Texas Instruments SN74HCT540N

Overview

SN74HCT540N from Texas Instruments is an octal inverting buffer/line driver with 3-state outputs, designed for bus interface and load driving in 5-V TTL-compatible digital systems. It operates from 4.5 V to 5.5 V, delivers ±6-mA output drive per channel, exhibits typical propagation delay of 12 ns at 5.5 V, and draws ≤80 µA ICC in quiescent state - enabling reliable signal buffering in industrial control backplanes and legacy data buses.

For engineers reviewing the SN74HCT540N datasheet, SN74HCT540N pinout, SN74HCT540N application, or SN74HCT540N equivalent, key selection criteria include its inverted data path, dual 3-state enable (OE1/OE2) NOR logic, data flow-through pinout for PCB layout simplification, and compatibility with LSTTL loads (up to 15 per output).

Technical Context

The SN74HCT540N implements eight independent inverting buffer channels, each with high-current 3-state outputs controlled by a dual-input NOR gate (OE1 and OE2). When either enable input is high, all outputs enter high-impedance mode - critical for bus contention avoidance in shared-data-path architectures.

Its HCT logic family ensures TTL-voltage-level compatibility on inputs while maintaining CMOS power efficiency. The data flow-through pinout places all eight A inputs on one side (pins 1–8) and all eight Y outputs on the opposite side (pins 13–20), minimizing trace crossovers and reducing parasitic coupling in dense PCB layouts.

Key Specifications

Pinout & Package

SN74HCT540N uses a 20-pin plastic dual in-line package (PDIP-N), 6.35 mm wide, with 2.54 mm pitch and 0.51 mm lead thickness. Pin 1 is marked by a notch or bevel; leads are tin-lead (NIPDAU) finish, 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 SN74HCT240N and 74ACT540PC, the SN74HCT540N uniquely balances TTL compatibility, low static power, and inverted data flow - making it the preferred choice for retrofitting legacy 5-V bus systems where signal inversion is already accounted for in firmware or logic design.

Availability

SN74HCT540N is available at Aetrix Electronics and suitable for industrial automation backplanes, legacy computer bus interfaces, and embedded diagnostic subsystems requiring stable component supply over extended production lifecycles.

Supply support for SN74HCT540N 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 founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74HCT540N belongs to TI's 74HCT logic family - engineered for seamless integration between TTL and CMOS systems, emphasizing voltage compatibility, low power, and robust bus-driving capability in 5-V digital infrastructure.

FAQ

What is the function of the dual OE inputs on the SN74HCT540N?

The SN74HCT540N uses a 2-input NOR gate for 3-state control: if either OE1 or OE2 is high, all eight outputs go high-impedance. This architecture allows flexible bus arbitration - for example, OE1 can be driven by a master controller while OE2 responds to a fault signal, ensuring fail-safe bus release. The SN74HCT540N does not require both enables to be asserted simultaneously.

Does the SN74HCT540N support mixed-voltage operation (e.g., 3.3-V inputs with 5-V supply)?

No. The SN74HCT540N inputs are TTL-voltage compatible (VIH = 2 V min, VIL = 0.8 V max) but not guaranteed for 3.3-V logic levels. While 3.3-V CMOS outputs may often meet VIH, TI specifies no guaranteed switching at VCC = 5 V with VI < 2 V. For robust 3.3-V-to-5-V interfacing, use a dedicated level translator or the 74ACT540 instead. The SN74HCT540N is optimized for 5-V-only systems.

How should unused inputs be handled on the SN74HCT540N?

All unused inputs on the SN74HCT540N - including A1–A8, OE1, and OE2 - must be tied to VCC or GND to prevent floating nodes, which cause increased ICC, noise susceptibility, and potential latch-up. TI Application Report SCBA004 explicitly mandates this. Leaving any input unconnected violates recommended operating conditions and risks erratic behavior. The SN74HCT540N has no internal pull-ups or pull-downs.

Is the SN74HCT540N pin-compatible with the SN74HCT240N?

Yes - the SN74HCT540N and SN74HCT240N share identical 20-pin PDIP (N), SOIC (DW), and CDIP (J) packages and pinouts. The only functional difference is inversion: SN74HCT540N outputs inverted data (Y = NOT A), while SN74HCT240N outputs non-inverted data (Y = A). This makes them drop-in replacements where signal polarity is managed elsewhere in the design.

What is the maximum capacitive load the SN74HCT540N can drive while maintaining specified timing?

The SN74HCT540N switching characteristics are characterized at CL = 50 pF and CL = 150 pF. At 5.5 V, tpd increases from 12 ns (50 pF) to 19 ns (150 pF); output rise/fall times scale similarly. Driving >150 pF risks violating setup/hold windows in synchronous buses. For heavier loads, add series termination or use multiple SN74HCT540N devices in parallel - the SN74HCT540N itself does not specify performance beyond 150 pF.