Texas Instruments SN74LVC138ANS

Overview

SN74LVC138ANS from Texas Instruments is a 3-to-8 line inverting decoder/demultiplexer with three binary address inputs (A0–A2), three enable inputs (E1, E2 active LOW; E3 active HIGH), and eight mutually exclusive active-LOW outputs (Y0–Y7). It operates from 1.65 V to 3.6 V supply, supports 5 V tolerant inputs, and delivers <7.5 ns propagation delay at 3.3 V for memory chip select and address decoding in industrial microcontroller systems.

For engineers reviewing the SN74LVC138ANS datasheet, SN74LVC138ANS pinout, SN74LVC138ANS application, or SN74LVC138ANS equivalent, key selection criteria include its wide VCC range (1.65–3.6 V), 5 V input tolerance, -40 °C to +125 °C operating temperature, inverting output logic, and parallel expandability to 1-of-32 decoding using four devices and one inverter.

Technical Context

The SN74LVC138ANS implements combinational logic decoding with strict mutual exclusivity: only one output goes LOW when all enables are asserted (E1=L, E2=L, E3=H) and a unique 3-bit address is applied. Its enable architecture-two active-LOW and one active-HIGH-enables hierarchical expansion without external logic inversion for cascaded decoding.

Designed for low-voltage CMOS systems, it interfaces directly with TTL-level signals and drives 50 Ω transmission lines at 125 °C. Static characteristics include VIH thresholds scaling with VCC (e.g., 2.0 V min at VCC = 2.7–3.6 V) and VOL ≤ 0.6 V at 12 mA sink current, ensuring robust noise margins in mixed-signal embedded control buses.

Key Specifications

Pinout & Package

SN74LVC138ANS uses the SO16 (SOT109-1) package: plastic small outline, 16-pin, 3.9 mm body width, 1.27 mm lead pitch. Pin 1 is index-marked; thermal pad is non-electrical and may be left floating or tied to GND.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC138ANS, 74LVC138AD offers identical electrical behavior and drop-in replacement capability in SO16 layout, while SN74HC138N trades speed and voltage flexibility for broader supply range but lacks 5 V tolerance and low-voltage support - making SN74LVC138ANS optimal for modern mixed-voltage embedded systems.

Availability

SN74LVC138ANS is available at Aetrix Electronics and suitable for memory address decoding, microcontroller peripheral selection, and industrial I/O expansion requiring stable component supply across automotive, industrial automation, and medical device production programs.

Supply support for SN74LVC138ANS 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 delivering analog and embedded processing solutions for industrial, automotive, and personal electronics markets.

The SN74LVC138ANS belongs to TI's LVC logic family, engineered for low-voltage, high-speed, 5 V tolerant operation in space-constrained embedded control applications.

FAQ

What is the maximum supply voltage for SN74LVC138ANS?

The absolute maximum supply voltage for SN74LVC138ANS is +6.5 V, but the recommended operating range is 1.65 V to 3.6 V. Operation above 3.6 V risks violating the device's specified static and dynamic characteristics, including increased ICC and potential output stage stress. Always maintain VCC within the recommended range for guaranteed timing, drive strength, and logic threshold compliance in SN74LVC138ANS applications.

Does SN74LVC138ANS support 1.8 V operation?

Yes, SN74LVC138ANS fully supports 1.8 V operation: its recommended VCC range starts at 1.65 V, and all specifications-including VIH (min 1.08 V), VOL (≤0.45 V at 4 mA), and tpd (≤11.5 ns)-are guaranteed down to this level. This makes SN74LVC138ANS suitable for direct integration into 1.8 V microcontroller subsystems without level translation, unlike HC-series alternatives.

How many enable inputs does SN74LVC138ANS have, and what are their polarities?

SN74LVC138ANS has three enable inputs: E1 and E2 are active LOW, and E3 is active HIGH. All three must be simultaneously asserted (E1=L, E2=L, E3=H) for decoding to occur; any deviation forces all outputs HIGH. This triple-enable structure enables flexible hierarchical expansion-for example, using E1/E2 from a higher-level decoder and E3 as a local strobe in SN74LVC138ANS-based systems.

Can SN74LVC138ANS be used as a demultiplexer?

Yes, SN74LVC138ANS can function as an 1-to-8 demultiplexer: configure one active-LOW enable (e.g., E1) as the data input, use A0–A2 as address lines, and tie E2 and E3 to fixed valid states (E2=L, E3=H). The selected output mirrors the inverted data state, providing eight independent data paths. Unused enables must be hard-wired-not left floating-to prevent metastability in SN74LVC138ANS demux mode.

What is the output logic polarity of SN74LVC138ANS?

SN74LVC138ANS provides active-LOW (inverting) outputs: when enabled and addressed, exactly one output (Y0–Y7) drives LOW while all others remain HIGH. This matches standard chip select (CS#) and output enable (OE#) conventions in memory and peripheral ICs. The inverting nature is intrinsic to the device's logic design and cannot be disabled; non-inverting behavior requires external inverters or alternative part selection.