Texas Instruments SN74LS245DW

Overview

SN74LS245DW 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 operates at 5 V with 0°C to 70°C industrial temperature range - used in backplane interconnects and ribbon-cable-driven industrial controllers.

For engineers reviewing the SN74LS245DW datasheet, SN74LS245DW pinout, SN74LS245DW application, or SN74LS245DW equivalent, key selection criteria include 3-state isolation capability, bidirectional DIR-controlled flow, TTL-compatible input thresholds (VIH = 2 V, VIL = 0.8 V), and SOIC-20 package thermal resistance (RθJA = 79.0°C/W) for board-level thermal design.

Technical Context

The SN74LS245DW implements Schottky transistor logic (LS-TTL) with PNP inputs to reduce DC bus loading and built-in hysteresis (0.2–0.4 V) on all A/B-side inputs to improve noise immunity. Its functional modes are fully defined by DIR (A→B when HIGH, B→A when LOW) and OE (all outputs disabled when HIGH).

It supports true bidirectional bus isolation: when OE is HIGH, all 16 I/O pins enter high-impedance state regardless of DIR state; when OE is LOW, data flows per DIR polarity with simultaneous 8-channel operation and no internal contention. Propagation delays (tPLH/tPHL = 8–12 ns) and enable/disable times (tPZL/tPLZ = 15–40 ns) are specified at CL = 45 pF and RL = 667 Ω.

Key Specifications

Pinout & Package

SN74LS245DW is housed in a 20-pin SOIC (Small Outline Integrated Circuit) package with 12.80 mm × 7.50 mm body size, gull-wing leads, and surface-mount footprint compatible with standard reflow profiles (MSL Level-1).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS245N and SN74ALS245N, the SN74LS245DW offers SOIC-20 surface-mount compatibility with moderate thermal performance (79.0°C/W), making it optimal for space-constrained industrial PCBs where legacy LS-speed operation suffices and reflow assembly is preferred.

Availability

SN74LS245DW is available at Aetrix Electronics and suitable for industrial backplane interconnects, legacy MCU bus extensions, and building automation controller hubs requiring stable component supply across extended product lifecycles.

Supply support for SN74LS245DW 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 delivering analog, embedded processing, and connectivity solutions with emphasis on reliability, longevity, and industrial-grade qualification.

The SN74LS245DW belongs to TI's legacy 74LS logic family, engineered for robustness in industrial control, test equipment, and infrastructure systems where interoperability with decades-old TTL designs remains critical.

FAQ

What is the maximum operating temperature for the SN74LS245DW?

The SN74LS245DW is rated for an operating free-air temperature range of 0°C to 70°C. This industrial-grade specification ensures stable performance in commercial and non-automotive embedded environments. Exceeding 70°C may cause parameter drift in propagation delay, output voltage levels, and increased leakage current - thermal derating is required above this limit per its RθJA = 79.0°C/W rating.

Does the SN74LS245DW support bidirectional data flow without external logic?

Yes, the SN74LS245DW natively supports bidirectional data flow using only its DIR pin: when DIR = HIGH, data transfers from A-side inputs to B-side outputs; when DIR = LOW, data flows from B-side to A-side. No external gates or sequencing logic are needed - the internal architecture handles full 8-channel reversal synchronously with DIR edge transitions.

Can the SN74LS245DW drive a 50 Ω transmission line directly?

The SN74LS245DW can drive a 50 Ω load transiently but is not optimized for controlled-impedance line driving. Its 24 mA low-level output current delivers ~1.2 V into 50 Ω (V = I × R), below TTL VOH/VOL specs. For reliable 50 Ω termination, use series resistors (e.g., 33 Ω) or dedicated line drivers - the SN74LS245DW excels at driving unterminated buses or fan-out to multiple LS inputs.

Is the SN74LS245DW pin-compatible with other '245 transceivers?

Yes, the SN74LS245DW uses the industry-standard '245 pinout: DIR on pin 1, A1–A8 on pins 2–9, GND on pin 10, B8–B1 on pins 11–18, OE on pin 19, and VCC on pin 20. This matches SN74ALS245, SN74F245, and SN74HC245 (with appropriate voltage translation), enabling direct PCB replacement where logic family constraints allow.

What happens to the A and B buses when OE is HIGH on the SN74LS245DW?

When OE is HIGH on the SN74LS245DW, all 16 I/O pins (A1–A8 and B1–B8) enter high-impedance (3-state) mode regardless of DIR state or input activity. This electrically isolates the A and B buses, preventing signal coupling, power backfeed, or contention - a critical feature for bus arbitration, hot-swap capability, and multi-drop system partitioning.