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onsemi MC74LCX646DT
- Part No.:
- MC74LCX646DT
- Manufacturer:
- onsemi
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- Datasheet:
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MC74LCX646DT.pdf
- Description:
- REGISTERED BUS TRANSCEIVER
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Product details
Overview
MC74LCX646DT from ON Semiconductor is a low-voltage CMOS octal transceiver/registered transceiver operating from 2.3 V to 3.6 V, featuring 5 V-tolerant inputs/outputs, 24 mA balanced output drive, and real-time or registered bidirectional data transfer between A and B buses. It supports memory address driving and TTL-level bus applications with selectable transparent or latched operation.
For engineers reviewing the MC74LCX646DT datasheet, pinout, applications, or equivalent options, key selection criteria include 5 V tolerance for mixed-supply interfacing, dual-clock register control (CAB/CBA), direction-selectable 3-state outputs (DIR/OE), and TSSOP-24 packaging for high-density PCB layouts.
Technical Context
The MC74LCX646DT implements dual independent clocked registers (QA and QB) that capture data on LOW-to-HIGH transitions of CAB (A→B) or CBA (B→A), enabling synchronous storage without external latch logic. Its DIR pin controls data flow direction while OE enables/disables all outputs in 3-state mode.
It integrates select controls (SAB/SBA) to multiplex between real-time (transparent) and stored data paths per bus, supporting isolation, hold, and combined transfer modes as defined in its truth table. The device guarantees IOFF high-impedance state at VCC = 0 V and meets LVTTL/LVCMOS voltage thresholds across −40°C to +85°C.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 2.3 V to 3.6 V - Enables direct interface with 2.5 V/3.3 V logic domains while maintaining compatibility with legacy 5 V peripherals via 5 V-tolerant I/O. |
| Input Voltage Tolerance | −0.5 V to +7.0 V - Allows safe connection to 5 V TTL outputs without level-shifting circuitry or clamping diodes. |
| Output Drive Strength | ±24 mA at VCC ≥ 3.0 V - Sustains robust signal integrity across loaded backplanes or long traces in industrial bus systems. |
| Propagation Delay | 1.5 ns to 9.5 ns (typ/max) - Supports >100 MHz clock rates in high-speed data transfer applications such as memory expansion interfaces. |
| Quiescent Supply Current | 10 μA - Minimizes standby power in battery-backed or energy-sensitive embedded systems. |
| IOFF Leakage | 10 μA at VCC = 0 V - Ensures true high-impedance isolation during hot-swap or power sequencing events. |
| ESD Rating | HBM >2000 V, MM >200 V - Provides built-in protection against handling damage without requiring external ESD components. |
Pinout & Package
MC74LCX646DT is housed in a 24-lead plastic TSSOP package (Case 948H), measuring 7.6 mm × 4.4 mm × 1.2 mm, optimized for automated assembly and space-constrained designs.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0–A7 | Side A bidirectional I/O | Connects to local processor or controller bus; functions as input or output depending on DIR/OE state and register mode. |
| B0–B7 | Side B bidirectional I/O | Interfaces with peripheral or memory bus; supports simultaneous storage and real-time transfer when configured with SAB/SBA. |
| CAB | Register clock (A→B) | Triggers capture of A-port data into QA register on LOW-to-HIGH edge; active regardless of OE/DIR state. |
| CBA | Register clock (B→A) | Triggers capture of B-port data into QB register on LOW-to-HIGH edge; operates independently of CAB. |
| SAB | Select control (A→B path) | Chooses between real-time A data or QA-stored data routed to B bus when OE is active. |
| SBA | Select control (B→A path) | Chooses between real-time B data or QB-stored data routed to A bus when OE is active. |
| DIR | Direction control | Determines primary data flow direction: HIGH = A→B, LOW = B→A; overrides SAB/SBA in isolation mode. |
| OE | Output enable (active LOW) | Enables 3-state outputs on both A and B ports when LOW; places all I/Os in high-Z when HIGH. |
| VCC | Power supply | 2.3–3.6 V digital supply; powers internal logic and output drivers; requires local decoupling. |
| GND | Ground reference | Common return path for all signals and supply current; must be low-impedance for noise immunity. |
Key Features
| Feature | Design Value |
|---|---|
| 5 V-tolerant I/O | Enables seamless integration between 3.3 V system logic and legacy 5 V peripherals without external level shifters. |
| Dual independent register clocks (CAB/CBA) | Allows asynchronous latching of data on either bus side, supporting time-multiplexed or buffered interconnect architectures. |
| Selectable transparent/register modes (SAB/SBA) | Permits dynamic switching between immediate pass-through and synchronized storage behavior within the same device. |
| IOFF protection at VCC = 0 V | Prevents back-driving of powered-down sections during live insertion or partial system reset sequences. |
| 24 mA balanced output drive | Delivers symmetrical rise/fall times and stable termination under heavy capacitive loads typical in multi-drop bus environments. |
| Low ICC quiescent current (10 μA) | Reduces total system power budget in always-on subsystems such as watchdog controllers or configuration managers. |
Applications
| Memory Address Buffering | Industrial Backplane Interface |
|---|---|
Use Scenario: Driving address lines from a 3.3 V microcontroller to multiple 5 V SRAM or EPROM devices on a shared bus. IC Role / Device Role / Timing Role: Bidirectional address transceiver with registered hold capability to synchronize address setup before memory access cycles. Use Value: Eliminates need for discrete level shifters and external latches while ensuring timing margin compliance with slow 5 V memory access times. |
Use Scenario: Interfacing a 2.5 V FPGA I/O bank to a 5 V PLC I/O module over a 24-pin parallel backplane. IC Role / Device Role / Timing Role: Voltage-tolerant bus transceiver providing direction-controlled, noise-immune data exchange with configurable latency. Use Value: Maintains signal integrity across noisy industrial environments and simplifies board-level voltage domain partitioning. |
| Hot-Swappable Module Bridge | Legacy Peripheral Adapter |
Use Scenario: Enabling safe insertion/removal of a 3.3 V communication module into a powered 5 V chassis backplane. IC Role / Device Role / Timing Role: Isolation-capable transceiver with IOFF support to prevent bus contention during plug-in/out sequences. Use Value: Guarantees zero-current injection into live backplane lines, meeting IEC 61000-4-2 Class 3 ESD and hot-swap safety requirements. |
Use Scenario: Connecting a modern ARM-based SoM to legacy ISA-bus peripherals requiring 5 V signaling and register-controlled handshaking. IC Role / Device Role / Timing Role: Registered transceiver implementing strobe-synchronized data capture and controlled output enable timing. Use Value: Replaces discrete 74-series latch+buffer combinations, reducing component count and improving timing predictability. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal registered transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LVC8T245RHLR | Single-directional 8-bit transceiver with auto-direction sensing; no internal registers or dual-clock capability. | Lacks register storage and independent A/B clocking; suitable only for simple level-shifted bus extension. | Select when transparent translation suffices and register functionality is unnecessary. |
| 74ALVC164245PAG | 16-bit version in TSSOP-48; higher pin count, identical 2.3–3.6 V range and 5 V tolerance but no SAB/SBA select logic. | Provides double data width but omits multiplexed real-time/stored path selection; limited to basic bidirectional buffering. | Choose for wider bus widths where register control is managed externally. |
Compared with SN74LVC8T245RHLR and 74ALVC164245PAG, the MC74LCX646DT uniquely combines 5 V-tolerant I/O, dual-register clocking, and SAB/SBA multiplexing in a compact 24-pin TSSOP-enabling advanced bus arbitration and synchronization not possible with simpler transceivers.
Availability
MC74LCX646DT is available at Aetrix Electronics and suitable for memory address buffering, industrial backplane interfacing, and hot-swappable module bridging requiring stable component supply, long-term lifecycle assurance, and consistent parametric performance.
Supply support for MC74LCX646DT 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
ON Semiconductor is a global semiconductor manufacturer specializing in power management, analog, sensor, and logic solutions for automotive, industrial, and communications markets.
The MC74LCX646DT belongs to the LCX low-voltage CMOS logic family, designed specifically for mixed-voltage system interfacing where 3.3 V core logic must reliably communicate with 5 V legacy infrastructure.
FAQ
What is the maximum clock frequency supported by the MC74LCX646DT?
The MC74LCX646DT supports a maximum clock pulse frequency of 150 MHz at VCC = 3.0 V to 3.6 V, as specified in its AC characteristics table. This allows reliable operation in high-speed data transfer scenarios such as memory-mapped I/O or fast peripheral bridging. The actual achievable frequency depends on load capacitance, trace routing, and supply stability - design validation using the recommended 50 pF load and 500 Ω termination is advised for timing-critical implementations of the MC74LCX646DT.
Does the MC74LCX646DT support live insertion into a powered system?
Yes, the MC74LCX646DT supports live insertion and withdrawal due to its IOFF specification, which guarantees high-impedance I/O states when VCC = 0 V. This prevents current backflow into powered bus lines during hot-plug events. The device also features 5 V-tolerant inputs/outputs and robust ESD protection (>2000 V HBM), making it suitable for modular systems like telecom line cards or industrial I/O carriers where field-replaceable units require safe in-service replacement - a key reliability feature of the MC74LCX646DT.
How does the MC74LCX646DT handle direction control and output enable simultaneously?
The MC74LCX646DT uses separate DIR (direction) and OE (output enable) pins for independent control: DIR sets the primary data flow direction (A→B or B→A), while OE globally enables or disables all outputs in 3-state mode. When OE is HIGH, both A and B ports enter high-impedance regardless of DIR state - enabling bus isolation. When OE is LOW, DIR determines which port drives data, and SAB/SBA selects between real-time or registered data sources. This layered control architecture gives precise timing and functional flexibility in complex bus architectures using the MC74LCX646DT.
Can the MC74LCX646DT operate with a 2.5 V supply?
Yes, the MC74LCX646DT is fully specified to operate from 2.3 V to 3.6 V, including 2.5 V nominal supplies. At VCC = 2.5 V, DC parameters such as VIH (2.0 V min), VOL (0.4 V max at 12 mA), and ICC (10 μA) remain valid per the Recommended Operating Conditions table. AC performance degrades slightly - propagation delays increase and maximum clock frequency reduces - but the device maintains full functionality and logic compatibility. System designers using 2.5 V rails can confidently deploy the MC74LCX646DT without derating concerns.
What is the function of the SAB and SBA pins on the MC74LCX646DT?
The SAB (Select A to B) and SBA (Select B to A) pins on the MC74LCX646DT control multiplexing between real-time (transparent) and registered data paths. When SAB = LOW, real-time A-port data passes directly to the B bus; when SAB = HIGH, QA-register-stored data appears on B. Similarly, SBA selects between real-time B data or QB-stored data for the A bus. These pins enable dynamic reconfiguration of data flow behavior without changing clocking or direction settings - a critical capability for adaptive bus protocols implemented with the MC74LCX646DT.
MC74LCX646DT Specifications
- Product attributes
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- Manufacturer:
- onsemi
- Series:
- *
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- Bulk
- Product Status:
- Active
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MC74LCX646DT FAQ
1.How can I place an order for MC74LCX646DT through Aetrix?
Please submit a Request for Quotation (RFQ) for MC74LCX646DT 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 MC74LCX646DT reliable?
The price and inventory of MC74LCX646DT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MC74LCX646DT is usually 5 days.
3.What payment methods are accepted for MC74LCX646DT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MC74LCX646DT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for MC74LCX646DT?
MC74LCX646DT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your MC74LCX646DT 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 MC74LCX646DT?
For technical support, including MC74LCX646DT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MC74LCX646DT requirements.
6.How does Aetrix verify that MC74LCX646DT is sourced from the original manufacturer or authorized distributors?
All MC74LCX646DT 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 MC74LCX646DT meets industry standards.
7.What is the process for return or replacement of MC74LCX646DT?
All MC74LCX646DT units undergo pre-shipment inspection (PSI). If there is an issue with MC74LCX646DT, 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 MC74LCX646DT part is unused and in its original packaging.
Return procedure for MC74LCX646DT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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