Texas Instruments SN74HC540NS

Overview

SN74HC540NS from Texas Instruments is an octal inverting buffer/line driver with 3-state outputs, designed for bus interface and data routing in 2–6 V digital systems. It features ±6-mA output drive at 5 V, typical propagation delay of 8 ns, low ICC (80 μA max), and data flow-through pinout enabling simplified PCB layout.

For engineers reviewing the SN74HC540NS datasheet, SN74HC540NS pinout, SN74HC540NS application, or SN74HC540NS equivalent, this page delivers verified electrical specs, thermal metrics, functional modes, package dimensions, and real-world use cases - all confirmed for the SO (NS) 20-pin variant.

Technical Context

The SN74HC540NS implements eight independent inverting buffers, each with high-current 3-state outputs controlled by a dual-input NOR gate (OE1/OE2). A high on either OE input places all outputs in high-impedance state, enabling bidirectional bus control without external logic.

Its CMOS design ensures compatibility with LSTTL loads (up to 15 units), operates across 2–6 V supply range, and maintains low input current (≤1 μA) and low power consumption - critical for mixed-voltage industrial and embedded interfaces.

Key Specifications

Pinout & Package

SOP (SO) 20-pin package, 15.00 mm × 5.30 mm body size, 1.27 mm lead pitch, gull-wing leads, RoHS-compliant NiPdAu finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC540NS, SN74HC240N preserves pinout and voltage range but reverses logic polarity, while SN74LVC541APW offers superior speed and density at the cost of 5 V incompatibility and reduced drive strength - both require functional validation before substitution.

Availability

SN74HC540NS is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy microcontroller expansion, test equipment signal routing, and automotive body control modules requiring stable component supply and long-term manufacturability.

Supply support for SN74HC540NS 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 SN74HC540NS belongs to TI's 74HC high-speed CMOS logic product line, engineered for interoperability with legacy TTL systems while delivering low power, wide voltage operation, and robust noise immunity in industrial control and instrumentation.

FAQ

What is the maximum operating temperature for SN74HC540NS?

The SN74HC540NS has a specified operating free-air temperature range of −40°C to +85°C. Its junction-to-ambient thermal resistance is 113.4 °C/W, so sustained operation near 85°C ambient requires adequate PCB copper area and airflow. The device remains functional up to 150°C junction temperature, but reliability degrades above rated ambient limits. Always verify thermal performance in final layout using TI's thermal simulation guidelines.

Does SN74HC540NS support 3.3 V logic levels?

Yes, SN74HC540NS fully supports 3.3 V operation: its recommended supply range is 2 V to 6 V, and input thresholds scale with VCC (VIH = 2.0 V min at 3.3 V, VIL = 0.99 V max). Output VOH/VOL meet 3.3 V LVTTL requirements (≥2.4 V high, ≤0.4 V low at 6 mA load), making it compatible with 3.3 V microcontrollers, FPGAs, and peripherals without level translation.

How do the two output-enable inputs (OE1 and OE2) work on SN74HC540NS?

The SN74HC540NS uses a 2-input NOR gate for 3-state control: if either OE1 or OE2 is driven high, all eight outputs enter high-impedance (Z) state. Both must be low to enable normal inverted buffering. This architecture allows flexible bus arbitration - for example, OE1 can serve as global enable while OE2 acts as local channel select, or both tied together for simple single-control operation.

Can SN74HC540NS replace SN74HC240 in an existing design?

SN74HC540NS and SN74HC240 share identical pinout, timing, drive strength, and package options, but differ in logic polarity: SN74HC540NS inverts inputs (A → ¬Y), while SN74HC240 passes them true (A → Y). Direct replacement is possible only if the downstream logic accommodates inversion - otherwise, redesign or external inverters are needed. Verify signal polarity in timing diagrams before substitution.

Is SN74HC540NS RoHS compliant and lead-free?

Yes, SN74HC540NS is RoHS compliant and features NiPdAu lead finish with no lead content. Per TI's packaging documentation, the NS package variant carries "Yes" in the RoHS column and "NIPDAU" in lead finish. It meets JEDEC J-STD-020 moisture sensitivity Level-1 (unlimited floor life at ≤30°C/60% RH) and is qualified for reflow at 260°C peak per JEDEC standards.