Texas Instruments SN74HC640AN

Overview

SN74HC640AN from Texas Instruments is an octal inverting bus transceiver with 3-state outputs, designed for bidirectional data flow control between parallel buses in digital systems. It operates across 2V–6V supply, delivers ±4-mA output drive at 5V, exhibits typical propagation delay of 8ns (VCC = 6V, CL = 50 pF), and supports isolation via independent DIR and OE control - used in industrial backplane interfaces and legacy microcontroller bus expansion.

For engineers reviewing the SN74HC640AN datasheet, SN74HC640AN pinout, SN74HC640AN application, or SN74HC640AN equivalent, key selection criteria include its inverting logic behavior, 20-pin PDIP package compatibility, 3-state output timing under varying load capacitance (50 pF / 150 pF), and thermal performance in ambient temperatures up to +85°C.

Technical Context

The SN74HC640AN implements dual-directional data routing using a single DIR input to select A→B or B→A transfer, while OE independently enables or disables all eight channels into high-impedance state. Its CMOS architecture ensures low static current (≤80 µA ICC) and rail-to-rail output swing.

Functional modes are strictly defined by OE/DIR truth table: OE = L enables transceiver operation (DIR = L routes B→A; DIR = H routes A→B); OE = H forces all outputs to high-Z regardless of DIR. Input thresholds scale with VCC (VIH = 0.7×VCC min, VIL = 0.3×VCC max), supporting mixed-voltage system interfacing.

Key Specifications

Pinout & Package

SN74HC640AN is supplied in a 20-pin plastic dual in-line package (PDIP-N), with nominal body size 25.40 mm × 6.35 mm and 2.54 mm lead pitch. The package is through-hole mountable, RoHS-compliant, and rated for industrial temperature range.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC640AN, SN74HC245N offers polarity-consistent data transfer ideal for memory-mapped peripherals, while 74ACT640N trades supply flexibility for speed and drive strength - making SN74HC640AN optimal for mixed-voltage, cost-sensitive industrial interfaces requiring inverting logic.

Availability

SN74HC640AN is available at Aetrix Electronics and suitable for industrial backplane interfaces, microcontroller bus expansion, legacy system interfacing, and test equipment data routing requiring stable component supply and long-term obsolescence management.

Supply support for SN74HC640AN 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 solutions, with over 90 years of innovation in industrial, automotive, and communications electronics.

The SN74HC640AN belongs to TI's 74HC logic family - engineered for high noise immunity, low power, and broad voltage operation in industrial control, instrumentation, and legacy digital system upgrades.

FAQ

What is the logic function of the SN74HC640AN?

The SN74HC640AN is an inverting octal bus transceiver: data transferred from A to B or B to A is inverted at the output. This behavior is inherent to the device architecture and cannot be disabled. When DIR = H and OE = L, A inputs appear as inverted signals on B outputs; when DIR = L and OE = L, B inputs appear inverted on A outputs. The SN74HC640AN datasheet confirms this in Section 7.3 Function Table and Figure 7-1 Block Diagram.

Does the SN74HC640AN support 3.3V operation?

Yes, the SN74HC640AN fully supports 3.3V operation within its specified 2V–6V supply range. At VCC = 3.3V, it meets all recommended operating conditions: VIH = 2.31V min, VIL = 0.99V max, and delivers ≥±3.5 mA output drive. Its CMOS inputs draw ≤1 µA, ensuring compatibility with 3.3V microcontrollers and FPGAs without level translation.

What is the maximum capacitive load the SN74HC640AN can drive reliably?

The SN74HC640AN is characterized for CL = 50 pF and CL = 150 pF in its switching specifications. At CL = 150 pF and VCC = 6V, typical propagation delay is 11ns and transition time is 13ns - confirming stable operation up to 150 pF. Driving heavier loads increases delay and rise/fall times; TI recommends limiting total trace + load capacitance to ≤150 pF for timing-critical applications using SN74HC640AN.

How does the SN74HC640AN handle unused inputs?

All unused inputs on the SN74HC640AN - including DIR and OE - must be tied to a valid logic level (VCC or GND) to prevent floating states that cause excessive ICC, erratic outputs, or increased EMI. TI's SCBA004 application report mandates this practice. For example, if OE is permanently enabled, tie OE to GND; if direction is fixed, tie DIR to VCC or GND accordingly. Leaving any input unconnected violates SN74HC640AN reliability requirements.

Is the SN74HC640AN pin-compatible with other 20-pin octal transceivers?

The SN74HC640AN shares the same 20-pin PDIP footprint and signal assignment (A0–A7, B0–B7, DIR, OE, VCC, GND) with SN74HC245N and SN74HC646N, but differs in logic function: SN74HC245N is non-inverting, and SN74HC646N is inverting with latch enable. While mechanical pinout matches, functional substitution requires verification of polarity, timing, and control signal compatibility - SN74HC640AN is not a drop-in replacement without circuit-level validation.