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

For engineers reviewing the SN74LS245DW datasheet, pinout, applications, or equivalent options, key selection considerations include its SOIC-20 package, 3-state isolation capability, TTL-compatible input thresholds (VIL = 0.8 V, VIH = 2 V), and drive strength suitable for driving long traces or unterminated buses.

Technical Context

The SN74LS245DW implements Schottky transistor logic (LS) with PNP inputs to reduce DC loading on shared buses and built-in hysteresis (0.2–0.4 V) on A/B-side inputs to improve noise immunity. Its DIR pin selects data flow direction (A→B or B→A), while OE enables/disables all eight channels simultaneously into high-impedance state.

It supports bidirectional communication without external timing circuitry due to synchronous internal gating, and its 3-state outputs allow direct connection to common bus lines. The device is not latch-enabled and requires no clock; operation is purely combinatorial and level-sensitive.

Key Specifications

Pinout & Package

SN74LS245DW is housed in a 20-pin SOIC (Small Outline Integrated Circuit) package measuring 12.80 mm × 7.50 mm, with gull-wing leads and surface-mount compatibility. Thermal resistance RθJA is 79.0°C/W, supporting moderate power dissipation in compact layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS245N and SN74LS245NSR, the SN74LS245DW offers a balanced trade-off: larger SOIC body than NSR for easier rework, better thermal performance than N, and full functional equivalence - making it ideal for mid-volume industrial PCBs requiring reliability and serviceability.

Availability

SN74LS245DW is available at Aetrix Electronics and suitable for industrial backplane interconnect, ribbon cable data extension, and factory automation controller applications requiring stable component supply and long-term obsolescence management.

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 with over 50 years of analog and logic IC innovation, serving industrial, automotive, and communications markets with high-reliability, widely adopted components.

The SN74LS245DW belongs to TI's legacy TTL logic portfolio, engineered specifically for robust, low-cost bidirectional bus interfacing in industrial control, test equipment, and legacy system upgrades - emphasizing pin compatibility, noise immunity, and ease of integration.

FAQ

What is the operating voltage range for SN74LS245DW?

The SN74LS245DW operates within a recommended supply voltage range of 4.75 V to 5.25 V. Operation outside this window may cause unreliable logic levels or increased power consumption. Absolute maximum VCC is 7 V, but sustained use above 5.25 V risks parametric shift or premature wear. All electrical characteristics in the datasheet - including VOH, VOL, and propagation delay - are specified at VCC = 5 V and TA = 25°C.

How does the DIR pin control data flow in SN74LS245DW?

The DIR pin on the SN74LS245DW is a level-sensitive direction control: when DIR = LOW, data flows from the B-side pins (B1–B8) to the A-side pins (A1–A8); when DIR = HIGH, data flows from A to B. This enables real-time reversal of bus traffic without latching or clocking. The SN74LS245DW does not store state - direction changes propagate through with typical 8 ns delay, and both directions are electrically identical in drive strength and timing.

Can SN74LS245DW drive a 50 Ω transmission line directly?

The SN74LS245DW can drive a 50 Ω load under defined conditions: at IOL = 24 mA, VOL ≤ 0.5 V ensures adequate low-level margin; at IOH = –15 mA, VOH ≥ 2.4 V satisfies TTL high-level requirements. However, direct 50 Ω termination may cause overshoot/ringing due to fast edges - TI recommends series termination or controlled-impedance routing. For reliable 50 Ω line driving, verify layout per SN74LS245DW application note Figure 5 and use proper bypassing.

What is the purpose of hysteresis on SN74LS245DW inputs?

Hysteresis (0.2–0.4 V) on the A and B bus inputs of the SN74LS245DW raises the effective VIH threshold when transitioning from LOW to HIGH and lowers the effective VIL threshold when transitioning from HIGH to LOW. This prevents oscillation or metastability on slow-rising or noisy signals - especially critical in ribbon cable or backplane applications where signal integrity degrades over distance. It is intrinsic to the input stage and requires no external components.

Is SN74LS245DW pin-compatible with other '245-family devices?

Yes, the SN74LS245DW shares the industry-standard '245 pinout across all TI variants (e.g., SN74LS245N, SN74LS245NSR, SN74LS245DBR). Pin 1 is DIR, pins 2–9 are A1–A8, pin 10 is GND, pins 11–18 are B8–B1 (reversed order), pin 19 is OE, and pin 20 is VCC. This allows direct substitution in existing layouts - though thermal, package, and moisture sensitivity differences (e.g., MSL rating) must be verified for new assembly processes.