NXP Semiconductors 74LVT646D,112

Overview

74LVT646D,112 from NXP Semiconductors (formerly Philips) is a 3.3V octal bus transceiver/register with 3-State outputs, combining bidirectional data transfer and independent A/B register storage in a single 24-pin SO package. It supports real-time and stored data multiplexing, delivers ±32mA/±64mA output drive, and interfaces directly with 5V TTL systems while operating at 3.3V VCC.

For engineers reviewing the 74LVT646D,112 datasheet, 74LVT646D,112 pinout, 74LVT646D,112 application, or 74LVT646D,112 equivalent, key selection criteria include its dual-register architecture, bus-hold inputs eliminating external pull-ups, power-up 3-State behavior, and compatibility with mixed-voltage backplane and memory interface designs.

Technical Context

The 74LVT646D,112 integrates transceiver logic and D-type flip-flops to enable four distinct bus management modes: real-time A↔B transfer, isolated A→B or B→A storage, and concurrent register loading. Its DIR and OE pins control direction and output state independently, while CPAB/CPBA and SAB/SBA pins govern clocked register capture and multiplexed output sourcing.

It uses BiCMOS process technology for high-speed operation (150 MHz max clock frequency at 3.3V), low propagation delay (2.7–2.8 ns typical An↔Bn), and robust DC characteristics including bus-hold current (±75 µA), latch-up immunity (>500 mA), and ESD protection (>2000 V HBM). Input thresholds are TTL-compatible (VIL = 0.8 V, VIH = 2.0 V), enabling direct interfacing with legacy 5V logic.

Key Specifications

Pinout & Package

74LVT646D,112 is housed in a 24-pin plastic small outline (SO) package (SOT163-1), 7.5 mm body width, surface-mount compatible with standard reflow profiles.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC646APW and 74ALVT646D,112, the 74LVT646D,112 uniquely balances 5V-tolerant interfacing, moderate speed (150 MHz), and ultra-low standby current (0.13 mA), making it optimal for cost-sensitive, mixed-voltage industrial backplane applications where robustness and compatibility outweigh peak performance needs.

Availability

74LVT646D,112 is available at Aetrix Electronics and suitable for backplane interface, memory subsystem bridging, hot-swappable module hubs, and mixed-voltage test fixtures requiring stable component supply across extended production lifecycles.

Supply support for 74LVT646D,112 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

NXP Semiconductors, formerly Philips Semiconductors, is a global leader in high-performance analog and logic ICs, with core expertise in automotive, industrial, and communication semiconductor solutions.

The 74LVT646D,112 belongs to NXP's LVT (Low-Voltage TTL) logic family, designed specifically for reliable 3.3V operation with backward compatibility to 5V TTL systems in demanding industrial and telecom infrastructure applications.

FAQ

What is the maximum clock frequency supported by the 74LVT646D,112?

The 74LVT646D,112 supports a maximum clock frequency of 150 MHz when operated at VCC = 3.3 V ± 0.3 V over the full temperature range (–40°C to +85°C). This specification is verified under AC test conditions with CL = 50 pF and tR/tF = 2.5 ns. At VCC = 2.7 V, the maximum clock frequency drops to 120 MHz. The 74LVT646D,112 achieves this performance using BiCMOS process technology, enabling high-speed register capture without compromising noise immunity or power efficiency.

Does the 74LVT646D,112 support 5V-tolerant inputs and outputs?

Yes, the 74LVT646D,112 supports 5V-tolerant inputs and outputs while operating from a 3.3V supply. Its VI and VOUT ratings extend to 5.5 V and 7.0 V respectively, allowing direct connection to 5V TTL buses without external level-shifting components. Input thresholds (VIH = 2.0 V, VIL = 0.8 V) match standard TTL logic levels, and output drive capability (+64 mA/–32 mA) ensures compatibility with legacy 5V loads. This feature is integral to the 74LVT646D,112's role in mixed-voltage system integration.

How does the bus-hold function work on the 74LVT646D,112?

The 74LVT646D,112 implements bus-hold circuitry exclusively on the A-side inputs (A0–A7), providing ±75 µA overdrive current to maintain valid logic states on floating pins. This eliminates the need for external pull-up resistors in unconnected or sparsely populated configurations. Bus-hold is inactive on B-side pins and does not affect output drivers or register functionality. The 74LVT646D,112's bus-hold behavior is specified at VCC = 3 V and is fully operational across the rated temperature range.

What happens to the outputs of the 74LVT646D,112 during power-up?

During power-up, the 74LVT646D,112 enters a defined 3-State (high-impedance) condition on all outputs, preventing bus contention before control signals (OE, DIR) stabilize. This power-up 3-State behavior is guaranteed across the full VCC ramp rate (up to 100 µs transition from 1.2 V to 3.3 V) and is independent of input pin states. The 74LVT646D,112 also features power-up reset, ensuring internal registers initialize to a known state, further enhancing system reliability at startup.

Can the 74LVT646D,112 perform simultaneous register loading and real-time data transfer?

Yes, the 74LVT646D,112 supports concurrent register loading and real-time data transfer. When OE is low and DIR is asserted, data flows in real time between A and B buses, while independent CPAB/CPBA edges simultaneously clock data into the respective A or B registers. This dual-mode operation enables applications such as pipeline staging, where incoming data is both forwarded and captured for later use. The 74LVT646D,112's architecture explicitly permits this behavior, as confirmed in its function table and logic diagram.