onsemi 74VHCT240AN

Overview

74VHCT240AN from onsemi is an octal inverting 3-STATE buffer/line driver with two active-low output enables, designed for memory address and clock driving in 5 V bus systems. It delivers 3.6 ns typical propagation delay at 5 V, supports 5.5 V absolute max input/output voltage, and operates across −40°C to +85°C for industrial embedded control applications.

For engineers reviewing the 74VHCT240AN datasheet, pinout, applications, or equivalent options, key selection criteria include guaranteed 3-STATE output disable timing (≤13.5 ns), ±25 mA output drive per pin, 5 V CMOS/TTL compatibility, and Pb-free TSSOP-20 packaging suitable for high-density PCB layouts.

Technical Context

The 74VHCT240AN implements dual independent 4-bit inverting buffers, each controlled by its own active-low enable (OE1, OE2). All eight outputs enter high-impedance state when either enable is HIGH, enabling bidirectional bus arbitration without external logic.

It features silicon-gate CMOS technology with input/output protection circuits allowing safe 0–5.5 V signal application regardless of VCC, supporting mixed-voltage interfacing between 5 V and 3 V domains and battery-backup system integration.

Key Specifications

Pinout & Package

74VHCT240AN is housed in a Pb-free TSSOP-20 package (Case 948AQ, 4.4 mm × 6.5 mm), optimized for automated SMT assembly and thermal performance in space-constrained designs.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal inverting 3-STATE buffer applications.

Compared with 74HCT240N and SN74LVC240APWR, the 74VHCT240AN uniquely combines 5 V operation, 5.5 V tolerant I/O, ultra-low ICC, Pb-free packaging, and pin/function compatibility with legacy HCT - making it the optimal drop-in upgrade for industrial 5 V systems requiring reliability and compliance.

Availability

74VHCT240AN is available at Aetrix Electronics and suitable for industrial control panels, microcontroller-based instrumentation, and legacy 5 V bus expansion modules requiring stable component supply and long-term lifecycle support.

Supply support for 74VHCT240AN 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power, analog, sensor, and logic solutions for automotive, industrial, and cloud infrastructure markets.

The 74VHCT240AN belongs to the VHCT logic family, engineered specifically for high-speed, low-power 5 V TTL-compatible interfacing in industrial and embedded systems where robustness and mixed-voltage operation are essential.

FAQ

What is the maximum operating frequency supported by the 74VHCT240AN?

The 74VHCT240AN does not specify a maximum clock frequency in its datasheet because it is a combinatorial buffer-not a clocked device. Its usable frequency limit depends on propagation delay and system timing margins: with 5.6 ns typical tPLH/tPHL at CL = 15 pF, it reliably supports data/address bus toggling up to ~100 MHz in well-terminated, low-capacitance layouts. For precise timing analysis, designers must calculate setup/hold windows using actual trace capacitance and load conditions for their 74VHCT240AN implementation.

Can the 74VHCT240AN be used to interface 3.3 V logic to a 5 V bus?

No-the 74VHCT240AN is a 5 V-only supply device (VCC = 4.5–5.5 V) and is not rated for 3.3 V operation. While its inputs tolerate 0–5.5 V regardless of VCC, applying 3.3 V to VCC violates the recommended operating condition and risks undefined output levels and increased ICC. To interface 3.3 V logic to a 5 V bus, use a dedicated level translator such as the TXB0108 or select a 3.3 V–tolerant buffer like the SN74LVC240A instead of the 74VHCT240AN.

Does the 74VHCT240AN require external pull-up or pull-down resistors on unused inputs?

Yes-per the datasheet's Recommended Operating Conditions (Note 5), all unused inputs of the 74VHCT240AN must be tied to a valid logic level (GND or VCC) to prevent floating nodes that cause excessive ICC, noise susceptibility, or oscillation. Leaving inputs unconnected may increase supply current beyond the 4 µA max specification and compromise noise immunity. Outputs may be left open in 3-STATE mode, but inputs must never float-this applies to all eight I0–I7 pins and both OE1/OE2 enables in the 74VHCT240AN.

Is the 74VHCT240AN pin-compatible with the 74VHC240?

No-the 74VHCT240AN and 74VHC240 are not pin-compatible. Although both are octal inverting 3-STATE buffers in TSSOP-20 packages, the 74VHC240 uses different enable logic (active-HIGH OE) and has distinct pin assignments for OE and outputs. The 74VHCT240AN is explicitly pin- and function-compatible only with the 74HCT240 per its datasheet, not the VHC family. Substituting 74VHC240 for 74VHCT240AN would invert enable polarity and disrupt bus control timing, making it incompatible without PCB redesign.

What is the thermal resistance (θJA) of the 74VHCT240AN in its TSSOP-20 package?

The 74VHCT240AN in TSSOP-20 (Case 948AQ) has a junction-to-ambient thermal resistance (θJA) of 150°C/W, measured on a 76 mm × 114 mm FR4 board with 2-ounce copper and no airflow (per JESD51-7). This value assumes minimum pad spacing; actual θJA improves with enhanced copper pour or thermal vias. At maximum 833 mW power dissipation, this yields a worst-case junction temperature rise of 125°C above ambient-so operation at +85°C ambient requires derating or heatsinking to stay below the +150°C TJ limit. This thermal spec is confirmed in the Absolute Maximum Ratings table of the 74VHCT240AN datasheet.