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Home > Products > Integrated Circuits (ICs) > Logic > Buffers, Drivers, Receivers, Transceivers

onsemi 74LVTH646WM

Name: 74LVTH646WM
Brand: onsemi
SKU: 74LVTH646WM
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: 74LVTH646WM

Manufacturer:: onsemi

Category:: Buffers, Drivers, Receivers, Transceivers

Package:: 24-SOIC (0.295", 7.50mm Width)

Datasheet:: 74LVTH646WM.pdf

Description:: IC TXRX NON-INVERT 3.6V 24SOP

Quantity:: RFQ Add To RFQ list

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Product details

Overview

74LVTH646WM from Fairchild Semiconductor is a low-voltage octal transceiver/register with 3-STATE outputs, designed for bidirectional data flow between A and B buses in 3.3V systems while maintaining TTL-level interface compatibility with 5V environments. It integrates D-type flip-flops, bushold inputs, and dual-clock control (CPAB/CPBA) to support real-time and registered transfer modes. Key specs include ±32 mA/64 mA drive strength, 150 MHz max clock frequency, and operation across −40°C to +85°C.

For engineers reviewing the 74LVTH646WM datasheet, pinout, applications, or equivalent options, this device enables robust bus isolation, live insertion/extraction, glitch-free power-up/down behavior, and register-controlled data staging in mixed-voltage embedded and industrial control backplanes.

Technical Context

The 74LVTH646WM implements a dual-bus architecture with independent clocking (CPAB for A→B register load, CPBA for B→A), direction control (DIR), and select inputs (SAB/SBA) to configure transparent or stored-mode transfers. Its bushold inputs eliminate external pull-ups, and its BiCMOS process delivers ABT-class speed with LV logic power efficiency.

It supports four fundamental bus-management functions: real-time A↔B transfer, A/B register storage, and simultaneous clocked load + output (e.g., CPAB HIGH + SAB LOW enables A-data load and immediate output to B). Output enable (OE) controls 3-STATE behavior independently of DIR or clock state.

Key Specifications

Parameter	Value and Actual Design Meaning
VCC Range	2.7 V to 3.6 V - Ensures stable operation in 3.3V systems with ±0.3V tolerance margin.
Max Clock Frequency	150 MHz - Supports high-speed synchronous bus handshaking in backplane and memory interface designs.
Output Drive	−32 mA / +64 mA - Enables direct driving of multiple TTL loads without external buffers.
Propagation Delay	1.3 ns (min) to 6.3 ns (max) - Guarantees timing predictability in register-to-bus and clock-to-output paths.
Operating Temperature	−40°C to +85°C - Qualified for industrial-grade thermal environments without derating.
Bushold Input Current	±75 µA at VI = 0.8V/2.0V - Maintains valid logic levels on floating data pins without external biasing.
IOFF Leakage	±100 µA - Prevents current backflow during hot-swap or partial power-down scenarios.

Pinout & Package

74LVTH646WM is housed in a 24-lead SOIC package (JEDEC MS-013, 0.300" wide, Package Number M24B), with gull-wing leads and standard 1.27 mm pitch.

Pin/Terminal	Circuit Role	Design Meaning
A0–A7	Data Register A I/O	Bi-directional bus interface pins for Register A; function as inputs when loading A register, outputs when sourcing A register data to B bus.
B0–B7	Data Register B I/O	Bi-directional bus interface pins for Register B; function as inputs when loading B register, outputs when sourcing B register data to A bus.
CPAB	Register A Clock Input	LOW-to-HIGH transition loads data from A0–A7 into A register and optionally outputs to B bus depending on SAB/DIR/OE.
CPBA	Register B Clock Input	LOW-to-HIGH transition loads data from B0–B7 into B register and optionally outputs to A bus depending on SBA/DIR/OE.
SAB	A-to-B Select Control	When LOW and DIR = LOW, enables real-time A→B transfer; when HIGH, selects A-register-to-B output mode.
SBA	B-to-A Select Control	When LOW and DIR = HIGH, enables real-time B→A transfer; when HIGH, selects B-register-to-A output mode.
DIR	Direction Control	Determines primary bus direction: LOW → A→B path active; HIGH → B→A path active; does not disable register clocks.
OE	Output Enable	HIGH disables all A/B outputs (3-STATE); LOW enables outputs per DIR/SAB/SBA configuration - input functions remain active regardless.

Key Features

Feature	Design Value
Bushold Inputs	Eliminates need for external pull-up resistors on A0–A7 and B0–B7, reducing BOM count and PCB space in sparse-bus configurations.
Live Insertion/Extraction	Power-up/down high-impedance behavior prevents bus contention during hot-plug operations in modular backplane systems.
Mixed-Voltage Interface	Accepts 5.5V-tolerant inputs and drives 5V TTL loads while operating from 3.3V supply - bridges legacy and modern voltage domains.
Registered + Transparent Modes	Supports both clock-synchronized data staging (via CPAB/CPBA) and immediate pass-through (SAB/SBA-controlled), enabling flexible bus arbitration schemes.
High Sink/Source Drive	64 mA sink capability allows direct termination of unterminated stubs or fan-out to ≥10 LSTTL loads without buffering.

Applications

Industrial Backplane Data Routing	Memory Expansion Interface
Use Scenario: Isolating and synchronizing data between CPU and peripheral modules across a 24-bit parallel backplane with mixed 3.3V/5V subsystems. IC Role / Device Role / Timing Role: Bidirectional transceiver and register staging element that buffers and clocks address/data between master and slave slots using CPAB/CPBA-triggered latching. Use Value: Enables deterministic timing alignment across variable-length traces and eliminates bus contention during module insertion/removal via OE-controlled 3-STATE isolation.	Use Scenario: Extending SRAM or Flash memory width in an FPGA-based controller by multiplexing two 8-bit memory banks onto a shared 16-bit data bus. IC Role / Device Role / Timing Role: Octal register/transceiver managing data flow direction and timing between FPGA I/O and memory banks, synchronized to FPGA clock domain. Use Value: Reduces FPGA pin count by half while preserving full bandwidth through registered read/write staging and bushold-enabled idle-state stability.
Hot-Swappable I/O Module	Legacy System Voltage Translation
Use Scenario: Supporting field-replaceable I/O cards in programmable logic controllers where modules may be inserted or removed under power. IC Role / Device Role / Timing Role: Bus interface IC providing glitch-free power-up/down behavior and real-time data pass-through or register hold during card reconfiguration. Use Value: Prevents system lockup or data corruption during hot-swap events via inherent high-impedance default state and bushold input retention.	Use Scenario: Interfacing a 3.3V microcontroller to legacy 5V peripherals such as UART transceivers, display drivers, or sensor signal conditioners. IC Role / Device Role / Timing Role: Level-shifting transceiver with register capability, translating logic levels while supporting both immediate and clocked data transfer protocols. Use Value: Eliminates discrete level-shifters and pull-up networks, simplifying design and improving noise immunity with controlled edge rates and 5.5V-tolerant inputs.

Industrial Backplane Data Routing

Memory Expansion Interface

Use Scenario: Isolating and synchronizing data between CPU and peripheral modules across a 24-bit parallel backplane with mixed 3.3V/5V subsystems.

IC Role / Device Role / Timing Role: Bidirectional transceiver and register staging element that buffers and clocks address/data between master and slave slots using CPAB/CPBA-triggered latching.

Use Value: Enables deterministic timing alignment across variable-length traces and eliminates bus contention during module insertion/removal via OE-controlled 3-STATE isolation.

Use Scenario: Extending SRAM or Flash memory width in an FPGA-based controller by multiplexing two 8-bit memory banks onto a shared 16-bit data bus.

IC Role / Device Role / Timing Role: Octal register/transceiver managing data flow direction and timing between FPGA I/O and memory banks, synchronized to FPGA clock domain.

Use Value: Reduces FPGA pin count by half while preserving full bandwidth through registered read/write staging and bushold-enabled idle-state stability.

Hot-Swappable I/O Module

Legacy System Voltage Translation

Use Scenario: Supporting field-replaceable I/O cards in programmable logic controllers where modules may be inserted or removed under power.

IC Role / Device Role / Timing Role: Bus interface IC providing glitch-free power-up/down behavior and real-time data pass-through or register hold during card reconfiguration.

Use Value: Prevents system lockup or data corruption during hot-swap events via inherent high-impedance default state and bushold input retention.

Use Scenario: Interfacing a 3.3V microcontroller to legacy 5V peripherals such as UART transceivers, display drivers, or sensor signal conditioners.

IC Role / Device Role / Timing Role: Level-shifting transceiver with register capability, translating logic levels while supporting both immediate and clocked data transfer protocols.

Use Value: Eliminates discrete level-shifters and pull-up networks, simplifying design and improving noise immunity with controlled edge rates and 5.5V-tolerant inputs.

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal transceiver/register applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
SN74LVT646PWR	TI part uses different BiCMOS process; slightly higher ICCZ (0.35 mA vs. 0.19 mA) and lower VOL at 64 mA (0.5 V vs. 0.55 V).	Same 24-pin TSSOP footprint but not pin-compatible with 74LVTH646WM's SOIC layout; requires PCB redesign.	Select when TSSOP packaging and TI supply chain alignment are prioritized over drop-in replacement.
74ALVCH16646DLR	16-bit variant with different pinout and dual-supply (1.65–3.6V) support; lacks bushold and has no 5V-tolerant inputs.	Designed for wider buses and lower VCC operation; unsuitable for 5V interface or hot-swap use cases requiring bushold.	Choose only for new 16-bit, single-supply designs where extended voltage range outweighs interface compatibility needs.

Compared with SN74LVT646PWR and 74ALVCH16646DLR, the 74LVTH646WM uniquely combines 5V-tolerant inputs, bushold, SOIC packaging, and proven industrial temperature reliability - making it optimal for retrofitting 3.3V/5V mixed-signal backplanes without layout changes.

Availability

74LVTH646WM is available at Aetrix Electronics and suitable for industrial backplane routing, memory expansion interfaces, hot-swappable I/O modules, and legacy system voltage translation requiring stable component supply and long-term lifecycle support.

Supply support for 74LVTH646WM 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 analog and power IC manufacturer, acquired by ON Semiconductor in 2016; its legacy logic portfolio remains widely deployed in industrial and telecom infrastructure.

The 74LVTH646WM belongs to Fairchild's LVTH (Low-Voltage Transistor-Transistor Logic with Bushold) family, engineered for high-speed, low-power 3.3V bus interfacing with backward compatibility to 5V TTL systems.

FAQ

What is the maximum clock frequency supported by the 74LVTH646WM?

The 74LVTH646WM supports a maximum clock frequency of 150 MHz under recommended operating conditions (VCC = 3.3 V ± 0.3 V, TA = −40°C to +85°C). This rating applies to both CPAB and CPBA inputs and is guaranteed across the full industrial temperature range, enabling use in high-speed synchronous bus architectures without timing margin compromise.

Does the 74LVTH646WM require external pull-up resistors on its data inputs?

No, the 74LVTH646WM features bushold circuitry on all A0–A7 and B0–B7 inputs, which actively maintains the last-valid logic state without external biasing. This eliminates the need for pull-up resistors, reduces component count, and improves reliability in sparsely populated or floating-bus scenarios - a key advantage confirmed in the device's Functional Description and DC Electrical Characteristics tables.

Can the 74LVTH646WM interface directly with 5V logic systems?

Yes, the 74LVTH646WM accepts input voltages up to 5.5 V and provides TTL-compatible output levels, allowing direct connection to 5V systems while operating from a 3.3V supply. Its 5V-tolerant inputs and −32 mA/+64 mA drive strength ensure interoperability with legacy 5V peripherals without level-shifting circuitry - explicitly stated in the General Description and Absolute Maximum Ratings sections.

What is the operating temperature range for the 74LVTH646WM?

The 74LVTH646WM is rated for free-air operating temperatures from −40°C to +85°C, qualifying it for industrial-grade applications. This range is specified in the Recommended Operating Conditions table and validated across all electrical parameters including propagation delay, output voltage, and leakage current - ensuring reliable performance in harsh thermal environments.

Is the 74LVTH646WM suitable for hot-swap applications?

Yes, the 74LVTH646WM supports live insertion and extraction due to its power-up/power-down high-impedance feature and bushold inputs. During power transitions, outputs enter a high-impedance state before supply stabilization, preventing bus contention - a capability documented in the Features list and verified in the Power Up/Down 3-STATE Output Current specification (IPU/PD = ±100 µA).

74LVTH646WM Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: 74LVTH

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:: 32mA, 64mA

Voltage - Supply:: 2.7V ~ 3.6V

Operating Temperature:: -40°C ~ 85°C (TA)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 24-SOP

74LVTH646WM FAQ

1.How can I place an order for 74LVTH646WM through Aetrix?

Please submit a Request for Quotation (RFQ) for 74LVTH646WM 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 74LVTH646WM reliable?

The price and inventory of 74LVTH646WM are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for 74LVTH646WM is usually 5 days.

3.What payment methods are accepted for 74LVTH646WM?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for 74LVTH646WM transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for 74LVTH646WM?

74LVTH646WM orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your 74LVTH646WM 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 74LVTH646WM?

For technical support, including 74LVTH646WM datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your 74LVTH646WM requirements.

6.How does Aetrix verify that 74LVTH646WM is sourced from the original manufacturer or authorized distributors?

All 74LVTH646WM 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 74LVTH646WM meets industry standards.

7.What is the process for return or replacement of 74LVTH646WM?

All 74LVTH646WM units undergo pre-shipment inspection (PSI). If there is an issue with 74LVTH646WM, 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 74LVTH646WM part is unused and in its original packaging.

Return procedure for 74LVTH646WM:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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