Texas Instruments SN74AS240ANSR

Overview

SN74AS240ANSR from Texas Instruments is an octal noninverting buffer/driver with 3-state outputs, designed for memory address driving, bus interfacing, and clock distribution in TTL-compatible systems. It operates at 4.5–5.5 V, delivers 64 mA low-level output current, features 6.5 ns typical propagation delay (A→Y), and uses pnp input circuitry to reduce DC loading on upstream logic.

For engineers reviewing the SN74AS240ANSR datasheet, SN74AS240ANSR pinout, SN74AS240ANSR application, or SN74AS240ANSR equivalent, this page provides verified functional specifications, SOP-20 package details, real-world use cases in bus buffering and address register isolation, and validated alternative parts for design continuity.

Technical Context

The SN74AS240ANSR implements dual 4-bit noninverting buffers with independent active-low 3-state enable inputs (1OE, 2OE). Each buffer pair drives one of two 4-bit output groups (Y1–Y4 and Y1'–Y4'), supporting bidirectional bus control when paired with complementary devices like SN74AS241A.

Its AS-family architecture delivers faster switching than ALS variants: tPLH/tPHL ≤ 6.5 ns at VCC = 5 V, CL = 50 pF, with symmetrical enable/disable timing (tPZH/tPLZ ≤ 9 ns) and high noise immunity via Schmitt-trigger-like input thresholds (VIL = 0.8 V, VIH = 2 V).

Key Specifications

Pinout & Package

SOP-20 (NS) package: 20-pin small-outline plastic package, 0.65 mm lead pitch, 7.5 × 12.6 mm body, 2.0 mm max height, RoHS-compliant NiPdAu lead finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal 3-state buffer applications.

Compared with SN74ALS240ANSR, SN74AS240ANSR delivers 2.7× stronger drive and 30% faster timing at modestly higher ICC; versus SN74AS240ADWR, it offers identical logic performance in a smaller, lower-profile package optimized for space-constrained designs.

Availability

SN74AS240ANSR is available at Aetrix Electronics and suitable for memory address buffering, system bus isolation, and clock distribution applications requiring stable component supply, long-term industrial lifecycle support, and RoHS-compliant packaging.

Supply support for SN74AS240ANSR 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 for industrial, automotive, and communications markets.

The SN74AS240ANSR belongs to TI's 74AS advanced Schottky TTL logic family, engineered for high-speed, high-drive digital interfacing in legacy and mixed-signal systems where robustness and timing predictability are critical.

FAQ

What is the maximum operating temperature range for SN74AS240ANSR?

The SN74AS240ANSR is rated for 0°C to +70°C ambient operation per its recommended conditions. Its SOP-NS package has a thermal impedance of 60°C/W, enabling reliable performance at full load within this range when PCB thermal design meets TI's layout guidelines for copper pour and via placement under the exposed pad.

Does SN74AS240ANSR support mixed-voltage interfacing with 3.3 V logic?

SN74AS240ANSR is a 5 V-only device with TTL-compatible input thresholds (VIH = 2 V, VIL = 0.8 V); it accepts 3.3 V logic-high signals safely but cannot drive 3.3 V inputs directly without level translation, as its VOH minimum is 2.4 V at IOL = –15 mA and VOL maximum is 0.55 V at IOL = 64 mA.

How does the pnp input structure in SN74AS240ANSR reduce DC loading?

The pnp input stage in SN74AS240ANSR limits input current to ≤1 mA across the full VI range, significantly lowering DC loading compared to standard TTL inputs. This reduces power draw on upstream drivers and minimizes voltage droop on shared logic rails, especially critical in high-fanout address bus configurations.

Can SN74AS240ANSR be used as a line driver for RS-232 or CAN physical layers?

No - SN74AS240ANSR is not rated for RS-232 or CAN physical layer signaling. It lacks the ±15 V voltage tolerance, slew rate control, and fault protection required for those standards. It is strictly intended for 5 V TTL-level intra-board digital interfacing, such as bus buffering and address latching.

Is SN74AS240ANSR pin-compatible with SN74LS240 or SN74ALS240A?

Yes - SN74AS240ANSR shares identical SOP-20 pinout, function mapping, and logic behavior with SN74ALS240A and SN74LS240 in the same package variant. All three feature dual 4-bit noninverting buffers with independent 1OE/2OE controls and Y1–Y4/Y1'–Y4' output grouping, enabling drop-in replacement where speed and drive strength upgrades are acceptable.