Texas Instruments CD74HC138EG4

Overview

CD74HC138EG4 from Texas Instruments is a high-speed CMOS 3-to-8 line decoder/demultiplexer with active-low outputs, operating across 2 V to 6 V supply range, featuring 13 ns typical propagation delay at 5 V/15 pF, -55°C to +125°C temperature rating, and three enable inputs (G0, G1, G2) for cascading in memory address decoding applications.

For engineers reviewing the CD74HC138EG4 datasheet, CD74HC138EG4 pinout, CD74HC138EG4 application, or CD74HC138EG4 equivalent, this device serves as a logic-level address selector in industrial control I/O expansion, microcontroller peripheral decoding, and bus multiplexing where low-power, wide-temperature, and TTL-compatible drive capability are required.

Technical Context

The CD74HC138EG4 implements a standard 3-input binary address decoder with three independent enable inputs - one active-high (G2) and two active-low (G0, G1) - enabling hierarchical decoding without external gating. Its output behavior is strictly inverting: only the selected Y0–Y7 output goes low while all others remain high when enabled.

It uses silicon-gate CMOS technology with balanced rise/fall times, fanout of 10 LSTTL loads on standard outputs, and input thresholds defined at 30% VCC (VIH/VIL), ensuring robust noise immunity across its full 2–6 V operating range.

Key Specifications

Pinout & Package

CD74HC138EG4 is supplied in a 16-pin plastic dual in-line package (PDIP-N), body size 25.40 mm × 6.35 mm, with through-hole mounting and industry-standard lead pitch (2.54 mm).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC138N and CD74HCT138E, CD74HC138EG4 delivers broader voltage flexibility (2–6 V), extended temperature support (-55°C to +125°C), and higher noise immunity - making it optimal for ruggedized embedded systems where supply variation and environmental stress are design constraints.

Availability

CD74HC138EG4 is available at Aetrix Electronics and suitable for industrial control systems, aerospace avionics interfaces, and high-reliability power conversion monitoring requiring stable component supply across extreme temperature cycles and long product lifecycles.

Supply support for CD74HC138EG4 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 designing analog ICs, embedded processors, and logic devices for industrial, automotive, and communications markets.

The CD74HC138EG4 belongs to TI's HC-series high-speed CMOS logic family, engineered for low-power, wide-temperature, and mixed-voltage compatibility in mission-critical decoding and routing tasks.

FAQ

What is the maximum supply voltage rating for CD74HC138EG4?

The absolute maximum supply voltage for CD74HC138EG4 is 7 V, but the recommended operating range is 2 V to 6 V. Operating above 6 V risks exceeding safe junction temperature and may cause accelerated parametric drift or latch-up. All DC and AC specifications in the datasheet are guaranteed only within the 2–6 V range, and TI does not characterize performance beyond that limit. For sustained reliability, maintain VCC ≤ 6 V.

Does CD74HC138EG4 support cascading with other decoders?

Yes, CD74HC138EG4 supports cascading via its three enable inputs: G0 and G1 are active-low, G2 is active-high. To cascade two devices, connect the outputs of a master CD74HC138EG4 to G0/G1/G2 of slave units, allowing hierarchical decoding of up to 64 outputs (8 × 8). The function table confirms that any active strobe forces all outputs high, enabling clean, glitch-free multi-level selection without external logic.

What is the output state of CD74HC138EG4 when all enable inputs are inactive?

When any of the enable inputs (G0, G1, or G2) is in the inactive state - i.e., G0 = high, G1 = high, or G2 = low - all eight outputs (Y0–Y7) are forced high regardless of A0–A2 values. This is explicitly defined in the function table and functional description: the device enters a high-impedance-equivalent disabled mode with all outputs at VOH, preventing bus contention during deselection.

Can CD74HC138EG4 drive standard TTL loads directly?

Yes, CD74HC138EG4 can drive up to 10 LSTTL loads per output, as specified in its fanout rating. At VCC = 4.5 V, it guarantees VOL ≤ 0.33 V at IOL = 4 mA and VOH ≥ 3.84 V at IOH = –4 mA - meeting LS-TTL VOH/VOL thresholds. This allows direct interface with 74LSxx series without level-shifting or buffering, provided total capacitive load remains ≤50 pF for timing compliance.

Is CD74HC138EG4 RoHS compliant and lead-free?

Yes, CD74HC138EG4 is RoHS compliant and features a lead-free finish (NIPDAU). Per TI's packaging addendum, the PDIP-N package carries "Yes" in the RoHS column and specifies NIPDAU (nickel-palladium-gold) as the lead finish. It meets JEDEC J-STD-020 moisture sensitivity Level-1 requirements and is rated for peak reflow temperatures up to 260°C, confirming full compliance with current environmental directives.