Texas Instruments SN74LS245NSR

Overview

SN74LS245NSR from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for asynchronous bidirectional data transfer between A and B buses in TTL-level systems. It features direction control (DIR), active-low output enable (OE), 8 ns typical propagation delay, ±15 mA high-level/24 mA low-level output drive, and hysteresis-enhanced noise immunity on bus inputs - used in industrial backplane interfaces and legacy embedded bus extension.

For engineers reviewing the SN74LS245NSR datasheet, SN74LS245NSR pinout, SN74LS245NSR application, or SN74LS245NSR equivalent, key selection considerations include its 20-pin SO package, 5 V operation, 3-state isolation capability, and compatibility with LS-TTL logic families in bus buffering, ribbon cable driving, and legacy system interconnects.

Technical Context

The SN74LS245NSR implements Schottky transistor logic (LS) with PNP input structures to reduce DC loading on shared bus lines. Its dual-bus architecture supports real-time direction reversal via DIR pin, while OE enables full 3-state isolation of both A and B ports simultaneously.

It operates strictly within 4.75–5.25 V supply range and 0–70 °C ambient temperature. Input hysteresis (0.2–0.4 V) improves noise margins on A/B bus lines, and output drive strength (–15 mA/24 mA) ensures robust signal integrity across moderate-length PCB traces or ribbon cables.

Key Specifications

Pinout & Package

SN74LS245NSR uses a 20-pin small-outline package (SO) with 12.60 mm × 5.30 mm body size, gull-wing leads, and RoHS-compliant NiPdAu plating. It is rated MSL Level-1 (unlimited floor life) and compatible with standard reflow profiles.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS245N and SN74HC245N, SN74LS245NSR delivers superior noise immunity and bus drive in space-constrained SMT layouts, making it the preferred choice for industrial backplane and ribbon cable extensions where signal fidelity and LS-TTL compatibility are mandatory.

Availability

SN74LS245NSR is available at Aetrix Electronics and suitable for industrial backplane interfaces, ribbon cable data extension, and legacy system bus expansion requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS245NSR 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 founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial, automotive, and communications reach.

SN74LS245NSR belongs to TI's legacy LS-TTL logic family, engineered specifically for robust bus interfacing in industrial control, test equipment, and retro-computing systems where compatibility, noise immunity, and predictable timing are essential.

FAQ

What is the operating voltage range for SN74LS245NSR?

The SN74LS245NSR operates strictly within 4.75 V to 5.25 V. This narrow range ensures compatibility with standard TTL logic levels and prevents marginal behavior or increased power dissipation outside specifications. Operating below 4.75 V may cause output voltage degradation or timing violations; exceeding 5.25 V risks permanent damage. Always verify VCC stability under load using a local 0.1 µF bypass capacitor near pin 20.

How does the DIR pin control data flow in SN74LS245NSR?

In SN74LS245NSR, the DIR pin determines direction: logic HIGH enables data transmission from A-side pins (2–9) to B-side pins (11–18); logic LOW reverses flow from B to A. DIR must be stable before asserting OE LOW to prevent bus contention. The function table confirms that DIR state is irrelevant when OE is HIGH, as all outputs remain in high-impedance regardless of DIR value.

Can SN74LS245NSR drive long ribbon cables reliably?

Yes - SN74LS245NSR's 24 mA sink and –15 mA source capability actively drives capacitively loaded ribbon cables up to 300 mm while maintaining signal integrity. Its hysteresis-enhanced inputs reject noise induced by crosstalk or EMI, and typical 8 ns propagation delay preserves timing margins. For best results, terminate unused channels consistently on both A and B sides and use controlled-impedance routing where possible.

What happens to the A and B buses when OE is HIGH on SN74LS245NSR?

When OE is HIGH, all eight A/B channel outputs enter high-impedance (3-state) mode, effectively isolating the A and B buses from each other. Leakage current remains below ±200 µA, preserving bus voltage levels. This isolation is critical for multi-master arbitration, hot-swap capability, and preventing contention during system reset or configuration changes - a core design feature of the SN74LS245NSR.

Is SN74LS245NSR pin-compatible with other '245-series transceivers?

SN74LS245NSR shares the industry-standard 20-pin '245 pinout across all TI variants (e.g., SN74LS245N, SN74LS245DW), including identical DIR, OE, A1–A8, B1–B8, GND, and VCC assignments. However, package dimensions, thermal characteristics, and moisture sensitivity differ - the NS package (SO) is not mechanically interchangeable with PDIP or SSOP variants without PCB redesign.