Texas Instruments SN74HC640N

Overview

SN74HC640N from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for bidirectional data transfer between two 8-bit buses in asynchronous systems. It features inverting logic, operates from 2V to 6V, delivers ±4 mA output drive at 5V, and exhibits typical propagation delay of 8 ns (VCC = 6 V, CL = 50 pF). It is commonly used in microcontroller peripheral interfacing and legacy bus isolation.

For engineers reviewing the SN74HC640N datasheet, SN74HC640N pinout, SN74HC640N application, or SN74HC640N equivalent, key selection criteria include its 3-state control architecture (DIR/OE), PDIP-20 package compatibility with through-hole prototyping, guaranteed 10 LSTTL load drive capability, and -40°C to +85°C industrial temperature range.

Technical Context

The SN74HC640N implements eight independent inverting transceiver channels, each controlled by a shared direction (DIR) input and global output-enable (OE) signal. Its functional modes-A-to-B, B-to-A, and high-impedance isolation-are defined by the DIR/OE truth table, with no internal latching or clocking.

It uses standard HC CMOS process technology, delivering low static current (≤80 µA ICC max), high noise immunity (VIH/VIL thresholds scale with VCC), and robust ESD protection per JEDEC JS-001. All inputs tolerate slow or floating conditions only when actively terminated to VCC/GND per TI SCBA004 guidelines.

Key Specifications

Pinout & Package

SN74HC640N is housed in a 20-pin Plastic Dual In-line Package (PDIP), measuring 25.40 mm × 6.35 mm (1.00" × 0.25"), with 0.1" lead pitch and through-hole mounting. The package includes integrated cavity for mechanical stability and meets JEDEC MS-001 standards.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC640N, SN74HCT640N offers superior noise immunity in mixed-logic environments but shares identical functionality and PDIP-20 packaging, whereas 74LCX640M delivers faster performance at lower voltage but requires layout changes due to incompatible footprint and lack of 5 V tolerance.

Availability

SN74HC640N is available at Aetrix Electronics and suitable for industrial control systems, test instrumentation, and legacy microcontroller interface designs requiring stable component supply and long-term obsolescence management.

Supply support for SN74HC640N 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 U.S.-based semiconductor company specializing in analog, embedded processing, and logic solutions, with over 90 years of innovation in industrial, automotive, and communications markets.

The SN74HC640N belongs to TI's industry-standard 74HC logic family, engineered for robustness, wide supply flexibility, and seamless integration into legacy and mixed-voltage digital systems.

FAQ

What is the maximum operating frequency supported by SN74HC640N?

The SN74HC640N does not specify a maximum clock frequency because it is an asynchronous transceiver with no internal clock. Its usable data rate depends on propagation delay (tpd ≤ 27 ns max at VCC = 6 V, CL = 150 pF) and system timing margins. For reliable bus handshaking, designers typically limit toggle rates to ≤10 MHz in heavily loaded configurations. The SN74HC640N itself imposes no hard frequency ceiling beyond what its tpd and transition times allow.

Can SN74HC640N operate reliably at 3.3 V supply voltage?

Yes, SN74HC640N is fully specified for operation at 3.3 V, with recommended operating conditions confirming VCC = 2 V to 6 V. At 3.3 V, it delivers ±4 mA output drive, maintains VIH ≥ 2.31 V and VIL ≤ 0.99 V, and achieves typical tpd = 10 ns (CL = 50 pF). This makes SN74HC640N suitable for direct interfacing between 3.3 V MCUs and 5 V peripherals when used with appropriate level-aware control signals.

Is SN74HC640N pin-compatible with SN74LS640N?

No, SN74HC640N is not pin-compatible with SN74LS640N. Although both are octal transceivers in PDIP-20 packages, their pin assignments differ: SN74LS640N places GND at Pin 10 and VCC at Pin 20, while SN74HC640N uses Pin 9 for GND and Pin 10 for VCC. Swapping them will cause immediate power shorting. Always verify pinouts using official TI SCLS303E and TI SN74LS640 datasheets before substitution.

Does SN74HC640N require external pull-up or pull-down resistors on DIR and OE pins?

SN74HC640N does not require external pull-up or pull-down resistors on DIR or OE if those signals are actively driven by a microcontroller or FPGA. However, TI mandates that all unused inputs-including DIR and OE-must be held at valid logic levels (VCC or GND) to prevent undefined states and excessive current draw. Leaving either pin floating violates the Absolute Maximum Ratings and may cause erratic bus behavior or increased ICC.

What thermal considerations apply to SN74HC640N in continuous operation?

SN74HC640N has a junction-to-ambient thermal resistance (RθJA) of 69°C/W in its PDIP-20 package. At maximum rated ICC (80 µA) and worst-case output loading, self-heating is negligible (<1°C rise). However, under sustained 3-state switching at high frequency and capacitive load, power dissipation rises via Cpd × VCC² × f. For ambient temperatures approaching +85°C, ensure board-level airflow or copper pour to maintain TJ < 125°C, especially when driving >50 pF loads at >1 MHz.