Texas Instruments SN74HCS240RKSR

Overview

SN74HCS240 from Texas Instruments is an octal inverting line driver IC with Schmitt-trigger inputs and 3-state outputs, designed for signal conditioning and bus interface in industrial control and automotive subsystems. It operates across 2V–6V supply, delivers ±7.8mA output drive at 6V, features 100nA typical ICC, and supports –40°C to +125°C ambient operation.

For engineers reviewing the SN74HCS240 datasheet, SN74HCS240 pinout, SN74HCS240 application, or SN74HCS240 equivalent, key selection criteria include its dual-bank 3-state enable architecture, hysteresis-based noise immunity (ΔVT ≥ 0.6V at 6V), propagation delay ≤16ns at 6V, and VQFN-20 (RKS) / VSSOP-20 (DGS) package compatibility.

Technical Context

The SN74HCS240 integrates eight independent CMOS inverters grouped into two banks of four, each controlled by a dedicated active-low OE pin (1OE and 2OE). Its Schmitt-trigger inputs provide hysteresis (VT+ − VT− = 0.6V min at 6V), enabling reliable operation with slow-rising or noisy signals without external filtering.

All outputs are balanced CMOS push-pull with 3-state capability; when OE is high, outputs enter high-impedance state with leakage ≤±2µA. The device uses standard CMOS logic levels but achieves TTL-compatible input thresholds via internal design-no external biasing required.

Key Specifications

Pinout & Package

SN74HCS240 is available in two RoHS-compliant packages: RKS (20-pin VQFN, 4.50mm × 2.50mm body) and DGS (20-pin VSSOP, 5.1mm × 4.9mm body). Both packages feature exposed thermal pads for enhanced thermal dissipation in high-density layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCS240PWR and MC74HC240ADTR2G, the SN74HCS240 offers superior thermal efficiency in compact layouts (83.2°C/W), tighter hysteresis control (0.6V min), and lower typical quiescent current-making it optimal for space-constrained, high-reliability industrial modules.

Availability

SN74HCS240 is available at Aetrix Electronics and suitable for industrial sensor interface, automotive body control, and programmable logic controller I/O expansion requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN74HCS240 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 connectivity technologies, with decades of experience in high-reliability logic and interface solutions.

The SN74HCS240 belongs to TI's HCS family of high-speed CMOS logic devices engineered for noise-immune signal conditioning in harsh electrical environments-targeting automotive, industrial automation, and test equipment markets.

FAQ

What is the maximum capacitive load the SN74HCS240 can drive while meeting all datasheet specifications?

The SN74HCS240 is characterized for CL = 50pF in switching specifications. While it can drive larger loads, timing parameters (tpd, ten, tdis) and output voltage margins (VOH/VOL) are guaranteed only up to 50pF. Exceeding this value increases propagation delay and may cause signal integrity issues unless compensated with series termination. For SN74HCS240, maintaining CL ≤ 50pF ensures compliance with the 6ns typical propagation delay and 0.33V VOL spec at 6V.

Can both OE pins of the SN74HCS240 be tied together and driven by a single controller signal?

Yes-1OE and 2OE can be connected to a common control line, allowing simultaneous enable/disable of all eight outputs. This configuration simplifies GPIO usage but eliminates independent bank control. When doing so, ensure the driving source can sink/source sufficient current for both inputs (combined II ≤ ±200nA), and verify that shared enable timing meets system-level sequencing requirements. The SN74HCS240 supports this mode per its functional table.

Does the SN74HCS240 require external pull-up resistors on its OE pins for proper power-up behavior?

Yes-TI recommends tying both 1OE and 2OE to VCC through pull-up resistors to ensure outputs remain in high-impedance state during power ramp-up. A 10kΩ resistor is typical, selected to overcome input leakage (±100nA) while limiting current to <0.5mA. Without pull-ups, undefined OE states could cause bus contention or excessive ICC transient current. This requirement applies specifically to SN74HCS240 due to its active-low enable architecture.

How does the Schmitt-trigger input of the SN74HCS240 improve performance with mechanical switch inputs?

The SN74HCS240's Schmitt-trigger inputs provide 0.6V minimum hysteresis at 6V, which suppresses multiple transitions caused by switch bounce lasting up to several milliseconds. Unlike standard CMOS inputs, it does not require external RC networks or firmware debouncing. This allows direct connection of SPST switches to SN74HCS240 inputs, with clean, single-edge outputs delivered to the host MCU-reducing BOM cost and software overhead in applications like panel controls or safety interlocks.

Is the thermal pad on the RKS package of the SN74HCS240 electrically connected internally?

No-the thermal pad on the SN74HCS240 RKS (VQFN-20) package is not internally connected to any die node. TI specifies it may be connected to GND for improved heat dissipation or left floating. It must never be connected to VCC or signal nets. Soldering the pad to a GND plane reduces θJA from 83.2°C/W to approximately 75°C/W in typical 2-layer boards, enhancing reliability in thermally demanding SN74HCS240 deployments.