NXP Semiconductors 74HCT640DB,118

Overview

74HCT640DB,118 from Nexperia (formerly Philips Semiconductors) is an octal inverting bus transceiver with 3-state outputs, designed for bidirectional data flow control between two 8-bit buses. It features direction control (DIR), active-low output enable (OE), propagation delay of 11 ns at VCC = 4.5 V, and operates over −40 °C to +85 °C. It is used in legacy industrial backplane interfaces requiring level-shifted TTL-compatible signaling.

For engineers reviewing the 74HCT640DB,118 datasheet, 74HCT640DB,118 pinout, 74HCT640DB,118 application, or 74HCT640DB,118 equivalent, key selection criteria include its inverting logic behavior, 3-state isolation timing (tPZH/tPHZ ≤ 45 ns), bus driver output capability, and compatibility with LSTTL input thresholds at 5 V supply.

Technical Context

The 74HCT640DB,118 implements dual-directional data transfer using a single DIR input to select A→B (DIR = LOW) or B→A (DIR = HIGH), with all outputs inverted relative to inputs. Its HCT logic family ensures TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) while driving CMOS loads.

Output enable (OE) asserts high-impedance state on both A and B ports simultaneously, enabling bus sharing without contention. Propagation delays are symmetric for both directions (An↔Bn), and transition times remain under 18 ns, supporting reliable operation in synchronous 8-bit data paths up to ~20 MHz.

Key Specifications

Pinout & Package

74HCT640DB,118 is housed in a 20-pin SO20 (Small Outline) package per JEDEC MS-013, with 0.65 mm pitch and body width of 7.5 mm. Pin 1 is marked by a bevelled corner or notch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT245N and 74HCT640D,623, the 74HCT640DB,118 provides guaranteed inverting behavior in a tube-packaged SO20 variant-critical for drop-in replacement in legacy designs where polarity matching and manual assembly are mandatory.

Availability

74HCT640DB,118 is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy microprocessor bus extensions, and automated manufacturing fixture control requiring stable component supply and long-term obsolescence management.

Supply support for 74HCT640DB,118 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

Nexperia is a global semiconductor expert delivering high-performance, reliable discrete, logic, and MOSFET solutions with focus on efficiency and sustainability.

The 74HCT640DB,118 belongs to Nexperia's legacy HC/HCT logic portfolio, engineered specifically for robust interoperability with TTL-based systems in industrial and instrumentation applications.

FAQ

What logic family does the 74HCT640DB,118 belong to, and why does it matter for system integration?

The 74HCT640DB,118 belongs to the 74HCT (High-speed CMOS with TTL-compatible inputs) logic family. This means it accepts standard TTL voltage thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) while delivering CMOS-level noise immunity and low power consumption. For system integration, this eliminates level shifters when connecting to legacy 74LS or microcontroller GPIOs, simplifying board design and improving signal integrity in mixed-technology environments where the 74HCT640DB,118 serves as a bus bridge.

Does the 74HCT640DB,118 support bidirectional data flow without external control logic?

Yes-the 74HCT640DB,118 supports full bidirectional data flow using only two control inputs: DIR (direction) and OE (output enable). When OE is LOW, DIR = LOW routes inverted data from A0–A7 to B0–B7; DIR = HIGH routes inverted data from B0–B7 to A0–A7. No external gates or latches are needed, making the 74HCT640DB,118 ideal for compact bus arbitration schemes where space and component count are constrained.

What is the significance of the "DB" suffix in 74HCT640DB,118?

The "DB" suffix in 74HCT640DB,118 denotes the SO20 (Small Outline) package type per Nexperia's ordering convention-specifically a 20-pin plastic small-outline integrated circuit with 0.65 mm lead pitch. The "118" indicates tube packaging (non-tape-and-reel), distinguishing it from tape-and-reel variants like "623". This matters for assembly planning: the 74HCT640DB,118 is intended for manual or semi-automated insertion, not high-speed pick-and-place feeders.

Can the 74HCT640DB,118 replace a 74LS640 in an existing design?

Yes-the 74HCT640DB,118 is pin-compatible and functionally equivalent to the 74LS640, with identical pinout, inverting 3-state behavior, and DIR/OE control. Its TTL-compatible inputs ensure direct substitution without circuit modification. However, the 74HCT640DB,118 draws significantly less quiescent current and offers better noise margins, making it a recommended upgrade where reliability and power efficiency are priorities in the same physical layout.

What thermal considerations apply to the 74HCT640DB,118 in continuous bus-driving operation?

The 74HCT640DB,118 has a maximum junction temperature of +125 °C and thermal resistance θJA ≈ 110 K/W in SO20 package. Under worst-case conditions (all 16 outputs driving 6 mA into 50 pF loads at 20 MHz), power dissipation remains below 100 mW-well within safe limits without heatsinking. Still, maintaining adequate copper pour on VCC/GND planes and avoiding enclosure stacking ensures the 74HCT640DB,118 sustains −40 °C to +85 °C operation across full industrial duty cycles.