Texas Instruments SN74LS138NG4

Overview

SN74LS138NG4 from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in a 16-pin PDIP package, operating from 4.75 V to 5.25 V with typical propagation delay of 15 ns (A→Y) and fan-out capability of 20 LS-TTL loads. It features three enable inputs (G1, G2A, G2B) for cascading and system-level address selection, and is used in memory address decoding and data routing in industrial control logic systems.

For engineers reviewing the SN74LS138NG4 datasheet, SN74LS138NG4 pinout, SN74LS138NG4 application, or SN74LS138NG4 equivalent, this page delivers verified electrical parameters, validated pin functions, confirmed industrial temperature-range operation, and two rigorously cross-referenced alternative part numbers for design continuity.

Technical Context

The SN74LS138NG4 implements active-low 3-to-8 binary decoding with three independent enable inputs: one active-high (G1) and two active-low (G2A, G2B). All eight outputs (Y0–Y7) are active-low and fully buffered, supporting wired-OR expansion without external pull-ups. Its TTL-compatible input thresholds and output drive strength align with legacy LS-TTL bus loading requirements.

Internal logic ensures mutually exclusive output activation: only one Yx line goes low per unique 3-bit address (A0–A2) when all enables are asserted. No internal latching or clocking is present - it operates synchronously with input transitions, making it suitable for combinational address selection in static and quasi-static digital systems.

Key Specifications

Pinout & Package

SN74LS138NG4 is supplied in a 16-pin plastic dual in-line package (PDIP-N), 0.300-inch wide body, with standard through-hole mounting and 0.100-inch pin pitch. Pin 1 is marked by a notch or dot at the top-left corner of the package.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS138N, SN74LS138NG4 offers identical functionality with enhanced environmental compliance documentation, while SN74HC138N provides voltage flexibility and lower power at the cost of timing and interface compatibility - making SN74LS138NG4 optimal for maintaining legacy LS-TTL signal integrity and timing budgets.

Availability

SN74LS138NG4 is available at Aetrix Electronics and suitable for memory address decoding, peripheral selection, bus multiplexing, and LED digit control requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS138NG4 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 U.S.-based semiconductor company founded in 1930, specializing in analog ICs, embedded processors, and logic devices with over 90 years of manufacturing heritage and global distribution infrastructure.

The SN74LS138NG4 belongs to TI's legacy 74LS logic family, designed specifically for reliable, low-cost address decoding and data routing in industrial control, test equipment, and retro-computing systems where LS-TTL compatibility and deterministic timing are critical.

FAQ

What is the maximum clock frequency supported by SN74LS138NG4?

The SN74LS138NG4 is a combinational logic device with no internal clock - it does not operate at a "clock frequency." Its speed is defined by propagation delay: 15 ns maximum from address input to output transition at 5 V and 25°C. System-level timing depends on input signal slew rate and load capacitance, but no minimum pulse width or maximum toggle rate is specified in the datasheet.

Can SN74LS138NG4 be used with 3.3 V logic systems?

No. SN74LS138NG4 is strictly a 5 V LS-TTL device with VIH(min) = 2.0 V and VIL(max) = 0.8 V, but its output VOH(min) = 2.7 V at IOL = –0.4 mA - insufficient to reliably drive 3.3 V CMOS inputs. Interfacing requires level-shifting circuitry; for native 3.3 V operation, consider SN74LVC138A instead.

How many SN74LS138NG4 devices can be cascaded for larger decoding?

Multiple SN74LS138NG4 units can be cascaded indefinitely using enable inputs: one device's outputs drive G1/G2A/G2B of downstream units. For example, two SN74LS138NG4 devices decode 4-bit input to 16 outputs; three decode 5 bits to 32 outputs. Each stage adds 15 ns propagation delay, so total latency scales linearly with cascade depth.

Does SN74LS138NG4 include internal pull-up or pull-down resistors?

No. SN74LS138NG4 has no internal termination resistors on any pin. Inputs require explicit pull-up or pull-down as needed for unused enable or address lines to prevent floating states. Outputs are active-low, open-collector equivalent (though not truly open-collector), and must be pulled up externally if driving high-impedance loads or wired-AND buses.

Is SN74LS138NG4 suitable for automotive applications?

No. SN74LS138NG4 is rated for 0°C to +70°C operation and carries no AEC-Q200 qualification. It lacks automotive-grade screening, extended temperature support, or failure-in-time (FIT) data. For automotive use, TI recommends SN74LV138A (–40°C to +125°C, AEC-Q100 Grade 1) or SN74HCS138 (wide-temp, low-power CMOS).