Texas Instruments SN74LS245N

Overview

SN74LS245N 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 temperature range - commonly used in industrial backplane and ribbon cable interconnects.

For engineers reviewing the SN74LS245N datasheet, SN74LS245N pinout, SN74LS245N application, or SN74LS245N equivalent, key selection considerations include its PDIP-20 package, TTL-compatible input thresholds (VIH = 2 V, VIL = 0.8 V), 3-state isolation capability, and legacy LS logic timing behavior in bus buffering and level-shifting contexts.

Technical Context

The SN74LS245N implements Schottky transistor–transistor logic (TTL) with PNP inputs to reduce DC bus loading and built-in hysteresis on A/B-side inputs to improve noise immunity. Its DIR pin selects data flow direction (A→B or B→A), while OE enables or disables all eight channels simultaneously into high-impedance state.

It supports bidirectional communication without external latching, uses standard '245 pinout, and delivers 24 mA sink / –15 mA source drive per channel under recommended operating conditions (VCC = 4.75–5.25 V). Propagation delay is tightly specified at 8–12 ns (tPLH/tPHL) with 25–40 ns enable/disable times.

Key Specifications

Pinout & Package

SN74LS245N is housed in a 20-pin plastic dual in-line package (PDIP) with 24.33 mm × 6.35 mm body size and through-hole mounting. Pin 10 is GND, pin 20 is VCC, and all I/O pins are arranged symmetrically for A-side (pins 2–9) and B-side (pins 11–18), with DIR (pin 1) and OE (pin 19) as dedicated controls.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ALS245N and SN74F245N, the SN74LS245N offers optimal balance of drive strength, noise immunity, and power efficiency for legacy 5 V systems - making it preferred for industrial retrofit, test equipment repair, and cost-sensitive embedded bus extensions where strict timing margins are not dominant.

Availability

SN74LS245N is available at Aetrix Electronics and suitable for industrial backplane interconnect, ribbon cable data links, legacy test equipment interfaces, and factory PLC module expansion requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS245N 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 founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial and automotive portfolio coverage.

The SN74LS245N belongs to TI's legacy TTL logic family, engineered specifically for robust, low-cost bidirectional bus interfacing in 5 V systems - emphasizing reliability, noise immunity, and backward compatibility over raw speed.

FAQ

What is the maximum operating voltage for SN74LS245N?

The SN74LS245N has an absolute maximum supply voltage of 7 V, but its recommended operating range is strictly 4.75 V to 5.25 V. Operating outside this window risks parametric shift or permanent damage. The device is optimized for stable 5 V rails, and TI specifies electrical characteristics only within the recommended range - so SN74LS245N must not be used with unregulated or poorly filtered 5.5 V supplies.

Does SN74LS245N support hot-swapping on a live bus?

SN74LS245N does not support true hot-swap operation due to lack of bus-fault protection or power-on reset circuitry. However, its 3-state outputs allow safe insertion/removal when OE is held high (disabled) and DIR is stable before power application. TI recommends sequencing VCC before applying signals and using current-limiting resistors on A/B lines - critical for avoiding latch-up during SN74LS245N insertion into an energized bus.

Can SN74LS245N interface directly with CMOS logic?

SN74LS245N can drive standard CMOS inputs (e.g., 74HCxx) only with external pull-up resistors on B-side outputs, because its VOH (min 2.4 V at –3 mA) falls below the 3.5 V VIH threshold of 5 V CMOS. Direct connection to CMOS may cause logic errors. For reliable interfacing, use SN74LS245N into TTL or LS-family devices - or add level-shifting circuitry when connecting to CMOS. The SN74LS245N datasheet confirms compatibility only with TTL-level loads.

What is the purpose of hysteresis in SN74LS245N inputs?

The SN74LS245N incorporates 0.2–0.4 V input hysteresis on A and B bus pins to widen the noise margin against voltage fluctuations caused by ground bounce, crosstalk, or EMI on shared traces. This design feature prevents false triggering during slow-rising or noisy signals - especially beneficial in factory automation or test equipment where long cables and mixed-signal environments are common. Hysteresis is intrinsic to the LS process and requires no external components to function.

How should unused channels of SN74LS245N be terminated?

Unused SN74LS245N channels must be terminated on both A and B sides to the same logic level (VCC or GND) to prevent floating inputs, which can cause excessive ICC or oscillation. TI explicitly warns against tying A4 to VCC and B4 to GND - this creates unintended current paths. For permanently enabled devices, tie OE low and terminate unused pairs consistently; for isolated operation, hold OE high and terminate all unused A/B pins to GND. Proper termination ensures stable SN74LS245N operation and avoids thermal overstress.