Texas Instruments SN74LS640DB

Overview

SN74LS640DB from Renesas Electronics is an octal bus transceiver with inverted 3-state outputs, designed for asynchronous bidirectional data transfer between two 8-bit buses. It features direction control (DIR) and output enable (G), operates at 5 V supply, supports ±15 mA output drive, and delivers propagation delays as low as 6 ns. It is used in legacy industrial control backplanes and TTL-compatible system interconnects.

For engineers reviewing the SN74LS640DB datasheet, SN74LS640DB pinout, SN74LS640DB application, or SN74LS640DB equivalent, key selection criteria include its inverted output logic, 3-state isolation behavior, DIR/G dual-control architecture, and compatibility with LS-TTL voltage thresholds and timing budgets in bus arbitration circuits.

Technical Context

The SN74LS640DB implements eight identical bidirectional transceiver cells, each with complementary output inversion and independent 3-state control gated by DIR and G inputs. Its logic function strictly follows the truth table: when G = L, data flows A→B if DIR = H or B→A if DIR = L; when G = H, all outputs enter high-impedance state regardless of DIR.

It uses standard bipolar LS-TTL process technology, with input thresholds VIH = 2.0 V (min) and VIL = 0.8 V (max), output VOH = 2.4 V (min) at –3 mA, and VOL = 0.4 V (max) at 12 mA. Propagation delays are asymmetric: tPLH/tPHL = 6–15 ns depending on direction and load, and enable/disable times range from 15 to 40 ns under CL = 45 pF.

Key Specifications

Pinout & Package

SN74LS640DB is housed in a 20-pin SOIC package (JEITA SOP-20, Renesas code FP-20DAV), measuring 7.5 mm × 12.6 mm with 1.27 mm pitch. The package features Ni/Pd/Au plating and is rated for reflow soldering per J-STD-020.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS640DB, SN74LS245N offers identical mechanical and timing compatibility but lacks output inversion, while 74ACT245SCX provides superior speed and drive efficiency at the cost of LS-TTL voltage threshold alignment - making SN74LS640DB uniquely suited for drop-in replacement in legacy inverted-bus architectures.

Availability

SN74LS640DB is available at Aetrix Electronics and suitable for industrial backplane interconnect, legacy CPU bus extension, and automated manufacturing controller applications requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS640DB 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

Renesas Electronics Corporation is a global semiconductor leader delivering microcontrollers, analog, power, and connectivity solutions for industrial, automotive, and infrastructure markets.

The HD74LS640 product line was developed by Renesas (formerly NEC Electronics) to provide pin- and function-compatible replacements for legacy 74LS-series bus transceivers in industrial control and instrumentation systems.

FAQ

What is the logic polarity of SN74LS640DB outputs?

The SN74LS640DB features inverted 3-state outputs: data appearing on the A or B bus is logically complemented relative to the source. This inversion is inherent to the device's internal gate structure and applies regardless of direction (A→B or B→A). Designers must account for this in bus protocol layer logic or use external inverters if true non-inverted transfer is required. The SN74LS640DB datasheet confirms this behavior in both the block diagram and function table.

Does SN74LS640DB support hot-swap or live-insertion?

No, SN74LS640DB does not support hot-swap operation. Its bipolar LS-TTL process lacks bus-hold, power-up 3-state, or current-limiting features required for safe live insertion. Applying VCC or signals before both power rails stabilize may cause latch-up or excessive current draw. For SN74LS640DB integration in modular systems, power sequencing and mechanical interlocks must ensure VCC is stable and G is held high before signal assertion.

What is the maximum capacitive load SN74LS640DB can drive reliably?

SN74LS640DB is characterized up to CL = 45 pF in its switching specifications, with propagation and enable times guaranteed under that load. Driving >45 pF may increase propagation delay beyond 15 ns and degrade edge rates, risking setup/hold violations in high-speed interfaces. For heavier loads, SN74LS640DB should be paired with a buffer or distributed via shorter traces; the datasheet specifies RL = 667 Ω and CL = 45 pF as the test condition for all timing parameters.

Can SN74LS640DB operate at 3.3 V supply?

No, SN74LS640DB is specified only for 4.75–5.25 V operation. Its bipolar LS-TTL input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and output drive strength depend on 5 V VCC. At 3.3 V, input recognition fails (VIH requirement unmet), output VOH drops below 2.0 V, and sink/source capability degrades significantly. Using SN74LS640DB at 3.3 V violates Absolute Maximum Ratings and risks functional failure or increased ICCZ leakage.

Is SN74LS640DB RoHS compliant?

Yes, SN74LS640DB is RoHS compliant. Renesas Electronics confirms compliance with EU Directive 2011/65/EU (RoHS 2) for all currently supplied lots, including lead-free terminations (Ni/Pd/Au plating) and halogen-free molding compound. The RoHS status is documented in Renesas' official environmental reports and applies to the FP-20DAV (SOIC-20) package variant of SN74LS640DB.