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onsemi 74ACQ646SC
- Part No.:
- 74ACQ646SC
- Manufacturer:
- onsemi
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
74ACQ646SC.pdf
- Description:
- IC TXRX NON-INVERT 6V 24SOP
- Quantity:
- Payment:
- Shipping:
Inventory:4,891
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Product details
Overview
74ACQ646SC from Fairchild Semiconductor is an octal registered transceiver with 3-STATE outputs, designed for bidirectional data bus interfacing between A and B buses in high-speed digital systems. It supports real-time transparent transfer and stored-mode register-to-bus transfer, features independent A/B clock inputs (CPAB/CPBA), dual direction control (DIR), and output enable (G). Operating at 2.0–6.0 V, it delivers 24 mA drive strength and guarantees simultaneous switching noise suppression per Quiet Series™ technology.
For engineers reviewing the 74ACQ646SC datasheet, pinout, applications, or equivalent options, this device is selected for synchronous bus isolation, register-retained data routing, and noise-sensitive 3.3 V/5 V mixed-voltage system interconnects where propagation delay (≤9.5 ns @ 5 V), skew (≤1.0 ns), and dynamic threshold stability are critical.
Technical Context
The 74ACQ646SC implements dual 8-bit D-type registers with separate clock inputs CPAB (A→B) and CPBA (B→A), enabling asynchronous loading of data from either bus into its respective register on LOW-to-HIGH clock transitions. Its logic supports four distinct operational modes-real-time A↔B transfer, register load from A or B bus, and register-to-bus output-controlled by DIR, SAB/SBA, and G signals.
It employs Fairchild's Quiet Series™ architecture with GTO™ output control and undershoot correction, plus a split ground bus to minimize simultaneous switching noise. DC input thresholds scale with VCC (VIH = 2.1 V min @ 3.0 V, 3.15 V min @ 4.5 V), and AC timing is specified at CL = 50 pF across −40°C to +85°C.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 2.0 V to 6.0 V - Supports 3.3 V and 5 V logic domains without level shifters. |
| Propagation Delay (Bus-to-Bus) | 2.5 ns (typ), 9.5 ns (max) @ 5 V - Enables sub-10 ns synchronous bus handshaking. |
| Output Drive Strength | ±24 mA - Sustains robust signal integrity driving 50 pF loads across PCB traces. |
| Input Thresholds (VIH/VIL) | VIH = 2.1 V min @ 3.0 V; VIL = 0.9 V max @ 3.0 V - Ensures TTL/CMOS compatibility across voltage grades. |
| Output Skew | ≤1.0 ns (max) - Guarantees deterministic timing alignment across all 8 outputs during parallel switching. |
| Quiescent Supply Current | 8.0 µA (max) @ 5.5 V - Minimizes standby power in battery-backed or low-power hold states. |
| Dynamic Noise Suppression | VOLP ≤ 1.5 V @ 5 V - Limits quiet-output undershoot during simultaneous 8-bit switching events. |
Pinout & Package
74ACQ646SC is housed in a 24-lead Small Outline Integrated Circuit (SOIC) package per JEDEC MS-013, 0.300" wide (Package Number M24B), with standard gull-wing lead form and 1.27 mm pitch.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0–A7 | Data Register A Inputs/Outputs | Bidirectional I/O pins for A-side bus; register-loaded data appears here when enabled. |
| B0–B7 | Data Register B Inputs/Outputs | Bidirectional I/O pins for B-side bus; register-loaded data appears here when enabled. |
| CPAB | Register Clock Input (A→B) | Loads A-bus data into A register and optionally transfers to B-bus on rising edge. |
| CPBA | Register Clock Input (B→A) | Loads B-bus data into B register and optionally transfers to A-bus on rising edge. |
| SAB | Transmit/Receive Control (A→B) | Selects real-time A→B pass-through (SAB = L) or stored A-register→B-bus (SAB = H). |
| SBA | Transmit/Receive Control (B→A) | Selects real-time B→A pass-through (SBA = L) or stored B-register→A-bus (SBA = H). |
| G | Output Enable | Active-Low global 3-STATE control: G = H disables all A/B outputs to high-impedance state. |
| DIR | Direction Control | DIR = H enables A→B data flow; DIR = L enables B→A data flow - determines active bus path. |
Key Features
| Feature | Design Value |
|---|---|
| Quiet Series™ noise suppression | Guaranteed VOLP ≤ 1.5 V and VOHV ≥ −1.2 V under full 8-bit switching - eliminates need for external decoupling beyond standard 0.1 µF per supply pin. |
| Independent A/B register clocks | CPAB and CPBA allow asynchronous capture of A- and B-bus data - essential for handshake-free dual-bus buffering. |
| Multiplexed real-time + stored transfer | Single device performs both transparent bus coupling and register-retained data forwarding - reduces component count vs. discrete transceiver + latch solutions. |
| Split ground bus architecture | Minimizes ground bounce-induced timing jitter - maintains tS/tH setup/hold margins under heavy load conditions. |
| GTO™ output control | Gradual turn-on/turn-off waveform shaping - suppresses EMI peaks above 30 MHz without external RC snubbers. |
Applications
| Backplane Data Routing | Microprocessor Bus Isolation |
|---|---|
Use Scenario: Interfacing CPU local bus to expansion backplane with asynchronous timing domains and mixed-voltage peripherals. IC Role / Device Role / Timing Role: Bidirectional registered transceiver synchronizing data between CPU address/data bus and backplane slots using CPAB/CPBA clocks. Use Value: Eliminates metastability risk via register staging while supporting real-time pass-through during burst transfers - reduces FPGA glue logic by one full register stage. |
Use Scenario: Isolating microcontroller GPIO banks from noisy motor driver or sensor interface circuits. IC Role / Device Role / Timing Role: 3-STATE-controlled bus buffer with independent A/B registers storing safe default states during fault recovery. Use Value: Prevents bus contention during reset sequences; DIR/G/SAB/SBA allow software-configurable direction and latching - no external control logic required. |
| Industrial PLC I/O Module | Digital Signal Processor (DSP) Memory Interface |
Use Scenario: Managing parallel I/O expansion in programmable logic controllers requiring deterministic latency and EMI resilience. IC Role / Device Role / Timing Role: Registered transceiver capturing sensor input data on CPBA edges and forwarding to controller via CPAB-triggered A→B transfer. Use Value: Quiet Series™ ensures reliable operation in electrically noisy factory environments - VOLP < 1.5 V prevents false triggering of downstream comparators or ADC references. |
Use Scenario: Bridging DSP external memory bus (EMIF) to dual-port SRAM or FIFO with write-back caching support. IC Role / Device Role / Timing Role: Storing burst writes in B-register before committing to memory; reading cached data from A-register during read-modify-write cycles. Use Value: Reduces EMIF wait states by decoupling DSP core timing from memory access latency - tPLH ≤ 9.5 ns enables 100+ MHz bus throughput. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal registered transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| 74ACTQ646SC | 5 V-only supply (4.5–5.5 V); faster tPLH (8.5 ns typ); higher VIH/VIL thresholds (2.0 V/0.8 V @ 5 V). | Optimized for strict 5 V TTL systems; not suitable for 3.3 V operation or mixed-voltage designs. | Select 74ACTQ646SC only if system operates exclusively at 5 V and requires marginally lower propagation delay. |
| SN74LVC646APW | 3.3 V only (1.65–3.6 V); LVCMOS levels; 32 mA drive; smaller TSSOP-24 package; no Quiet Series™ noise features. | Targeted at modern low-voltage portable/embedded systems; lacks dynamic noise suppression and split-ground architecture. | Choose SN74LVC646APW for space-constrained 3.3 V designs where EMI is managed at board level, not device level. |
Compared with 74ACQ646SC, 74ACTQ646SC trades wider voltage range for tighter 5 V timing, while SN74LVC646APW sacrifices noise immunity and voltage flexibility for footprint reduction and LVCMOS compatibility - making 74ACQ646SC the sole option for legacy 3.3/5 V mixed-signal industrial backplanes requiring guaranteed simultaneous switching noise control.
Availability
74ACQ646SC is available at Aetrix Electronics and suitable for industrial backplane routing, microprocessor bus isolation, PLC I/O expansion, and DSP memory bridging requiring stable component supply across extended temperature and mixed-voltage operating conditions.
Supply support for 74ACQ646SC 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
Fairchild Semiconductor was a U.S.-based semiconductor company specializing in analog and mixed-signal ICs, acquired by ON Semiconductor in 2016. Its legacy products remain widely deployed in industrial and automotive systems.
The 74ACQ646SC belongs to the Quiet Series™ family of advanced logic devices engineered specifically for noise-critical, high-density digital systems where simultaneous switching noise and timing skew directly impact functional reliability.
FAQ
What is the recommended operating voltage range for the 74ACQ646SC?
The 74ACQ646SC is rated for 2.0 V to 6.0 V supply operation, with guaranteed performance across −40°C to +85°C. At 3.0 V, VIH is 1.5 V min and VOL is 0.44 V max at 24 mA sink; at 5.5 V, VOH reaches 5.4 V min. This range supports direct interfacing with both 3.3 V and 5 V logic families without level translation circuitry.
How does the 74ACQ646SC handle simultaneous switching noise compared to standard AC646 devices?
The 74ACQ646SC integrates Fairchild's Quiet Series™ technology-including GTO™ output control, undershoot correction, and a split ground bus-to guarantee simultaneous switching noise levels below 1.5 V (VOLP) and dynamic threshold stability. Standard AC646 devices lack these features and exhibit significantly higher ground bounce and output undershoot under full 8-bit switching.
Can the 74ACQ646SC operate in both real-time and stored-data modes simultaneously?
No - the 74ACQ646SC operates in one functional mode per control configuration. Real-time (transparent) transfer occurs when SAB/SBA = L; stored-mode transfer activates when SAB/SBA = H. The device cannot concurrently route live bus data and register-stored data on the same A/B path - mode selection is mutually exclusive per direction.
What is the maximum clock frequency supported by the 74ACQ646SC for register loading?
The 74ACQ646SC does not specify a maximum clock frequency; instead, it defines minimum pulse width (tW = 4.0 ns min) and setup/hold times (tS = 3.0 ns, tH = 1.5 ns). With tPLH ≤ 9.5 ns and tPHL ≤ 9.5 ns, reliable register loading is achievable up to approximately 80 MHz in typical 50 pF load conditions - limited by propagation delay and timing margin, not a hard frequency ceiling.
Is the 74ACQ646SC pin-compatible with the 74AC646 or 74ACT646?
No - while functionally similar, the 74ACQ646SC uses identical pinout to the 74AC646 and 74ACT646 (24-pin SOIC), but its internal Quiet Series™ circuitry alters DC and AC behavior. Substituting it into legacy 74AC646 designs may improve noise performance but requires verification of VIH/VIL thresholds and dynamic loading effects due to GTO™ waveform shaping.
74ACQ646SC Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Series:
- 74ACQ
- 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-SOP
74ACQ646SC FAQ
1.How can I place an order for 74ACQ646SC through Aetrix?
Please submit a Request for Quotation (RFQ) for 74ACQ646SC 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 74ACQ646SC reliable?
The price and inventory of 74ACQ646SC are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 74ACQ646SC is usually 5 days.
3.What payment methods are accepted for 74ACQ646SC?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 74ACQ646SC transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for 74ACQ646SC?
74ACQ646SC orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 74ACQ646SC 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 74ACQ646SC?
For technical support, including 74ACQ646SC datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 74ACQ646SC requirements.
6.How does Aetrix verify that 74ACQ646SC is sourced from the original manufacturer or authorized distributors?
All 74ACQ646SC 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 74ACQ646SC meets industry standards.
7.What is the process for return or replacement of 74ACQ646SC?
All 74ACQ646SC units undergo pre-shipment inspection (PSI). If there is an issue with 74ACQ646SC, 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 74ACQ646SC part is unused and in its original packaging.
Return procedure for 74ACQ646SC:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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