NXP Semiconductors 74HC640DB,118

Overview

74HC640DB,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 9 ns at VCC = 5 V, 3.5 pF input capacitance, and operates across −40 °C to +125 °C - used in industrial backplane interface and legacy TTL-compatible system upgrades.

For engineers reviewing the 74HC640DB,118 datasheet, 74HC640DB,118 pinout, 74HC640DB,118 application, or 74HC640DB,118 equivalent, key selection criteria include verified 3-state timing (tPZH/tPHZ ≤ 45 ns), inverting logic behavior, SO20 package compatibility, and direct LSTTL-level interoperability without level-shifting.

Technical Context

The 74HC640DB,118 implements dual-directional inverting data transfer using complementary CMOS logic, where DIR selects signal path (A→B or B→A) and OE places all outputs in high-impedance state. Its architecture supports cascading via shared OE/DIR lines and isolates buses during idle cycles.

It complies with JEDEC standard No. 7A and matches LSTTL pinout and voltage thresholds (HCT variant supports TTL-compatible inputs). Propagation delays are symmetric for both directions (An↔Bn), and output transition times remain under 18 ns at 5 V, enabling reliable operation in synchronous bus arbitration systems.

Key Specifications

Pinout & Package

74HC640DB,118 is housed in a 20-pin small-outline (SO) package (SO20), 7.5 mm body width, 1.27 mm pitch, with gull-wing leads and moisture sensitivity level MSL3. 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 74HCT640DB,118 and SN74LVTH16245DGGR, the 74HC640DB,118 provides optimal balance of voltage flexibility (2–6 V), proven industrial temperature support, and exact 74LS640 pinout - making it the preferred choice for retrofitting and mixed-supply embedded systems.

Availability

74HC640DB,118 is available at Aetrix Electronics and suitable for industrial backplane interface, legacy system bus extension, and automotive ECU data multiplexing requiring stable component supply and long-term lifecycle assurance.

Supply support for 74HC640DB,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 logic, analog, and discrete components - spun off from Philips Semiconductors in 2017 with full IP and manufacturing continuity.

The 74HC640DB,118 belongs to Nexperia's 74HC logic family, engineered for robustness in industrial and automotive applications where pin compatibility, wide supply range, and extended temperature operation are essential design requirements.

FAQ

What is the maximum clock frequency supported by the 74HC640DB,118 in a bidirectional bus application?

The 74HC640DB,118 does not operate on a clock signal - it is an asynchronous transceiver. Its usable data rate depends on propagation delay (9 ns typical) and system timing margins. For reliable operation with 15 pF load, maximum toggle rate is approximately 35 MHz in point-to-point configurations. The 74HC640DB,118 must be synchronized externally via DIR and OE control signals aligned to system timing constraints.

Does the 74HC640DB,118 support 3.3 V operation, and what are the implications for input thresholds?

Yes, the 74HC640DB,118 supports 3.3 V operation within its 2.0 V–6.0 V VCC range. At 3.3 V, input thresholds are CMOS-compatible (VIH ≈ 2.1 V, VIL ≈ 1.2 V), requiring compatible 3.3 V logic drivers. Unlike the HCT variant, the 74HC640DB,118 does not guarantee TTL-level input recognition at 3.3 V - use 74HCT640DB,118 if interfacing with legacy 5 V TTL sources.

How does the inverting behavior of the 74HC640DB,118 affect system-level data integrity?

The 74HC640DB,118 inverts data on both A→B and B→A paths - meaning two passes restore original polarity. This behavior simplifies designs where bus polarity must match legacy hardware (e.g., certain memory controllers). System-level integrity is preserved because inversion is deterministic and symmetrical; no additional logic is needed to compensate, and timing remains consistent across directions.

Can the 74HC640DB,118 replace a 74LS640 in an existing PCB layout without modifications?

Yes - the 74HC640DB,118 is pin-compatible with 74LS640 and uses the same SO20 footprint. However, verify that the board's VCC rail is regulated to 4.5–5.5 V and that decoupling capacitors (≥100 nF per VCC pin) are present. The 74HC640DB,118 draws significantly less quiescent current, reducing thermal load but requiring attention to unused input termination to prevent floating nodes.

What is the recommended PCB layout practice for minimizing noise coupling on the DIR and OE control lines of the 74HC640DB,118?

Route DIR and OE as short, direct traces adjacent to GND planes; avoid crossing noisy clocks or switching power lines. Use series 33 Ω resistors near the 74HC640DB,118 inputs to dampen ringing, and tie unused inputs (if any) to VCC or GND with 10 kΩ resistors. Ensure local 100 nF ceramic decoupling between VCC and GND pins 10 and 20, placed within 3 mm of the 74HC640DB,118 body.