Texas Instruments SN74HCT245PWT

Overview

SN74HCT245PWT from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for asynchronous bidirectional data transfer between A and B buses in 5-V logic systems. It features ±6-mA output drive at 5 V, 14-ns typical propagation delay (VCC = 5.5 V), and operates across –40°C to +85°C. It serves as a high-current buffer in ribbon-cable and backplane interfaces where MCU/FPGA drive strength is insufficient.

For engineers reviewing the SN74HCT245PWT datasheet, SN74HCT245PWT pinout, SN74HCT245PWT application, or SN74HCT245PWT equivalent, key selection criteria include direction-control logic level compatibility, 3-state isolation timing (ten/tdis ≤ 52 ns), 5-V supply tolerance (4.5–5.5 V), and thermal performance in TSSOP-20 packaging.

Technical Context

The SN74HCT245PWT implements a dual-rail CMOS HCT logic family interface with active-low output enable (OE) and unidirectional direction control (DIR). Its TTL-compatible inputs accept 0.8 V/2.0 V thresholds, while outputs deliver balanced ±6-mA drive into LSTTL loads without external pull-ups.

Propagation delay is tightly controlled (14–25 ns over voltage/temperature), and switching characteristics are specified at CL = 50 pF and CL = 150 pF. The device supports bus isolation via high-impedance outputs when OE is high, and avoids contention through strict functional mode control per Table 8-1.

Key Specifications

Pinout & Package

TSSOP-20 package (PW), 6.50 mm × 4.40 mm body size, 0.65-mm lead pitch, RoHS-compliant NIPDAU finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal bus transceiver applications.

Compared with SN74HCT245PWT, SN74HCT245DBR offers superior thermal performance in space-constrained industrial PCBs, while SN74LVC245APWR enables 3.3-V domain integration but mandates full voltage-domain redesign and forfeits 5-V TTL compatibility.

Availability

SN74HCT245PWT is available at Aetrix Electronics and suitable for factory automation interfaces, telecom line card backplanes, and industrial motor drive control buses requiring stable component supply across extended product lifecycles.

Supply support for SN74HCT245PWT 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 over 50 years of innovation in industrial and automotive electronics.

The SN74HCT245PWT belongs to TI's 74HCT logic family, engineered for robust 5-V TTL-compatible bus interfacing in noise-prone industrial environments-prioritizing drive strength, timing predictability, and temperature resilience.

FAQ

What is the maximum operating temperature for the SN74HCT245PWT?

The SN74HCT245PWT is rated for operation from –40°C to +85°C ambient temperature. This industrial-grade range ensures reliable functionality in factory automation cabinets, telecom equipment enclosures, and motor drive control panels without derating. Thermal metrics (RθJA = 94.9°C/W) confirm safe operation under full 6-mA load at 85°C ambient when properly mounted on FR-4 with standard copper pour.

Does the SN74HCT245PWT support 3.3-V logic inputs?

No, the SN74HCT245PWT does not reliably support 3.3-V logic inputs. Its input thresholds are fixed at VIH = 2.0 V and VIL = 0.8 V under 4.5–5.5 V supply-designed for 5-V TTL compatibility. A 3.3-V high signal (typically 3.3 V) meets VIH, but marginal cases below 2.0 V may cause undefined states. For mixed-voltage systems, use level translators or select 74LVC-family devices instead of the SN74HCT245PWT.

How does the direction control (DIR) pin function in the SN74HCT245PWT?

The DIR pin on the SN74HCT245PWT determines data flow direction: logic high enables transmission from Port A to Port B; logic low enables transmission from Port B to Port A. DIR is sampled asynchronously and has no internal synchronization-its state must be stable before enabling OE. This allows dynamic reversal of bus traffic without reset, making the SN74HCT245PWT ideal for half-duplex protocols like printer command/response sequences.

What is the recommended bypass capacitor for the SN74HCT245PWT VCC pin?

Texas Instruments recommends a 0.1-µF ceramic capacitor placed as close as possible to the VCC pin (Pin 20) of the SN74HCT245PWT. This minimizes high-frequency supply noise generated during output switching. For systems with multiple SN74HCT245PWT devices or high-speed clock domains, paralleling a 1-µF capacitor improves low-frequency decoupling. Layout guidelines specify placement within 3 mm of the pin with short, wide traces to reduce inductance.

Can unused channels of the SN74HCT245PWT be left floating?

No, unused channels of the SN74HCT245PWT must not be left floating. All unused A and B pins (e.g., A7, A8, B7, B8) must be tied to either VCC or GND using ≥10-kΩ resistors to prevent undefined logic states, increased ICC, and potential oscillation. TI's layout guidelines explicitly prohibit floating I/Os-even when OE is high-because input sections remain active and susceptible to noise coupling. This requirement applies universally across all channel counts used in the SN74HCT245PWT design.