Texas Instruments SN74ALS253N

Overview

SN74ALS253N from Texas Instruments is a dual 4-line to 1-line data selector/multiplexer with independent 3-state outputs, designed for bus-organized digital systems. It features two independent 4-input sections (1C0–1C3 and 2C0–2C3), common select lines (A/B), individual output-enable inputs (1OE/2OE), and operates at 4.5–5.5 V over 0°C to 70°C.

For engineers reviewing the SN74ALS253N datasheet, SN74ALS253N pinout, SN74ALS253N application, or SN74ALS253N equivalent, key selection criteria include propagation delay (≤21 ns), 3-state output drive capability (24 mA sink), input compatibility with TTL/ALS logic families, and PDIP-16 packaging for through-hole prototyping and legacy industrial control boards.

Technical Context

The SN74ALS253N implements full binary decoding via internal inverters and AND-OR gates, enabling parallel-to-serial conversion by selecting one of four data inputs per section based on A/B address bits. Each section drives its own 3-state output (1Y/2Y) with dedicated enable control (1OE/2OE), allowing independent bus arbitration without external gating.

Its ALS (Advanced Low-Power Schottky) process delivers higher speed than standard LS while maintaining TTL-compatible voltage thresholds (VIH = 2.0 V min, VIL = 0.8 V max) and low quiescent current (ICC ≤ 14 mA when outputs disabled). The device supports hot insertion in bus systems due to controlled output disable timing (tPZL ≤ 16 ns, tPHZ ≤ 10 ns).

Key Specifications

Pinout & Package

SN74ALS253N uses a 16-pin plastic dual in-line package (PDIP-N), 300-mil width, with 0.1-inch lead pitch and through-hole mounting. Pin 1 is marked by a notch or dot; package height is 4.57 mm (0.180 inch).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual 4:1 multiplexer applications.

Compared with SN74AS253AD and SN74HC153N, the SN74ALS253N occupies a balanced niche: it delivers verified 21 ns performance and 24 mA drive within standard TTL voltage margins and power envelopes, making it optimal for cost-sensitive, noise-tolerant industrial designs where AS speed is unnecessary and HC drive is insufficient.

Availability

SN74ALS253N is available at Aetrix Electronics and suitable for industrial control I/O expansion, legacy test equipment signal routing, and microcontroller peripheral multiplexing requiring stable component supply across extended production lifecycles.

Supply support for SN74ALS253N 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 founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74ALS253N belongs to TI's legacy 74ALS logic family, engineered for high-reliability commercial applications where proven performance, long-term availability, and backward compatibility with TTL infrastructure are critical.

FAQ

What is the maximum clock frequency supported by SN74ALS253N in a multiplexing application?

The SN74ALS253N does not operate on a clock signal - it is a combinational logic device whose output responds asynchronously to input and select changes. Its 21 ns maximum propagation delay (data to Y) supports reliable operation in systems with signal transitions up to approximately 25 MHz, assuming proper setup/hold timing is maintained by the controlling logic. For precise timing analysis, refer to the SN74ALS253N switching characteristics table specifying tPLH/tPHL under CL = 50 pF conditions.

Can SN74ALS253N interface directly with 3.3 V microcontrollers?

No - the SN74ALS253N is a 5 V-only device with TTL-compatible input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and requires VCC = 4.5–5.5 V. Driving its inputs from a 3.3 V microcontroller may result in marginal or non-functional high-level recognition due to insufficient VIH margin. A level-shifting buffer or resistor-divider network is required for safe 3.3 V → 5 V interface; direct connection risks unreliable operation or increased power consumption.

Does SN74ALS253N support hot-swapping on a live bus?

The SN74ALS253N supports controlled bus insertion via its 3-state outputs and defined disable timing (tPZL ≤ 16 ns, tPHZ ≤ 10 ns), but it lacks explicit hot-swap protection features such as slew-rate limiting or undervoltage lockout. Safe hot insertion requires external current-limiting resistors, careful sequencing of VCC relative to bus signals, and adherence to system-level hot-swap protocols. TI does not characterize or guarantee SN74ALS253N for unassisted hot-swap operation.

What is the purpose of the NC pins on SN74ALS253N?

The SN74ALS253N has no NC (No Connect) pins in its PDIP-16 package - all 16 pins are assigned functional roles as defined in the pinout table (pins 1–16 correspond to 1OE, 1C0, ..., VCC). NC designations appear only in ceramic packages (e.g., FK, J) where mechanical pin positions lack internal bonding; the PDIP variant fully utilizes all leads for signal, power, and ground connections.

How does SN74ALS253N differ from SN74LS253 in practical design use?

The SN74ALS253N offers significantly faster propagation delay (21 ns vs. 30–35 ns for LS), lower power consumption (ICC ≤ 14 mA vs. ~20 mA for LS), and improved noise immunity due to tighter VIH/VIL specifications. These differences allow denser timing margins in high-speed bus systems and reduced thermal load in compact enclosures. However, both share identical pinout, function table, and DC characteristics - making SN74ALS253N a drop-in speed upgrade for existing LS253 designs where timing or power is constrained.