Texas Instruments SN74HC138QDRG4Q1

Overview

SN74HC138QDRG4Q1 from Texas Instruments is an automotive-qualified 3-line-to-8-line decoder/demultiplexer in SOIC-16 package, operating from 2 V to 6 V, with typical propagation delay of 15 ns at 5 V, ±4-mA output drive, and low 80-µA max ICC - used for memory decoding and data routing in engine control units and ADAS domain controllers.

For engineers reviewing the SN74HC138QDRG4Q1 datasheet, SN74HC138QDRG4Q1 pinout, SN74HC138QDRG4Q1 application, or SN74HC138QDRG4Q1 equivalent, key selection criteria include automotive temperature range (−40°C to 125°C), three enable inputs (G1, G2A, G2B) for cascading, active-low outputs, and compatibility with LSTTL loads in safety-critical logic subsystems.

Technical Context

This device implements combinational logic decoding using standard HC CMOS technology, with three binary select inputs (A, B, C) and three enable terminals (G1 high-active, G2A/G2B low-active) that jointly determine which of eight Y0–Y7 outputs is asserted low. All outputs are active-low and open-drain compatible only when used with external pull-ups.

Propagation delay is tightly specified across VCC (2 V to 6 V) and temperature (−40°C to 125°C), with tpd ≤ 46 ns at 6 V and ≤ 54 ns at 4.5 V (CL = 50 pF). Input transition times are constrained to ≤ 400 ns at 6 V to ensure valid timing margins in synchronous memory decode trees.

Key Specifications

Pinout & Package

SN74HC138QDRG4Q1 is housed in a 16-pin SOIC (D) package with 1.27-mm pitch, 10.3-mm body width, and RoHS-compliant NiPdAu lead finish. Pin 1 is located in quadrant Q1 per tape-and-reel orientation standard.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC138QDRG4Q1, SN74HCT138QDRQ1 offers improved input threshold compatibility with legacy 5 V TTL, while MC74HC138ADR2G extends low-temperature capability beyond automotive spec - neither is pin-compatible without layout review due to minor package dimensional variances.

Availability

SN74HC138QDRG4Q1 is available at Aetrix Electronics and suitable for engine control units, ADAS domain controllers, and body control modules requiring stable component supply across automotive production lifecycles.

Supply support for SN74HC138QDRG4Q1 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 company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for automotive, industrial, and personal electronics markets.

The SN74HC138-Q1 belongs to TI's automotive logic portfolio, engineered specifically for high-reliability decoding in memory and data-routing subsystems where AEC-Q100 qualification and sub-20-ns timing are mandatory.

FAQ

What is the maximum clock frequency supported by SN74HC138QDRG4Q1?

SN74HC138QDRG4Q1 is a combinational logic device without a clock input; it does not operate at a clock frequency. Its speed is defined by propagation delay - up to 46 ns at 6 V - making it suitable for address decoding in systems with memory access cycles ≥ 50 ns. The SN74HC138QDRG4Q1 responds asynchronously to input changes, with no setup/hold timing constraints beyond specified input transition rates.

Does SN74HC138QDRG4Q1 support 3.3 V operation?

Yes, SN74HC138QDRG4Q1 supports 3.3 V operation within its 2 V to 6 V VCC range. At 3.3 V, it delivers guaranteed VOH ≥ 3.15 V and VOL ≤ 0.26 V under 4-mA load, ensuring interoperability with 3.3 V microcontrollers and FPGAs. Input thresholds scale with VCC, maintaining noise margin across the full voltage range.

Can SN74HC138QDRG4Q1 be used as a demultiplexer?

Yes, SN74HC138QDRG4Q1 functions as a 1-to-8 demultiplexer when one enable input (e.g., G1) is used as the data input and A/B/C serve as select lines. With G2A and G2B held low, asserting G1 high routes the logic state to the selected Yx output (active-low), enabling serial-to-parallel data distribution in automotive diagnostics interfaces.

What is the thermal resistance θJA for SN74HC138QDRG4Q1?

The SOIC-16 package of SN74HC138QDRG4Q1 has a thermal resistance θJA of 73°C/W under JEDEC-standard conditions. This value assumes a two-layer PCB with 1-in² copper pour under the package; actual junction temperature rise depends on layout, airflow, and ambient conditions. For continuous operation at 125°C ambient, power dissipation should remain below 170 mW to maintain safe junction temperatures.

Is SN74HC138QDRG4Q1 pin-compatible with non-automotive variants like SN74HC138N?

No, SN74HC138QDRG4Q1 is not pin-compatible with through-hole SN74HC138N (DIP-16), though it shares identical logic functionality and pin assignments with other SOIC-16 variants like SN74HC138DR. The "Q1" suffix denotes AEC-Q100 qualification and automotive temp range, but mechanical dimensions and solder pad layout match standard SOIC-16 footprints - verified against TI's D-package drawing.