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STMicroelectronics 74LCX646TTR
- Part No.:
- 74LCX646TTR
- Manufacturer:
- STMicroelectronics
- Package:
- 24-TSSOP (0.173", 4.40mm Width)
- Datasheet:
-
74LCX646TTR.pdf
- Description:
- IC TXRX NON-INVERT 3.6V 24TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:2,743
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Product details
Overview
74LCX646TTR from STMicroelectronics is a low-voltage CMOS octal bus transceiver and register with 3-state outputs, 5V-tolerant I/O, 7.0 ns max propagation delay at 3V, ±24 mA output drive, and 2.0–3.6 V operating range. It functions as a bidirectional data multiplexer/register in 3.3V PCI-bus and mixed-voltage system interfaces.
For engineers reviewing the 74LCX646TTR datasheet, 74LCX646TTR pinout, 74LCX646TTR application, or 74LCX646TTR equivalent, key selection criteria include 5V-tolerant I/O compatibility, clocked register storage (CAB/CBA edge-triggered), DIR/G-controlled direction/enable logic, and TSSOP-24 package suitability for high-density PCB layouts.
Technical Context
The 74LCX646TTR integrates dual 8-bit transceivers with independent A↔B direction control, two edge-triggered D-type registers (clocked on CAB and CBA rising edges), and multiplexed select logic (SAB/SBA) enabling transparent or registered data routing. Its symmetrical 24 mA |IOH|/IOL drive supports PCI bus signaling levels.
It operates within 2.0–3.6 V VCC while accepting 0–5.5 V inputs and driving 0–5.5 V outputs, with power-down input/output protection and latch-up immunity >500 mA per JESD17. Propagation delays are balanced (tPLH ≅ tPHL), and skew is guaranteed ≤1.0 ns across outputs.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage Range | 2.0 V to 3.6 V - Enables direct integration into 3.3 V systems with 1.5 V data retention during sleep. |
| Max Propagation Delay | 7.0 ns at VCC = 3.0–3.6 V - Supports ≥150 MHz clock operation in registered mode with timing margin. |
| Output Drive Strength | ±24 mA at VCC = 3.0–3.6 V - Meets PCI bus loading requirements and drives multiple TTL loads. |
| I/O Voltage Tolerance | 0–5.5 V input/output - Allows safe interfacing between 3.3 V logic and legacy 5 V subsystems without level shifters. |
| Input Capacitance | 6 pF - Minimizes capacitive loading on upstream drivers, preserving signal integrity in high-speed buses. |
| Power Dissipation Cap | 37 pF - Enables accurate dynamic current estimation (ICC(opr) = CPD × VCC × fIN + ICC/8) for thermal design. |
Pinout & Package
TSSOP-24 package: 7.7 mm × 4.4 mm body, 0.65 mm pitch, 1.1 mm height, lead-free and RoHS-compliant.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (CAB) | A-to-B Clock Input | Rising-edge triggered; latches A-bus data into internal register for B-bus output or storage. |
| 2 (SAB) | Select A-to-B Source | Chooses between real-time A-bus (transparent) or registered A-data for B-bus output. |
| 3 (DIR) | Direction Control | High = A→B data flow; Low = B→A data flow when G is active (low). |
| 4–11 (A1–A8) | A-Bus I/O Terminals | Bidirectional 3-state ports; function as inputs (when driven by B) or outputs (when driving B) depending on DIR/G. |
| 12 (GND) | Ground Reference | Common return path for all internal logic and I/O circuits; decoupling capacitor placement critical near this pin. |
| 13–20 (B1–B8) | B-Bus I/O Terminals | Bidirectional 3-state ports mirroring A-bus behavior; support simultaneous register storage and bus driving. |
| 21 (G) | Output Enable (Active LOW) | When HIGH, forces all A/B outputs to high-impedance; enables isolation while preserving input functionality. |
| 22 (SBA) | Select B-to-A Source | Chooses between real-time B-bus or registered B-data for A-bus output. |
| 23 (CBA) | B-to-A Clock Input | Rising-edge triggered; latches B-bus data into internal register for A-bus output or storage. |
| 24 (VCC) | Positive Supply | Supplies core logic and I/O buffers; requires local 0.1 µF ceramic decoupling adjacent to pin. |
Key Features
| Feature | Design Value |
|---|---|
| 5V-tolerant I/O | Supports mixed-voltage board design without external level translators; simplifies migration from 5V to 3.3V systems. |
| Dual clocked registers | Independent CAB and CBA inputs enable asynchronous capture of A- and B-bus data, enabling ping-pong buffering. |
| Symmetrical 24 mA drive | Ensures matched rise/fall times and reduced ground bounce in high-speed bus switching applications. |
| Power-down protection | Prevents back-driving and leakage when VCC = 0 V, protecting connected devices during hot-swap or partial power-down. |
| Latch-up immunity >500 mA | Guarantees robust operation in noisy industrial environments per JESD17, eliminating need for external current limiting. |
Applications
| PCI Bus Interface | 3.3V/5V Mixed-Voltage Bridge |
|---|---|
|
Use Scenario: Interfacing a 3.3 V microcontroller bus to a legacy 5 V PCI peripheral slot. IC Role / Device Role / Timing Role: Bidirectional voltage-tolerant transceiver with registered data staging to meet PCI setup/hold timing. Use Value: Eliminates discrete level shifters while maintaining 150 MHz clock compatibility and meeting PCI electrical specs at 24 mA drive. |
Use Scenario: Isolating and synchronizing data between 5 V sensor front-end and 3.3 V FPGA processing unit. IC Role / Device Role / Timing Role: Direction-controlled bus buffer with clocked register staging to decouple timing domains. Use Value: Enables deterministic data capture via CAB/CBA clocks and glitch-free handoff using SAB/SBA multiplexing. |
| Hot-Swappable Backplane Module | Low-Power Industrial Controller Bus |
|
Use Scenario: Hot-plug capable module interface where VCC may be absent during insertion. IC Role / Device Role / Timing Role: Isolation element with power-down protected I/O preventing backfeed into unpowered modules. Use Value: Complies with hot-swap safety requirements via zero-current I/O leakage (<10 µA) when VCC = 0 V. |
Use Scenario: Local I/O expansion bus in battery-powered PLC with strict quiescent current budget. IC Role / Device Role / Timing Role: Low-voltage transceiver minimizing ICC(opr) via 37 pF CPD and 10 µA ICC(quiescent). Use Value: Achieves <1 µA/MHz dynamic current consumption at 3.3 V, extending operational runtime without sacrificing speed. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal transceiver/register applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| 74ALVC16646DL | 16-bit (dual-octal), higher drive (±24 mA), but no 5V tolerance on inputs; requires external clamping for 5V signals. | Best suited for pure 3.3 V systems needing wider bus width; unsuitable for direct 5V interface without redesign. | Select when board-level voltage translation is already implemented and 16-bit width is required. |
| SN74LVC8T245RHLR | 8-bit, 5V-tolerant, but lacks internal registers and clocked storage; only transparent transceiver mode. | Applicable where real-time pass-through suffices; cannot replace registered data staging or ping-pong buffering. | Select when clocked register functionality is unnecessary and lower pin count (20-pin VQFN) is prioritized. |
Compared with 74LCX646TTR, the 74ALVC16646DL offers double bus width but forfeits 5V I/O safety, while SN74LVC8T245RHLR reduces footprint and cost but eliminates clocked register capability essential for timing-critical buffering.
Availability
74LCX646TTR is available at Aetrix Electronics and suitable for PCI bus interfaces, 3.3V/5V mixed-voltage bridges, and hot-swappable backplane modules requiring stable component supply and long-term lifecycle assurance.
Supply support for 74LCX646TTR 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
STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing analog, digital, and mixed-signal ICs for automotive, industrial, and consumer markets.
The M74LCX series targets low-voltage, high-speed logic applications requiring 5V-tolerant I/O and sub-10 ns performance at 3.3 V, specifically addressing PCI, memory interface, and mixed-supply system needs.
FAQ
Can 74LCX646TTR operate with VCC = 2.5 V while maintaining full 5V input tolerance?
Yes. Per Table 5, VI is specified 0–5.5 V across the full recommended VCC range (2.0–3.6 V). At VCC = 2.5 V, inputs remain 5V-tolerant, and DC specs (VIH/VIL, IOH/IOL) are guaranteed per Table 6, enabling robust mixed-voltage operation without derating.
What is the functional difference between SAB/SBA and DIR pins?
DIR controls real-time data direction (A→B or B→A) when G is active; SAB/SBA select source for registered output - SAB chooses between live A-bus or A-register data for B-bus output, while SBA does the same for B-register → A-bus. They operate independently to enable flexible data routing.
Does the 74LCX646TTR support hot-plug operation when VCC is ramping?
Yes. Power-down protection ensures inputs and outputs remain high-impedance and non-destructive when VCC = 0 V. The device draws <10 µA Ioff (Table 6) with VI or VO = 5.5 V, preventing back-current injection into unpowered systems during insertion.
How does the 74LCX646TTR achieve balanced tPLH/tPHL despite process variation?
It uses matched P- and N-channel transistor sizing in its output stage and symmetric layout topology, as confirmed by balanced propagation delay specs (tPLH ≅ tPHL ≤7.0 ns) and skew ≤1.0 ns (Table 8). This matching is process-verified and guaranteed over temperature and voltage.
74LCX646TTR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- STMicroelectronics
- 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:
- -55°C ~ 125°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 24-TSSOP
74LCX646TTR FAQ
1.How can I place an order for 74LCX646TTR through Aetrix?
Please submit a Request for Quotation (RFQ) for 74LCX646TTR 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 74LCX646TTR reliable?
The price and inventory of 74LCX646TTR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 74LCX646TTR is usually 5 days.
3.What payment methods are accepted for 74LCX646TTR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 74LCX646TTR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for 74LCX646TTR?
74LCX646TTR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your 74LCX646TTR 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 74LCX646TTR?
For technical support, including 74LCX646TTR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 74LCX646TTR requirements.
6.How does Aetrix verify that 74LCX646TTR is sourced from the original manufacturer or authorized distributors?
All 74LCX646TTR 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 74LCX646TTR meets industry standards.
7.What is the process for return or replacement of 74LCX646TTR?
All 74LCX646TTR units undergo pre-shipment inspection (PSI). If there is an issue with 74LCX646TTR, 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 74LCX646TTR part is unused and in its original packaging.
Return procedure for 74LCX646TTR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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