Texas Instruments SN74HC640NS

Overview

SN74HC640NS from Texas Instruments is an octal inverting bus transceiver with 3-state outputs, designed for bidirectional data flow control between two 8-bit buses. It features direction control (DIR), active-low output enable (OE), propagation delay of 9 ns at 5 V, bus-driver output capability, and operates across 2–6 V supply range.

For engineers reviewing the SN74HC640NS datasheet, SN74HC640NS pinout, SN74HC640NS application, or SN74HC640NS equivalent, key selection criteria include inverting logic behavior, 3-state isolation timing (tPZH/tPHZ ≤ 45 ns), voltage-level compatibility with TTL and CMOS systems, and NS package thermal and routing constraints.

Technical Context

The SN74HC640NS implements dual-directional data transfer using a single DIR input to select A→B (DIR = LOW) or B→A (DIR = HIGH), with all outputs inverted relative to inputs. Its 3-state control is asserted by active-low OE, enabling bus sharing without contention.

It belongs to the 74HC high-speed CMOS logic family, compliant with JEDEC Std 7A, and offers TTL-compatible input thresholds in HCT variants-though SN74HC640NS is the HC version with CMOS input thresholds (VI = GND to VCC).

Key Specifications

Pinout & Package

SN74HC640NS is supplied in a 20-pin plastic DIP (Dual In-line Package) with 0.3-inch body width and through-hole mounting. Pin 1 is marked with a notch or dot; pins are numbered counter-clockwise from top-left.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC640NS, SN74HCT640N improves input compatibility with legacy TTL but shares identical functionality and layout; 74AC640PC trades power efficiency and noise margin for raw speed - making SN74HC640NS optimal for general-purpose, low-noise, mixed-voltage industrial bus extension.

Availability

SN74HC640NS is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy microprocessor bus extensions, and automated test fixture designs requiring stable component supply, long-lifecycle support, and through-hole assembly compatibility.

Supply support for SN74HC640NS 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 broad industrial and automotive qualification.

The SN74HC640NS belongs to TI's 74HC logic portfolio, engineered for reliable, low-power, pin-compatible upgrades of obsolete TTL bus interface ICs in long-lifecycle equipment.

FAQ

What logic family does the SN74HC640NS belong to, and how does it differ from SN74HCT640N?

The SN74HC640NS belongs to the 74HC high-speed CMOS logic family, featuring CMOS-input thresholds (VI = GND to VCC). In contrast, SN74HCT640N uses TTL-compatible inputs (VIH ≥ 2.0 V), allowing direct interfacing with 74LS devices. Both share identical pinout, function, and AC specs-but SN74HC640NS draws less quiescent current and offers better noise immunity in purely CMOS systems.

Does the SN74HC640NS support 3.3 V operation, and what are the timing implications?

Yes, SN74HC640NS operates from 2 V to 6 V, including 3.3 V. At VCC = 3.3 V, propagation delay increases to ~15 ns (max) and 3-state timing extends to ~60 ns (max), per AC characterization curves. System timing budgets must account for this derating versus 5 V operation, especially in high-speed bus applications.

How is data inversion implemented in the SN74HC640NS, and does it affect both directions?

Data inversion in SN74HC640NS is inherent to its logic design: all outputs (A0–A7 and B0–B7) are inverted relative to their corresponding inputs, regardless of DIR state. When DIR = LOW (A→B), Bn = NOT(An); when DIR = HIGH (B→A), An = NOT(Bn). This symmetrical inversion is fixed and cannot be disabled.

Can the SN74HC640NS replace the SN74LS640 in an existing design without modifications?

Yes - SN74HC640NS is pin-compatible and functionally equivalent to SN74LS640, with identical pinout, DIR/OE control, and inverting 3-state behavior. However, due to CMOS input structure, it requires no pull-up resistors on unused inputs and draws significantly less supply current, simplifying power design.

What is the maximum capacitive load the SN74HC640NS can drive while maintaining specified timing?

SN74HC640NS is characterized for CL = 15 pF (propagation delay) and CL = 50 pF (full AC specs). Driving loads beyond 50 pF will increase propagation and transition times nonlinearly. For reliable 9 ns timing, keep total net capacitance ≤15 pF; for guaranteed AC performance across temperature, limit to 50 pF with proper termination and layout.