Texas Instruments SN74HC640DWR

Overview

SN74HC640DWR from Texas Instruments is an octal inverting bus transceiver with 3-state outputs, designed for bidirectional data flow between two 8-bit buses. It operates across 2V–6V supply, delivers ±4 mA output drive at 5V, exhibits typical propagation delay of 8 ns (CL = 50 pF), and supports industrial temperature range (–40°C to +85°C). It is used in microcontroller peripheral interfacing where bus isolation and direction control are required.

For engineers reviewing the SN74HC640DWR datasheet, SN74HC640DWR pinout, SN74HC640DWR application, or SN74HC640DWR equivalent, key selection considerations include its inverting logic behavior, dual-control (DIR/OE) architecture, SOIC-20 package compatibility, and 3-state output timing under varying load and voltage conditions.

Technical Context

The SN74HC640DWR implements an octal bidirectional transceiver with independent direction (DIR) and output-enable (OE) inputs controlling all eight channels simultaneously. Its inverting logic means A→B and B→A data paths invert signal polarity, requiring system-level logic compensation.

It uses standard HC CMOS technology with rail-to-rail output swing, low input current (≤1 µA), and high-current 3-state outputs capable of driving up to 10 LSTTL loads. Thermal resistance is 58°C/W (R_θJA) in the DW package, supporting stable operation under continuous bus loading.

Key Specifications

Pinout & Package

SN74HC640DWR is housed in a 20-pin SOIC (DW) package measuring 12.80 mm × 7.50 mm with maximum height of 2.65 mm, RoHS-compliant NiPdAu lead finish, and moisture sensitivity level 1 (260°C reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC640DWR, SN74HCT640DWR offers TTL-compatible inputs for legacy integration, while 74LCX640MTCX provides superior speed and 3.3 V efficiency at the cost of pinout incompatibility - making SN74HC640DWR the optimal choice for general-purpose 2–6 V industrial bus bridging where design reuse and SOIC manufacturability are critical.

Availability

SN74HC640DWR is available at Aetrix Electronics and suitable for industrial PLC backplanes, microcontroller expansion buses, and automated test fixture data routing requiring stable component supply, long-term lifecycle support, and RoHS-compliant SOIC packaging.

Supply support for SN74HC640DWR 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 specializing in analog, embedded processing, and logic ICs, with over 50 years of innovation in industrial, automotive, and communications markets.

The SN74HC640DWR belongs to TI's 74HC logic family - engineered for high noise immunity, low power consumption, and seamless interoperability across mixed-voltage digital systems in harsh industrial environments.

FAQ

What is the logic polarity of SN74HC640DWR?

The SN74HC640DWR implements inverting logic: data transferred from A to B or B to A is logically inverted. This behavior is inherent to the device architecture and must be accounted for in firmware or upstream logic design. The SN74HC640DWR datasheet confirms inversion in Section 7.3 Function Table and Figure 7-1 Block Diagram. No external inversion is needed - the inversion is consistent and deterministic across all eight channels.

Can SN74HC640DWR operate at 3.3 V supply?

Yes, SN74HC640DWR is fully specified for operation from 2 V to 6 V, including 3.3 V nominal supply. At V_CC = 3.3 V, it delivers ≥3.15 V VOH (min) and ≤0.1 V VOL (max) under 6 mA load, meeting standard 3.3 V LVTTL thresholds. The SN74HC640DWR maintains t_pd ≤ 18 ns (typical) at this voltage, supporting reliable timing in mixed-voltage embedded systems.

What is the recommended bypass capacitor for SN74HC640DWR?

Texas Instruments recommends a 0.1 µF ceramic capacitor placed as close as possible to Pin 20 (V_CC) and Pin 10 (GND) of the SN74HC640DWR. This minimizes high-frequency supply noise and stabilizes transient current demands during output switching. For enhanced noise suppression, a parallel 1 µF capacitor may be added - but the 0.1 µF unit is mandatory per TI's layout guidelines in Section 8 of the SN74HC640DWR datasheet.

Does SN74HC640DWR support hot-swap or live-insertion?

SN74HC640DWR supports controlled hot-swap via its 3-state outputs: asserting OE = HIGH places all A/B pins in high-impedance mode before physical insertion, preventing bus contention. However, it lacks built-in hot-swap protection circuitry (e.g., slew-rate limiting or current limiting), so external current-limiting resistors or dedicated hot-swap controllers are recommended for repeated live-insertion in high-reliability systems using SN74HC640DWR.

How does the DIR and OE pin interaction affect bus behavior in SN74HC640DWR?

In SN74HC640DWR, DIR controls data direction (A↔B), while OE independently enables/disables all outputs. When OE = HIGH, outputs are high-impedance regardless of DIR state - fully isolating both buses. When OE = LOW, DIR determines flow direction: DIR = LOW routes B→A; DIR = HIGH routes A→B. This separation allows safe bus arbitration, e.g., holding OE HIGH during direction changes to avoid glitches. This dual-control behavior is explicitly defined in Table 7-1 of the SN74HC640DWR datasheet.