Texas Instruments SN74HCS245DGSR

Overview

SN74HCS245 from Texas Instruments is an octal bus transceiver IC with 3-state outputs and Schmitt-trigger inputs, operating across 2 V to 6 V. It provides bidirectional data flow control via DIR pin, output enable/disable via active-low OE, and ±7.8-mA drive at 6 V. Used in industrial I/O expansion where noise immunity and level translation between mixed-voltage subsystems are required.

For engineers reviewing the SN74HCS245 datasheet, SN74HCS245 pinout, SN74HCS245 application, or SN74HCS245 equivalent, key selection criteria include Schmitt-trigger hysteresis (ΔVT ≥ 0.6 V at 6 V), propagation delay ≤13 ns at 6 V, 3-state output leakage <2 µA, wide temperature range (–40°C to +125°C), and dual-package availability (VQFN-20 and SOT-20).

Technical Context

The SN74HCS245 implements eight independent bidirectional transceivers, each with complementary A↔B paths controlled by a shared DIR signal and globally enabled/disabled by OE. Its CMOS architecture supports rail-to-rail input/output swing and balanced sourcing/sinking capability.

Schmitt-trigger inputs provide defined hysteresis (VT+ − VT− = 0.6 V min at 6 V), enabling reliable operation with slow-edge or noisy signals without external conditioning. The 3-state outputs support bus sharing and hot-swap compatibility, with off-state leakage limited to 2 µA max at 6 V.

Key Specifications

Pinout & Package

SN74HCS245 is available in two surface-mount packages: RKS (20-pin VQFN, 4.5 mm × 2.5 mm) and DGS (20-pin SOT, 5.1 mm × 3.0 mm). Both packages feature identical pin numbering and function mapping per TI SCLS879A.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVCH245A and 74LVC245, the SN74HCS245 uniquely combines wide 2–6-V operation, integrated Schmitt-trigger inputs for noise rejection, and industrial temperature range - making it the only option among the three qualified for mixed-voltage, high-noise, and extended-temperature applications.

Availability

SN74HCS245 is available at Aetrix Electronics and suitable for industrial sensor interfaces, microcontroller I/O expansion, automotive body control modules, and noisy industrial bus isolation requiring stable component supply across extended temperature and voltage ranges.

Supply support for SN74HCS245 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 company specializing in analog and embedded processing solutions, with leadership in logic, power management, and signal chain technologies.

The SN74HCS245 belongs to TI's HCS family of high-speed CMOS logic devices designed for robust, low-power, mixed-voltage digital interfacing in industrial, automotive, and communications systems.

FAQ

What is the maximum capacitive load the SN74HCS245 can drive while meeting all datasheet specifications?

The SN74HCS245 is characterized and specified for loads up to 50 pF, as confirmed in Section 9.2.1.1 of the datasheet. Driving larger capacitances is possible but may degrade switching performance - specifically increasing propagation delay and transition time beyond the 13 ns max t_pd and 8 ns max t_t values published at 6 V. For reliable timing compliance, keep total load capacitance ≤50 pF. The SN74HCS245 datasheet explicitly states this limit applies to all electrical and switching characteristics.

Does the SN74HCS245 support true bidirectional data flow on each channel?

Yes, the SN74HCS245 supports true bidirectional operation per channel via the DIR pin: when DIR = L, data flows from Port B to Port A; when DIR = H, data flows from Port A to Port B. Each channel operates independently under this control, and the OE pin globally enables or disables all outputs. This architecture is verified in the Function Table (Table 8-1) and functional description of Section 8.4. The SN74HCS245 does not require separate transmit/receive control lines per channel.

Can unused inputs on the SN74HCS245 be left floating?

No, unused inputs on the SN74HCS245 must not be left floating. Section 11.1 of the datasheet mandates termination to VCC or GND to prevent undefined logic states and increased dynamic current consumption. While Schmitt-trigger inputs tolerate slow edges, floating nodes cause unpredictable switching and elevated ICC. TI recommends 10-kΩ pull-up or pull-down resistors for unused A/B pins, as shown in Figure 8-2. Leaving inputs unconnected violates the absolute maximum ratings and risks erratic behavior in the SN74HCS245.

What is the purpose of the thermal pad on the RKS (VQFN) package of the SN74HCS245?

The thermal pad on the RKS package serves dual purposes: thermal dissipation and optional grounding. As specified in Table 5-1, it may be connected to GND to reduce junction-to-ambient thermal resistance (Rθ_JA = 75.6°C/W) or left electrically floating. It must never be connected to any signal or supply other than GND. This pad is absent in the DGS (SOT-20) variant. Proper soldering of the thermal pad is required to achieve the published thermal metrics for the SN74HCS245 RKS package.

How does the SN74HCS245 handle power-up and power-down sequencing to avoid bus contention?

To ensure high-impedance outputs during power-up/down, the datasheet (Section 8.1) specifies tying OE to VCC via a pull-up resistor - typically 10 kΩ - so OE remains high (disabled) until the supply stabilizes. This prevents unintended data leakage or bus conflicts before system initialization completes. The SN74HCS245 has no internal power-on reset; external biasing of OE is mandatory for glitch-free sequencing. This requirement directly applies to all operational modes of the SN74HCS245 and is independent of DIR state.