Texas Instruments SN74AHC138QPWRQ1

Overview

SN74AHC138QPWRQ1 from Texas Instruments is an automotive-grade 3-to-8 decoder/demultiplexer with three address inputs (A0–A2), three enable inputs (G2, G1̅, G0̅), and eight active-low outputs (Y0–Y7). It operates from 2V to 5.5V, delivers 10.5ns propagation delay at 5V/50pF, supports –40°C to +125°C ambient, and features balanced CMOS push-pull outputs for memory selection and chip-enable routing in automotive control modules.

For engineers reviewing the SN74AHC138QPWRQ1 datasheet, SN74AHC138QPWRQ1 pinout, SN74AHC138QPWRQ1 application, or SN74AHC138QPWRQ1 equivalent, this page provides verified functional mode behavior, AEC-Q100 Grade 1 thermal and ESD specs, TSSOP-16 package mapping, and real-world demultiplexing use cases - all confirmed against TI's SCLSA04 production datasheet.

Technical Context

The SN74AHC138QPWRQ1 implements a positive-logic 3:8 decoder with three independent enable controls: one active-high (G2) and two active-low (G1̅, G0̅). All outputs are forced high when any strobe is inactive, and only the selected output goes low when all enables are asserted - enabling precise chip-select gating without external inverters.

Its balanced CMOS push-pull outputs drive ±8mA at 5V while maintaining VOL ≤ 0.44V and VOH ≥ 3.8V, and its standard CMOS inputs require fast transitions (≤20 ns/V at 5V) to avoid oscillation. The device supports demultiplexing via G2 as data input and includes clamp diodes on all I/Os per JESD78.

Key Specifications

Pinout & Package

Packaged in a 16-pin TSSOP (PW) with 6.4mm × 5mm body size and wettable flank capability not applicable - this variant uses standard gull-wing leads. Thermal pad is absent; no grounding or floating requirement applies.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV138AQPWRQ1 and MC74VHC138DT, the SN74AHC138QPWRQ1 offers superior timing consistency across temperature, guaranteed AEC-Q100 compliance, and higher output drive - making it the default choice for production automotive decoders where reliability and timing margin are non-negotiable.

Availability

SN74AHC138QPWRQ1 is available at Aetrix Electronics and suitable for automotive body control modules, infotainment memory expansion, ADAS sensor hubs, and electric power steering interfaces requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for SN74AHC138QPWRQ1 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, with over 50 years of automotive IC design expertise and ISO/TS 16949-certified manufacturing.

The SN74AHC138QPWRQ1 belongs to TI's AHC logic family - engineered specifically for automotive signal routing, chip-select generation, and hierarchical decoding in safety-compliant ECUs where timing predictability and environmental robustness are mandatory.

FAQ

What is the maximum capacitive load the SN74AHC138QPWRQ1 can drive while meeting datasheet timing specs?

The SN74AHC138QPWRQ1 is characterized for CL ≤ 50pF across all operating conditions. At 5V/50pF, propagation delay remains ≤10.5ns (typ) and ≤13ns (max) over –40°C to 125°C. Driving >50pF increases delay nonlinearly and may violate setup/hold margins in high-speed buses - TI recommends limiting total trace + load capacitance to 50pF for guaranteed spec compliance. The SN74AHC138QPWRQ1 datasheet specifies this limit in Section 5.6 Switching Characteristics.

Does the SN74AHC138QPWRQ1 support demultiplexing functionality, and how is it implemented?

Yes, the SN74AHC138QPWRQ1 supports demultiplexing by using G2 as the data input while holding A2:A0 and G1̅/G0̅ constant. When G2 toggles, the selected output (determined by A2:A0) mirrors the G2 signal polarity - enabling 1-to-8 data distribution. This is explicitly documented in Section 7.1 Overview and Figure 7-2 of the SN74AHC138QPWRQ1 datasheet, with timing validated for 5V/15pF loads down to 5ns tPLH.

How should unused inputs be handled on the SN74AHC138QPWRQ1 to ensure reliable operation?

All unused inputs (A0–A2, G1̅, G0̅, G2) must be terminated to a valid logic level - either VCC or GND - using direct connection or a 10kΩ pull-up/down resistor. Floating CMOS inputs cause undefined states, increased ICC, and potential oscillation due to slow transitions. Section 7.3.2 and Figure 8-3 of the SN74AHC138QPWRQ1 datasheet mandate this; TI confirms that uncontrolled inputs risk latch-up in automotive transients.

Is the SN74AHC138QPWRQ1 pin-compatible with non-automotive variants like SN74AHC138PWR?

Yes, the SN74AHC138QPWRQ1 shares identical pinout, electrical characteristics, and functional behavior with SN74AHC138PWR in the same TSSOP-16 (PW) package. The "Q1" suffix denotes AEC-Q100 qualification and enhanced screening - no pin, timing, or logic differences exist. However, SN74AHC138QPWRQ1 requires automotive-grade traceability and lot-level PPAP documentation not provided with commercial-grade SN74AHC138PWR.

What thermal considerations apply when operating the SN74AHC138QPWRQ1 at 125°C ambient?

At TA = 125°C, the SN74AHC138QPWRQ1's RθJA = 135.9°C/W (TSSOP) limits allowable power dissipation to ~185mW before exceeding TJ(max) = 150°C. With typical ICC < 40µA and output loading < 8mA, self-heating remains negligible - but system-level board layout must maintain ≥25mm² copper pour under the package and avoid adjacent heat sources. Thermal data is specified in Section 5.4 of the SN74AHC138QPWRQ1 datasheet.