Toshiba Semiconductor and Storage 74LCX240FT

Overview

74LCX240FT from Toshiba is an inverting 3-state octal bus buffer IC designed for low-voltage memory address and data bus driving in 3.3 V systems, with 5 V tolerant inputs/outputs, 6.5 ns max propagation delay (VCC = 3.0–3.6 V), ±24 mA output drive, and TSSOP20B package. It supports bidirectional voltage-level translation between 3.3 V logic domains and legacy 5 V peripherals.

For engineers reviewing the 74LCX240FT datasheet, 74LCX240FT pinout, 74LCX240FT application, or 74LCX240FT equivalent, key selection criteria include 3.3 V operation with 5 V I/O tolerance, dual active-low output enables for bus isolation, high-speed 3-state control timing, and compatibility with 74LVC/ALVC240 logic families in space-constrained PCB layouts.

Technical Context

The 74LCX240FT implements eight independent inverting buffer channels, each with separate 3-state control via two shared active-low OE pins (OE1̅ and OE2̅), enabling grouped enable/disable of four buffers per control signal. Its CMOS silicon monolithic structure ensures rail-to-rail input thresholds and robust static discharge protection on all pins.

Designed for mixed-voltage system interfacing, it operates across VCC = 1.65–3.6 V while accepting input voltages up to 5.5 V and driving outputs to 5.5 V - eliminating external level shifters when connecting 3.3 V controllers to 5 V memory or peripheral buses. Power-down leakage remains ≤±5 µA at VCC = 0 V.

Key Specifications

Pinout & Package

TSSOP20B: 20-pin thin shrink small outline package, 0.65 mm pitch, 6.5 mm × 4.4 mm body, 0.071 g typical weight, JEDEC MO-153 compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74LCX240FT, the 74LVC240APW offers cost savings in 3.3 V-only systems but lacks 5 V I/O safety margin, while SN74LVCH240AQPWRQ1 adds automotive qualification and extended VCC range at no PCB layout penalty - making it ideal for safety-critical vehicle electronics.

Availability

74LCX240FT is available at Aetrix Electronics and suitable for industrial control systems, test instrumentation, and legacy peripheral interface designs requiring stable component supply, long-term lifecycle support, and guaranteed RoHS-compliant sourcing.

Supply support for 74LCX240FT 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

Toshiba Electronic Devices & Storage Corporation designs and manufactures high-reliability semiconductor components for industrial, automotive, and consumer applications, with leadership in logic ICs, power devices, and memory solutions.

The 74LCX series targets low-voltage, high-speed digital interfacing in mixed-signal embedded systems - specifically engineered to bridge voltage gaps between legacy 5 V infrastructure and modern 3.3 V processors without sacrificing speed or noise immunity.

FAQ

What is the maximum operating frequency supported by the 74LCX240FT?

The 74LCX240FT does not specify a maximum clock frequency directly, but its 6.5 ns maximum propagation delay (tpd) at VCC = 3.0–3.6 V implies reliable operation up to approximately 100 MHz for bus toggle applications. Actual usable frequency depends on load capacitance, trace length, and signal integrity margins - design validation at target data rates is recommended using the AC test conditions in the Toshiba datasheet Rev. 3.0.A.

Can the 74LCX240FT safely interface a 3.3 V microcontroller with a 5 V EEPROM?

Yes, the 74LCX240FT can safely interface a 3.3 V microcontroller with a 5 V EEPROM because its inputs and outputs are rated for 0 V to 5.5 V, and it operates with VCC = 1.65–3.6 V. This allows the device to translate logic levels bidirectionally without external components - the microcontroller drives 3.3 V signals into the 74LCX240FT inputs, and the 74LCX240FT outputs drive valid 5 V-compatible logic levels to the EEPROM, all while powered solely from the 3.3 V rail.

Does the 74LCX240FT require pull-up or pull-down resistors on unused inputs?

Yes, unused inputs on the 74LCX240FT must be tied to either VCC or GND to prevent floating states that could cause excessive current draw or unpredictable output behavior. The Toshiba datasheet explicitly states this requirement in Section 10 (Operating Ranges, Note). Leaving inputs unconnected violates the specified operating conditions and may lead to increased ICC or functional instability - especially under temperature variation or EMI exposure.

Is the 74LCX240FT pin-compatible with standard 74HC240 devices?

No, the 74LCX240FT is not pin-compatible with standard 74HC240 devices. While both are octal inverting 3-state buffers, the 74HC240 uses a 20-pin DIP or SOIC package with different pin assignments (e.g., OE pins located at pins 1 and 19 in HC, but pins 1 and 19 in LCX serve OE1̅ and OE2̅ respectively - matching LVC, not HC). The 74LCX240FT is explicitly pin- and function-compatible with 74LVC240, not 74HC240.

What is the thermal performance of the 74LCX240FT in continuous operation?

The 74LCX240FT has a maximum junction temperature of +150 °C and operates over –40 °C to +85 °C ambient. Its typical power dissipation capacitance is 25 pF, enabling accurate dynamic power calculation (ICC(opr) = CPD × VCC × fIN + ICC/8). At 3.3 V and 10 MHz with 50 pF load, total ICC remains below 5 mA - resulting in negligible self-heating in TSSOP20B package even in enclosed industrial enclosures without forced airflow.