Texas Instruments SN74LS245DWR

Overview

SN74LS245DWR 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 expansion.

For engineers reviewing the SN74LS245DWR datasheet, SN74LS245DWR pinout, SN74LS245DWR application, or SN74LS245DWR equivalent, key selection criteria include 5 V operation, SOIC-20 package compatibility, bidirectional bus isolation capability, 3-state output timing margins, and legacy TTL logic family interoperability in retrofit and maintenance designs.

Technical Context

The SN74LS245DWR implements Schottky transistor–transistor logic (TTL) with PNP input stages to reduce DC loading on shared bus lines. 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 operates within 4.75 V to 5.25 V supply range at 0 °C to 70 °C ambient, delivering VOH ≥ 2.4 V at –15 mA and VOL ≤ 0.5 V at 24 mA. Input hysteresis (0.2–0.4 V) improves noise rejection on A/B bus lines, and propagation delays (tPLH/tPHL = 8–12 ns) support reliable timing in synchronous and asynchronous bus architectures.

Key Specifications

Pinout & Package

SN74LS245DWR is housed in a 20-pin SOIC (DW) package measuring 12.80 mm × 7.50 mm, with standard 0.300-inch body width and 1.27 mm pitch. The package supports surface-mount reflow assembly per Level-1-260°C-MSL rating.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS245N and SN74ALS245N, SN74LS245DWR offers optimal balance of surface-mount compatibility, commercial temperature range, RoHS compliance, and proven field reliability - making it the preferred choice for new production runs of industrial control hardware.

Availability

SN74LS245DWR is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus expansion, and ribbon cable signal integrity applications requiring stable component supply and long-term lifecycle support.

Supply support for SN74LS245DWR 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, automotive, and communications portfolio coverage.

SN74LS245DWR belongs to TI's legacy 74LS logic family, engineered for robustness, interoperability, and backward compatibility in industrial control, test equipment, and automation infrastructure.

FAQ

What is the maximum operating supply voltage for SN74LS245DWR?

The absolute maximum supply voltage for SN74LS245DWR is 7 V, but its recommended operating range is strictly 4.75 V to 5.25 V per TI's datasheet. Operating outside this window risks violating output voltage specifications (VOH/VOL), increasing ICC, or causing premature wear. Always use a regulated 5 V source with local 0.1 µF bypass capacitance at the VCC pin of SN74LS245DWR to ensure stability.

Does SN74LS245DWR support bidirectional data flow on all eight channels simultaneously?

Yes, SN74LS245DWR supports simultaneous bidirectional flow across all eight channels - but direction is unified per DIR pin state: when DIR = HIGH, data flows A→B; when DIR = LOW, data flows B→A. Each channel (A1↔B1 through A8↔B8) operates synchronously under this control, with no per-channel direction select. All channels share the same OE and DIR inputs.

Can SN74LS245DWR be used in place of SN74LS244 or SN74LS240?

No - SN74LS245DWR is not functionally interchangeable with SN74LS244 (octal buffer, unidirectional) or SN74LS240 (octal inverter buffer, unidirectional). SN74LS245DWR provides bidirectional transceiver capability with DIR and OE controls, whereas SN74LS244/SN74LS240 lack direction control and have fixed input/output assignments. Substitution would require PCB redesign and firmware logic changes.

What is the thermal resistance (RθJA) of SN74LS245DWR in its SOIC-20 package?

The junction-to-ambient thermal resistance (RθJA) for SN74LS245DWR in the SOIC-20 (DW) package is 79.0 °C/W, as specified in TI's SDLS146B datasheet Section 7.4. This value assumes standard JEDEC 2-layer board conditions. For sustained 24 mA per output operation, derating calculations show safe continuous power dissipation up to ~350 mW at 25 °C ambient - verify board copper area and airflow if operating near thermal limits.

How does the hysteresis feature of SN74LS245DWR improve noise immunity?

SN74LS245DWR incorporates 0.2–0.4 V of input hysteresis (VT+ – VT–) on all A and B bus pins. This means the rising-edge threshold (VT+) is ~0.3 V higher than the falling-edge threshold (VT–), preventing oscillation or false triggering during slow or noisy transitions - especially critical in electrically noisy factory environments or long cable runs where ground bounce or EMI can distort edges. This design directly enhances reliability without external RC filtering.