Texas Instruments SN74F138NS

Overview

SN74F138NS from Texas Instruments is a 3-line to 8-line decoder/demultiplexer IC designed for high-speed memory decoding and data routing. It features three enable inputs (G1, G2A, G2B), active-low outputs, propagation delays as low as 2.7 ns (tPLH), operates at 4.5–5.5 V, and is rated for 0°C to 70°C industrial temperature range.

For engineers reviewing the SN74F138NS datasheet, SN74F138NS pinout, SN74F138NS application, or SN74F138NS equivalent, key selection considerations include its TTL-compatible input thresholds (VIL = 0.8 V, VIH = 2 V), 20 mA output sink capability, cascading support via dual active-low enables, and SOP-16 package compatibility with automated SMT assembly.

Technical Context

The SN74F138NS implements positive-logic binary decoding with three select inputs (A, B, C) and three independent enables (G1 high-active, G2A/G2B low-active), allowing flexible hierarchical expansion without external inverters. Its internal NAND-based architecture ensures deterministic output states per the function table.

It supports demultiplexing by using an enable input (e.g., G1) as a data line while A/B/C control channel selection - enabling 1-to-8 signal distribution. All outputs are active-low open-collector equivalents, compatible with standard TTL fanout and wired-OR bus configurations.

Key Specifications

Pinout & Package

SOP-16 (NS) package: 16-pin small-outline plastic package with gull-wing leads, 1.27 mm pitch, 10.4 mm × 5.3 mm body size, maximum height 2.00 mm, RoHS-compliant NIPDAU finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 3-to-8 decoder applications.

Compared with SN74LS138N and SN74HC138DR, the SN74F138NS delivers optimal balance of speed, TTL compatibility, and industrial temperature range - making it the preferred choice for legacy 5 V embedded systems requiring sub-10 ns decode latency.

Availability

SN74F138NS is available at Aetrix Electronics and suitable for memory decoding, peripheral selection, LED driver control, and automated test equipment requiring stable component supply and long-term industrial-grade availability.

Supply support for SN74F138NS 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 with broad industrial and automotive qualification.

The SN74F138NS belongs to TI's 74F family of fast TTL logic devices, engineered specifically for high-speed memory decoding and data-routing applications where propagation delay and fanout are critical design parameters.

FAQ

What is the maximum clock or signal frequency supported by the SN74F138NS?

The SN74F138NS is not a clocked device and has no specified maximum operating frequency. Its performance is defined by propagation delay (2.7–9 ns), making it suitable for address decode and static selection tasks in systems with memory access times ≥15 ns. For dynamic routing, ensure setup/hold timing relative to enable and select edges is met per the function table.

Does the SN74F138NS require external pull-up resistors on its outputs?

Yes, the SN74F138NS outputs are active-low and internally open-collector equivalents. External pull-up resistors (typically 1–10 kΩ to VCC) are required to establish a valid HIGH logic level on Y0–Y7. The value depends on capacitive load and desired rise time; 4.7 kΩ is commonly used for TTL-compatible bus driving.

Can the SN74F138NS be used as a 1-to-8 demultiplexer?

Yes, the SN74F138NS can operate as a demultiplexer by using G1 as the data input and A/B/C as the 3-bit channel address. When G2A and G2B are held low and G1 toggles, the selected Yx output mirrors G1's state (inverted due to active-low output). This configuration requires no additional logic and is explicitly supported in the datasheet.

Is the SN74F138NS pin-compatible with the SN74LS138N?

Yes, the SN74F138NS and SN74LS138N share identical pinouts, logic function, and DC electrical specifications (VIL/VIH, VOL/VOH). However, SN74F138NS offers significantly faster propagation (≤9 ns vs. ≤20 ns) and higher ICC (13–20 mA vs. ~2 mA), so thermal and power delivery must be re-evaluated in drop-in replacements.

What is the meaning of "NS" in SN74F138NS?

The "NS" suffix in SN74F138NS denotes the SOP (Small Outline Package) variant with 16 pins, standardized under TI's NS0016A package drawing. It indicates a surface-mount, gull-wing leaded plastic package with 1.27 mm pitch, distinct from PDIP (N), SOIC (D), or ceramic packages - critical for PCB land pattern and assembly process selection.