Texas Instruments CD74HCT640EE4

Overview

CD74HCT640EE4 from Texas Instruments is an inverting octal three-state bus transceiver designed for bidirectional asynchronous data transfer between parallel buses in industrial and military-grade systems. It operates at 4.5 V to 5.5 V, supports -55°C to +125°C temperature range, delivers 6 mA output drive, and features buffered inputs with TTL-compatible logic thresholds (VIL = 0.8 V max, VIH = 2 V min).

For engineers reviewing the CD74HCT640EE4 datasheet, CD74HCT640EE4 pinout, CD74HCT640EE4 application, or CD74HCT640EE4 equivalent, key selection factors include its 3-state control architecture (DIR/OE), propagation delay of 22–33 ns at 5 V, LSTTL load compatibility (15 loads), and PDIP-20 packaging for through-hole reliability in harsh environments.

Technical Context

The CD74HCT640EE4 implements a dual-bus interface using complementary CMOS circuitry with inverting data paths on both A→B and B→A directions. Its DIR input selects direction while OE enables/disables all outputs into high-impedance state-enabling time-multiplexed bus sharing without contention.

It uses silicon-gate CMOS technology to achieve TTL-level input compatibility and low quiescent current (ICC ≤ 160 µA over full temperature range), while maintaining balanced propagation delays (tpd ≤ 33 ns) and fast transition times (tt ≤ 15 ns) under 50 pF load conditions.

Key Specifications

Pinout & Package

CD74HCT640EE4 is packaged in a 20-pin plastic dual in-line package (PDIP-N), with 25.40 mm × 6.35 mm body size and through-hole mounting. Pin 1 is marked by a notch or dot; the package is RoHS-compliant with NiPdAu lead finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT245N and CD74HC640E, the CD74HCT640EE4 uniquely provides inverting functionality with guaranteed TTL input compatibility and military-grade temperature support-making it optimal for legacy 5 V bus architectures requiring strict signal inversion and rugged environmental performance.

Availability

CD74HCT640EE4 is available at Aetrix Electronics and suitable for industrial PLC backplanes, military data link interfaces, and automotive engine control units requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HCT640EE4 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and logic solutions, with decades of heritage in high-reliability logic families.

The CD74HCT640EE4 belongs to TI's CD74HCT high-speed CMOS logic series, engineered for seamless integration into 5 V TTL-compatible digital systems demanding robustness, low power, and wide temperature operation.

FAQ

What is the maximum clock frequency supported by CD74HCT640EE4 in a data bus application?

The CD74HCT640EE4 does not operate on a clock signal-it is a combinational transceiver. Its usable data rate depends on propagation delay (33 ns max) and bus loading. For clean 8-bit parallel transfers, it reliably supports sustained bus cycles up to ~20 MHz in typical PCB layouts with 50 pF load per line. System-level timing must account for setup/hold margins relative to controlling logic.

Does CD74HCT640EE4 require external pull-up or pull-down resistors on unused inputs?

Yes. Per TI's layout guidelines, all unused inputs-including DIR, OE, and any unconnected An/Bn pins-must be terminated to VCC or GND with 1 kΩ to 1 MΩ resistors. Floating inputs risk undefined logic states, increased ICC, and potential oscillation. The CD74HCT640EE4 has no internal weak pull-ups or pull-downs.

Can CD74HCT640EE4 be used with a 3.3 V microcontroller interface?

No-CD74HCT640EE4 requires 4.5–5.5 V supply and is not 3.3 V tolerant. Its inputs expect TTL thresholds (VIH ≥ 2.0 V), but driving it from a 3.3 V MCU may cause marginal VIH compliance. For 3.3 V systems, use CD74HC640E (2–6 V) or add discrete level-shifting; never apply 3.3 V to VCC of CD74HCT640EE4.

What is the thermal resistance (RθJA) of CD74HCT640EE4 in its PDIP package?

The CD74HCT640EE4 in PDIP-20 (N package) has a junction-to-ambient thermal resistance (RθJA) of 69°C/W, as specified in the datasheet's Thermal Information table. This value assumes standard JEDEC 2S2P test board conditions; actual board layout, copper area, and airflow will affect real-world thermal performance.

How does the DIR pin behavior differ from conventional direction-control signals in other transceivers?

The DIR pin on CD74HCT640EE4 is edge-insensitive and level-triggered: it statically defines direction (A→B when DIR = L, B→A when DIR = H) without requiring synchronization to clocks or handshaking. Unlike some transceivers, DIR has no setup/hold timing constraints relative to OE or data edges-simplifying control logic design and eliminating metastability concerns.