?
The MC74ACT646DWG prevents bus contention through coordinated 3-state control: outputs are disabled (high-impedance) whenever G = HIGH, regardless of DIR or SAB/SBA states. During direction changes, designers must ensure G is asserted before altering DIR or SAB/SBA to guarantee all outputs enter high-Z before new drivers activate-this sequencing is essential to avoid short-circuits on shared bus lines for the MC74ACT646DWG.
Is the MC74ACT646DWG pin-compatible with the older MC74AC646DWG?
Yes, the MC74ACT646DWG is pin-compatible and functionally compatible with the MC74AC646DWG. Both share identical SOIC-24 pinout, register architecture, and control logic. The primary difference is input threshold compatibility: MC74ACT646DWG features TTL-compatible inputs (VIH = 2.0 V min), while MC74AC646DWG uses CMOS thresholds (VIH = 3.15 V at 4.5 V). This makes MC74ACT646DWG a direct upgrade for systems with marginal input drive strength, without changing layout for the MC74ACT646DWG.
What is the purpose of the SAB and SBA pins on the MC74ACT646DWG?
The SAB (Select A-to-B) and SBA (Select B-to-A) pins on the MC74ACT646DWG determine the real-time data path when DIR = LOW and G = LOW. SAB = LOW enables real-time transfer from A bus to B bus; SBA = LOW enables real-time transfer from B bus to A bus. When both are HIGH, the device enters isolation mode-disabling real-time paths and allowing only registered data transfer controlled by clock edges. These pins provide flexible, software-configurable bus routing independent of direction for the MC74ACT646DWG.
MC74ACT646DWG Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Series:
- 74ACT
- Package/Case:
- 24-SOIC (0.295", 7.50mm Width)
- Packaging:
- Bulk
- 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:
- 4.5V ~ 5.5V
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-SOIC
MC74ACT646DWG FAQ
1.How can I place an order for MC74ACT646DWG through Aetrix?
Please submit a Request for Quotation (RFQ) for MC74ACT646DWG 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 MC74ACT646DWG reliable?
The price and inventory of MC74ACT646DWG are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MC74ACT646DWG is usually 5 days.
3.What payment methods are accepted for MC74ACT646DWG?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MC74ACT646DWG transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MC74ACT646DWG?
MC74ACT646DWG orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MC74ACT646DWG 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 MC74ACT646DWG?
For technical support, including MC74ACT646DWG datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MC74ACT646DWG requirements.
6.How does Aetrix verify that MC74ACT646DWG is sourced from the original manufacturer or authorized distributors?
All MC74ACT646DWG 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 MC74ACT646DWG meets industry standards.
7.What is the process for return or replacement of MC74ACT646DWG?
All MC74ACT646DWG units undergo pre-shipment inspection (PSI). If there is an issue with MC74ACT646DWG, 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 MC74ACT646DWG part is unused and in its original packaging.
Return procedure for MC74ACT646DWG:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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