Texas Instruments SN74HC540N

Overview

SN74HC540N from Texas Instruments is an octal inverting buffer/line driver with 3-state outputs, designed for bus-oriented applications requiring high-current drive and logic-level translation across 2 V to 6 V. It delivers ±6 mA output drive at 5 V, features typical propagation delay of 8 ns, and supports up to 15 LSTTL loads-enabling direct interface with legacy TTL buses in industrial control backplanes.

For engineers reviewing the SN74HC540N datasheet, SN74HC540N pinout, SN74HC540N application, or SN74HC540N equivalent, key selection considerations include its inverted data path, dual 3-state enable (OE1/OE2) NOR logic, PDIP-20 package compatibility with through-hole prototyping, and verified operation from −40°C to +85°C in noise-sensitive digital I/O expansion designs.

Technical Context

The SN74HC540N implements eight independent inverting buffers, each with complementary input-to-output polarity and shared 3-state control via two active-low enable inputs (OE1, OE2) wired as a NOR gate-ensuring all outputs enter high-impedance state if either enable is asserted high. Its CMOS design achieves low static current (≤80 μA ICC max) while maintaining rail-to-rail output swing and robust noise immunity.

Input thresholds are specified at VIH = 3.15 V and VIL = 1.35 V under 4.5 V supply, supporting reliable interfacing with both 3.3 V and 5 V logic families. The device uses a data flow-through pinout-inputs on one side (pins 1–8, 19–20), outputs on the opposite side (pins 11–18)-reducing PCB trace crossovers in dense bus routing.

Key Specifications

Pinout & Package

SN74HC540N is housed in a 20-pin Plastic Dual In-line Package (PDIP) with 0.3-inch body width and 0.1-inch lead pitch, optimized for breadboard and prototype board use. The package features a data flow-through layout: inputs occupy pins 1–8 and 19–20; outputs occupy pins 11–18; power/ground and enables occupy center positions.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT540N and 74LCX540M, the SN74HC540N provides the broadest supply voltage flexibility (2–6 V), maintains full 5 V tolerance, and retains industry-standard PDIP-20 mechanical compatibility-making it the preferred choice for mixed-voltage prototyping, industrial retrofits, and educational platforms where layout stability and voltage adaptability are critical.

Availability

SN74HC540N is available at Aetrix Electronics and suitable for industrial PLC I/O expansion, legacy bus interface adapters, test equipment signal conditioning, and embedded system debug port multiplexing requiring stable component supply across extended product lifecycles.

Supply support for SN74HC540N 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 logic solutions, with decades of heritage in industry-standard logic families.

The SN74HC540N belongs to TI's 74HC high-speed CMOS logic product line, engineered for robust performance in industrial control, instrumentation, and bus-interface applications where reliability, wide voltage operation, and proven pin compatibility are essential.

FAQ

What is the maximum output current rating for SN74HC540N?

The SN74HC540N is rated for continuous output current of ±35 mA per output pin under absolute maximum conditions, but its recommended operating output drive is ±6 mA at 5 V supply. This ±6 mA specification ensures stable 3-state transitions, meets LSTTL load requirements, and maintains timing integrity within datasheet limits-making it suitable for driving moderate-capacitance buses without external buffering.

Does SN74HC540N support 3.3 V logic levels?

Yes, SN74HC540N fully supports 3.3 V operation: its recommended supply range includes 3.3 V, input thresholds scale proportionally (VIH ≈ 2.31 V, VIL ≈ 0.99 V at 3.3 V), and it delivers rail-to-rail outputs. At 3.3 V, it provides ±4 mA drive and typical tpd of 10 ns (CL = 50 pF), making SN74HC540N ideal for mixed-voltage systems bridging 3.3 V microcontrollers to 5 V peripherals.

How does the 3-state enable logic work on SN74HC540N?

The SN74HC540N uses a 2-input NOR gate for 3-state control: both OE1 and OE2 are active-low inputs, and if either is driven high, all eight outputs immediately enter high-impedance state. This architecture allows flexible bus arbitration-for example, OE1 can be tied to a system reset signal while OE2 connects to a processor-controlled GPIO, giving layered control over bus access without additional logic gates.

Is SN74HC540N RoHS compliant?

Yes, SN74HC540N is RoHS compliant, as confirmed in TI's official packaging addendum: the PDIP-20 variant carries NIPDAU (nickel-palladium-gold) lead finish and is marked "Yes" under RoHS column. It meets EU Directive 2011/65/EU requirements and is suitable for commercial and industrial applications requiring environmentally compliant components.

Can SN74HC540N be used in place of SN74HC240?

No-SN74HC540N and SN74HC240 are functionally distinct: SN74HC540N provides inverted outputs (Y = NOT A), while SN74HC240 offers non-inverting outputs (Y = A). Though both are octal 3-state buffers in PDIP-20 packages with identical pinouts for power, ground, and enables, substituting them requires logic inversion elsewhere in the signal path or firmware-level compensation to maintain correct data polarity.