Texas Instruments SN74HC540PWT

Overview

SN74HC540PWT 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 delivers ±6 mA output drive at 5 V, features typical propagation delay of 8 ns, and supports up to 15 LSTTL loads - enabling direct connection to legacy TTL buses in industrial control and instrumentation applications.

For engineers reviewing the SN74HC540PWT datasheet, SN74HC540PWT pinout, SN74HC540PWT application, or SN74HC540PWT equivalent, key selection criteria include its inverted logic function, dual 3-state enable (OE1/OE2) architecture, TSSOP-20 package footprint, and compatibility with HC-series timing and voltage thresholds across 2–6 V operation.

Technical Context

The SN74HC540PWT implements eight independent inverting buffers, each with high-impedance (3-state) output control via a 2-input NOR gate formed by OE1 and OE2 inputs - either high disables all outputs. Its input-to-output signal path is fully buffered and non-latching, supporting bidirectional bus isolation when paired with complementary devices.

It operates within −40°C to +85°C ambient temperature, uses standard CMOS silicon process, and exhibits rail-to-rail output swing with input thresholds referenced to VCC (VIH = 70% VCC, VIL = 30% VCC). The device requires no external biasing and draws ≤80 μA ICC at 6 V, making it suitable for low-power logic interfacing where signal inversion and bus contention prevention are required.

Key Specifications

Pinout & Package

TSSOP-20 package (6.50 mm × 4.40 mm, 1.2 mm max height), lead finish NIPDAU, moisture sensitivity level 1 (260°C peak reflow), RoHS compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC240PW and SN74LVC541APW, the SN74HC540PWT uniquely combines 2–6 V operation, inverted logic, and proven LSTTL load compatibility - making it the only choice for legacy 5 V bus inversion and isolation where voltage flexibility and polarity correction are jointly required.

Availability

SN74HC540PWT is available at Aetrix Electronics and suitable for industrial automation, test instrumentation, and embedded control applications requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for SN74HC540PWT 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 ICs, with decades of heritage in industry-standard logic families including 74HC.

The SN74HC540PWT belongs to TI's 74HC high-speed CMOS logic family, engineered for robust performance in industrial and commercial environments where wide supply range, low power, and bus-interface reliability are critical design requirements.

FAQ

What is the logic function of the SN74HC540PWT?

The SN74HC540PWT implements eight independent inverting buffers with 3-state outputs. Each output Yn equals NOT(An), and all outputs enter high-impedance state when either OE1 or OE2 is driven high. This behavior is confirmed in the functional table (Table 7-1) and block diagram of the official TI datasheet SCLS007F.

Does the SN74HC540PWT support 3.3 V operation?

Yes, the SN74HC540PWT supports 3.3 V operation within its specified 2 V to 6 V supply range. At 3.3 V, it meets recommended operating conditions with VIH ≥ 2.31 V and VIL ≤ 0.99 V, and delivers typical tpd = 10 ns (CL = 50 pF), making it fully compatible with 3.3 V CMOS systems while retaining 5 V tolerance.

What is the thermal resistance (RθJA) of the SN74HC540PWT?

The SN74HC540PWT in TSSOP-20 package has a junction-to-ambient thermal resistance (RθJA) of 131.8°C/W, as specified in Section 5.3 of the TI datasheet SCLS007F (Rev F, July 2022). This value assumes standard JEDEC 2-layer board conditions and informs derating calculations for continuous operation at elevated ambient temperatures.

Can unused inputs on the SN74HC540PWT be left floating?

No. All unused inputs on the SN74HC540PWT must be tied to VCC or GND to prevent undefined logic states and excessive ICC. Section 5.2 of the TI datasheet explicitly states that unused inputs must be held at valid logic levels, and TI application report SCBA004 details risks of floating CMOS inputs including increased power consumption and oscillation.

Is the SN74HC540PWT pin-compatible with the SN74HC240?

Yes, the SN74HC540PWT is pin-compatible with the SN74HC240 series in the same package variant (e.g., TSSOP-20), sharing identical pin configuration and electrical characteristics except for logic polarity: SN74HC540PWT provides inverted outputs (Y = NOT(A)), while SN74HC240 provides non-inverted outputs (Y = A).