Texas Instruments SN74ALS645ANSR

Overview

SN74ALS645ANSR 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-compatible systems. It features direction control (DIR), output enable (OE), ±24 mA low-level drive capability, 0°C to 70°C operating range, and SOP-20 package. It is used in legacy industrial backplane interfaces requiring bus isolation and level translation.

For engineers reviewing the SN74ALS645ANSR datasheet, SN74ALS645ANSR pinout, SN74ALS645ANSR application, or SN74ALS645ANSR equivalent, this page delivers verified electrical specs, validated SOP-20 pin mapping, real-world bus isolation use cases, and two confirmed alternative parts with documented functional and thermal differences.

Technical Context

This device implements true TTL logic with active-low 3-state control, enabling bidirectional data flow via DIR input and bus isolation via OE. Its propagation delays (tPLH/tPHL ≤ 10 ns) and enable/disable times (tPZH/tPLZ ≤ 20 ns) are specified under 50 pF load and 500 Ω source termination.

The SN74ALS645ANSR operates at VCC = 4.5–5.5 V with VIH ≥ 2 V and VIL ≤ 0.8 V, delivering VOH ≥ 2.4 V at IOH = –12 mA and VOL ≤ 0.4 V at IOL = 24 mA - meeting standard ALS family voltage thresholds and drive strength.

Key Specifications

Pinout & Package

SOP-20 (NS) package: 20-pin small-outline plastic package with gull-wing leads, 1.27 mm pitch, 8.4 mm × 13.0 mm body, 2.65 mm max height, RoHS-compliant NiPdAu lead finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ALS645ANSR, SN74ALS645AN offers identical logic behavior but lacks RoHS compliance and SMT compatibility, while SN74AS645N trades power efficiency for speed and drive strength - making each suitable only for distinct mechanical, thermal, or timing constraints.

Availability

SN74ALS645ANSR is available at Aetrix Electronics and suitable for industrial control systems, legacy test equipment, and microcontroller peripheral interfacing requiring stable component supply, long-term obsolescence mitigation, and RoHS-compliant SOP packaging.

Supply support for SN74ALS645ANSR 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 for industrial, automotive, and communications markets.

The SN74ALS645ANSR belongs to TI's legacy 74ALS logic family, engineered for robustness in noise-prone industrial environments and backward compatibility with decades-old TTL-based designs.

FAQ

What is the maximum recommended operating voltage for SN74ALS645ANSR?

The absolute maximum supply voltage for SN74ALS645ANSR is 7 V, but the recommended operating range is strictly 4.5 V to 5.5 V. Operation outside this window risks violating input/output voltage thresholds and may cause unreliable 3-state behavior or accelerated parametric drift. Always maintain VCC within 4.75–5.25 V for optimal performance and longevity of the SN74ALS645ANSR.

Does SN74ALS645ANSR support hot-swapping on live buses?

SN74ALS645ANSR supports controlled hot-swap operation only when OE is asserted high before insertion to place all I/Os in high-impedance state. Its 3-state outputs prevent bus contention, but the device itself lacks built-in bus-fault protection or slew-rate control. System-level design - including series resistors, TVS diodes, and sequencing - remains essential for safe live insertion of the SN74ALS645ANSR.

Can SN74ALS645ANSR interface directly with CMOS logic?

SN74ALS645ANSR can drive standard CMOS inputs (e.g., 74HC, 74AC) under 5 V supply, as its VOH ≥ 2.4 V meets HC/AC VIH(min) requirements. However, CMOS outputs driving SN74ALS645ANSR inputs must meet ALS VIL ≤ 0.8 V and VIH ≥ 2.0 V - which excludes older 4000-series CMOS but works with 74HC outputs. Verify level compatibility per signal path when integrating SN74ALS645ANSR into mixed-logic systems.

What is the thermal resistance (θJA) of the SN74ALS645ANSR in its SOP-20 package?

The published junction-to-ambient thermal resistance (θJA) for SN74ALS645ANSR in the SOP-20 (NS) package is 110°C/W under JEDEC JESD51-7 standard conditions (single-layer board, 1 in² copper). This value assumes no internal heatsinking; actual θJA improves to ~65°C/W with 2 oz copper and thermal vias. Thermal derating is required above 55°C ambient when ICC exceeds 45 mA - critical for sustained operation of the SN74ALS645ANSR.

Is there a pin-compatible drop-in replacement for SN74ALS645ANSR with extended temperature range?

No pin-compatible drop-in replacement exists for SN74ALS645ANSR with extended temperature range. The military-grade SN54ALS645AJ uses CDIP-20 packaging and operates from –55°C to 125°C, but it is not pin-compatible due to different package type, lead pitch, and mounting method. Migration would require PCB redesign. For extended temp needs, SN74ALS645ANSR must be replaced with a functionally equivalent but mechanically distinct part - not a direct substitute.