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onsemi 74LCX646MTCX
- Part No.:
- 74LCX646MTCX
- Manufacturer:
- onsemi
- Package:
- 24-TSSOP (0.173", 4.40mm Width)
- Datasheet:
-
74LCX646MTCX.pdf
- Description:
- IC TXRX NON-INVERT 3.6V 24TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,802
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Product details
Overview
74LCX646MTCX from Fairchild Semiconductor is a low-voltage octal transceiver/register IC with 5V-tolerant I/O, designed for bidirectional data flow between 2.5V/3.3V buses and 5V systems. It features registered bus transfer, real-time transparent mode, 7.0 ns max propagation delay at 3.3V, ±24 mA output drive, and power-down high-impedance I/O. It is used in voltage-level bridging applications such as FPGA-to-microcontroller interconnects.
For engineers reviewing the 74LCX646MTCX datasheet, pinout, applications, or equivalent options, key selection criteria include 5V tolerance on all I/O pins, dual-clock register control (CPAB/CPBA), direction-selectable bus transfer (DIR/SAB/SBA), and TSSOP-24 packaging compatible with high-density PCB layouts.
Technical Context
The 74LCX646MTCX implements dual 8-bit registered transceivers with independent clock inputs (CPAB, CPBA) and select controls (SAB, SBA) enabling four bus management modes: real-time A↔B transfer, A-register-to-B, B-register-to-A, and isolated register loading. Its DIR input determines primary data direction when OE is active low.
It operates across 2.3V–3.6V VCC with guaranteed 5V-tolerant I/O, supports live insertion/withdrawal via high-impedance power-up behavior, and integrates patented noise/EMI reduction circuitry. All inputs remain functional during 3-STATE output disable, allowing concurrent data capture and storage.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 2.3V to 3.6V - Enables direct operation from 2.5V or 3.3V logic rails without level shifters. |
| I/O Voltage Tolerance | 0V to 5.5V - Allows safe interfacing with legacy 5V peripherals without external protection. |
| tPD Max | 7.0 ns at VCC = 3.3V - Supports >100 MHz bus timing in transparent mode with margin. |
| Output Drive | ±24 mA at VCC = 3.0V - Drives standard TTL loads and short traces without buffering. |
| ICC Max | 10 µA at VCC = 3.3V - Ensures ultra-low static power in battery-backed or always-on subsystems. |
| Input Leakage | ±5.0 µA - Minimizes signal integrity impact on high-impedance control lines like OE or DIR. |
| Operating Temp | −40°C to +85°C - Qualified for industrial temperature environments without derating. |
Pinout & Package
74LCX646MTCX is packaged in a 24-pin Thin Shrink Small Outline Package (TSSOP), JEDEC MO-153 compliant, 4.4 mm wide, with 0.65 mm lead pitch and exposed pad not present.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A0–A7 | Data Register A Inputs/Outputs | Bidirectional I/O port connected to Register A; latched on CPAB rising edge or passed through in transparent mode. |
| B0–B7 | Data Register B Inputs/Outputs | Bidirectional I/O port connected to Register B; latched on CPBA rising edge or passed through in transparent mode. |
| CPAB | Register A Clock Input | Rising-edge-triggered clock controlling load of A0–A7 into Register A and optional output to B bus. |
| CPBA | Register B Clock Input | Rising-edge-triggered clock controlling load of B0–B7 into Register B and optional output to A bus. |
| SAB | Transmit/Receive Select A→B | When DIR = HIGH and OE = LOW, selects whether A data flows to B in real-time (SAB = LOW) or stored mode (SAB = HIGH). |
| SBA | Transmit/Receive Select B→A | When DIR = LOW and OE = LOW, selects whether B data flows to A in real-time (SBA = LOW) or stored mode (SBA = HIGH). |
| DIR | Direction Control Input | Determines primary bus direction: HIGH enables A→B flow; LOW enables B→A flow when OE is active. |
| OE | Output Enable Input | Active-low control: HIGH forces all I/O into high-impedance state regardless of DIR or clock activity. |
Key Features
| Feature | Design Value |
|---|---|
| 5V-tolerant I/O | Enables seamless integration between 2.5V/3.3V logic domains and 5V peripherals without external clamping diodes or level translators. |
| Dual-register architecture | Allows independent storage and forwarding of data from either bus, supporting time-multiplexed bus arbitration and glitch-free handshaking. |
| Live insertion support | Guaranteed high-impedance I/O during power-up/down eliminates bus contention when hot-plugging modules or daughterboards. |
| Noise/EMI reduction circuitry | Patented internal slew-rate control minimizes simultaneous switching noise, easing EMC compliance in mixed-signal embedded systems. |
| Latch-up immunity | Exceeds 500 mA per JEDEC JESD78, ensuring robustness against transient overvoltage events in noisy industrial environments. |
Applications
| Industrial PLC Backplane Interface | FPGA-to-Microcontroller Bridge |
|---|---|
Use Scenario: Interfacing a 3.3V FPGA I/O bank to a 5V-rated analog I/O module on a modular PLC backplane. IC Role / Device Role / Timing Role: Bidirectional voltage-level translator and register buffer that isolates timing domains while preserving data coherency across clock boundaries. Use Value: Eliminates need for discrete level shifters and external latches; 7.0 ns tPD ensures deterministic setup/hold timing for 100 MHz control cycles. |
Use Scenario: Connecting a 2.5V FPGA configuration interface to a 3.3V ARM Cortex-M7 microcontroller's parallel boot bus. IC Role / Device Role / Timing Role: Registered transceiver synchronizing asynchronous configuration data transfers with local clock domains using CPAB/CPBA edges. Use Value: Prevents metastability during power sequencing; 5V-tolerant I/O tolerates FPGA VCCIO overshoot during reconfiguration. |
| Memory Expansion Subsystem | Legacy Peripheral Adapter |
Use Scenario: Expanding external SRAM capacity on a 3.3V SoC by adding a second 5V-compatible memory bank. IC Role / Device Role / Timing Role: Octal bus transceiver with register hold capability, enabling burst-mode address/data multiplexing between SoC and memory controller. Use Value: ±24 mA drive sustains signal integrity across 10 cm trace lengths; registered mode decouples memory access timing from SoC clock jitter. |
Use Scenario: Adapting a modern 3.3V MCU to legacy 5V parallel printer or display interface. IC Role / Device Role / Timing Role: Direction-controlled bus repeater with real-time and stored transfer modes for handshake protocol emulation (e.g., STROBE/ACK). Use Value: DIR and SAB/SBA inputs allow software-configurable data flow direction and timing alignment without hardware changes. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal transceiver/register applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| 74ALVC164245DGGR | 16-bit, dual-supply (VCCA=2.3–3.6V, VCCB=3.0–5.5V), no internal registers, higher drive (±24 mA), 3.5 ns tPD. | Best for pure level translation without storage; lacks CPAB/CPBA clocked register functionality. | Select when only voltage translation is needed and register staging adds unnecessary latency. |
| SN74LVC8T245PW | 8-bit, single-supply (1.65–5.5V), no internal registers, ±24 mA drive, 3.8 ns tPD, 5V-tolerant inputs only (not outputs). | Requires external pull-ups for 5V output compatibility; no clocked register or stored-mode capability. | Choose for cost-sensitive, non-critical timing applications where register functionality is unused. |
Compared with 74LCX646MTCX, the 74ALVC164245DGGR offers faster speed and wider voltage flexibility but omits register storage, while the SN74LVC8T245PW provides simpler 5V-input-only translation at lower cost but cannot replicate stored-mode bus arbitration or 5V-safe outputs.
Availability
74LCX646MTCX is available at Aetrix Electronics and suitable for industrial PLC backplanes, FPGA-to-MCU bridges, memory expansion subsystems, and legacy peripheral adapters requiring stable component supply and long-term obsolescence management.
Supply support for 74LCX646MTCX 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 power management, analog, and logic ICs before its acquisition by ON Semiconductor in 2016. Its legacy logic families remain widely deployed in industrial and automotive systems.
The LCX family-including the 74LCX646MTCX-was engineered for low-voltage, high-speed bidirectional bus interfacing with 5V tolerance, targeting mixed-voltage system design in telecom infrastructure, industrial controllers, and embedded computing.
FAQ
What is the maximum clock frequency supported by the 74LCX646MTCX?
The 74LCX646MTCX supports a maximum clock frequency of 150 MHz under recommended operating conditions (VCC = 3.3V, CL = 50 pF, TA = −40°C to +85°C). This rating applies to CPAB and CPBA inputs driving register loads. Real-time bus-to-bus transfer operates reliably up to this rate due to its 7.0 ns max propagation delay and tight skew specification (1.0 ns).
Does the 74LCX646MTCX require external pull-up resistors on OE or DIR inputs?
Yes-the 74LCX646MTCX requires a pull-up resistor on OE during power-up/down to ensure high-impedance I/O states, as specified in Note 1 of the datasheet. The minimum resistor value depends on the driver's current-sourcing capability. DIR may be driven directly but must never float; unused DIR or SAB/SBA inputs should be tied HIGH or LOW per recommended operating conditions.
Can the 74LCX646MTCX drive 50 Ω transmission lines directly?
No-the 74LCX646MTCX is not designed for direct 50 Ω line driving. Its AC characteristics (e.g., tPD, skew) are specified with RL = 500 Ω and CL = 30–50 pF. Driving 50 Ω loads would exceed its ±24 mA output rating and distort waveforms. For controlled-impedance routing, use series termination or dedicated line drivers downstream of the 74LCX646MTCX.
Is the 74LCX646MTCX pin-compatible with other LCX-series transceivers like the 74LCX162245?
No-the 74LCX646MTCX is not pin-compatible with the 74LCX162245 or other LCX transceivers. It uses a unique 24-pin TSSOP footprint with dedicated clock (CPAB/CPBA), select (SAB/SBA), and direction (DIR) inputs absent in non-registered devices. Pin mapping differs fundamentally due to its dual-register architecture and control logic.
What is the purpose of the SAB and SBA inputs in the 74LCX646MTCX?
The SAB and SBA inputs configure the 74LCX646MTCX's bus transfer mode when OE is active. SAB controls A→B path behavior (real-time vs. stored), while SBA controls B→A path behavior. Together with DIR, they enable four distinct operational modes: real-time bidirectional pass-through, register-stored forwarding, isolated register loading, and combined clocked+output transfer-all without changing external wiring.
74LCX646MTCX Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Series:
- 74LCX
- Package/Case:
- 24-TSSOP (0.173", 4.40mm 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 ~ 3.6V
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-TSSOP
74LCX646MTCX FAQ
1.How can I place an order for 74LCX646MTCX through Aetrix?
Please submit a Request for Quotation (RFQ) for 74LCX646MTCX 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 74LCX646MTCX reliable?
The price and inventory of 74LCX646MTCX are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 74LCX646MTCX is usually 5 days.
3.What payment methods are accepted for 74LCX646MTCX?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 74LCX646MTCX transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for 74LCX646MTCX?
74LCX646MTCX orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 74LCX646MTCX 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 74LCX646MTCX?
For technical support, including 74LCX646MTCX datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 74LCX646MTCX requirements.
6.How does Aetrix verify that 74LCX646MTCX is sourced from the original manufacturer or authorized distributors?
All 74LCX646MTCX 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 74LCX646MTCX meets industry standards.
7.What is the process for return or replacement of 74LCX646MTCX?
All 74LCX646MTCX units undergo pre-shipment inspection (PSI). If there is an issue with 74LCX646MTCX, 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 74LCX646MTCX part is unused and in its original packaging.
Return procedure for 74LCX646MTCX:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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