STMicroelectronics 74LCX240TTR

Overview

74LCX240TTR from STMicroelectronics is a low-voltage CMOS octal bus buffer with 3-state inverting outputs, 5V-tolerant I/O, and symmetrical ±24 mA drive at VCC = 3.0–3.6 V. It operates from 2.0 V to 3.6 V, delivers 6.5 ns max propagation delay at 3 V, and supports PCI bus levels - used in 3.3 V memory address driver interfaces with 5 V legacy system interconnect.

For engineers reviewing the 74LCX240TTR datasheet, 74LCX240TTR pinout, 74LCX240TTR application, or 74LCX240TTR equivalent, key selection criteria include 5V-tolerant I/O compatibility, balanced tPLH/tPHL timing, output disable/enable timing (tPZH/tPHZ ≤ 9.2 ns), and latch-up immunity exceeding 500 mA per JESD17.

Technical Context

The 74LCX240 implements dual 4-bit inverting 3-state buffers with independent active-low output enables (1G and 2G). All inputs and outputs tolerate 0–5.5 V regardless of VCC (2.0–3.6 V), enabling safe interfacing between 3.3 V logic domains and 5 V buses without level shifters.

Its C2MOS sub-micron process ensures low ICC (≤10 µA quiescent) and high noise immunity, with input leakage ≤±5 µA and high-impedance output leakage ≤±5 µA. Propagation skew is guaranteed ≤1.0 ns, supporting synchronous multi-bit data routing in memory and address paths.

Key Specifications

Pinout & Package

TSSOP-20 package (JEDEC MO-153, 6.5 mm × 4.4 mm, 0.65 mm pitch); 1.2 mm height, lead-free and RoHS compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC240APWR and 74ALVC240PW, the 74LCX240TTR uniquely combines 5 V-tolerant I/O, symmetrical ±24 mA drive across its full 2.0–3.6 V range, and JESD17-compliant latch-up immunity - making it the only option for robust, translator-free 3.3 V/5 V bus bridging in industrial and telecom infrastructure.

Availability

74LCX240TTR is available at Aetrix Electronics and suitable for memory address buffering, PCI bus interfacing, hot-swappable backplane slots, and low-power embedded controller buses requiring stable component supply and long-term industrial availability.

Supply support for 74LCX240TTR 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, specializing in automotive, industrial, power, and microcontroller solutions with vertical manufacturing and broad IP portfolio.

The 74LCX logic family was designed specifically for mixed-voltage system interfacing - delivering AC/ACT-speed performance at 3.3 V with 5 V-tolerant I/O, targeting telecom infrastructure, industrial PLCs, and legacy-compatible embedded computing.

FAQ

Can 74LCX240TTR be operated at 1.8 V?

No. The recommended operating VCC range is 2.0 V to 3.6 V per Table 5. At 1.8 V, DC parameters including VIH/VIL thresholds and output drive fall outside specification, and propagation delay increases unpredictably. Data retention is guaranteed down to 1.5 V, but functional operation requires ≥2.0 V.

Is output enable timing (tPZH/tPHZ) dependent on load capacitance?

Yes. The specified tPZH ≤ 9.2 ns and tPHZ ≤ 8.3 ns (Table 8) are measured with CL = 50 pF and RL = 500 Ω per Figure 3. With lower load capacitance (e.g., 15 pF), enable/disable times improve by ~30%; with higher loads (>75 pF), timing degrades nonlinearly and may violate setup/hold windows in high-speed bus protocols.

Does 74LCX240TTR require external pull-up or pull-down resistors on unused inputs?

No. Input leakage is ≤±5 µA (Table 6), and inputs are fully rail-tolerant (0–5.5 V). However, floating inputs must be avoided: unconnected inputs can drift into the undefined switching region (0.8–2.0 V at VCC = 3.0 V), causing increased ICC and potential oscillation. Tie unused inputs to VCC or GND via PCB traces - no resistors needed.

How does the 5 V tolerance work without internal clamping diodes to VCC?

The 74LCX240TTR uses oxide-isolated input structures with extended gate oxide breakdown voltage and optimized well implants - not conventional silicon diodes. This allows safe 0–5.5 V input/output voltage swing even when VCC = 2.0 V, eliminating forward conduction paths that cause back-powering or latch-up in standard CMOS. Absolute maximum ratings confirm no current path exists above VCC + 0.5 V.