Texas Instruments SN74HC138QPWRQ1

Overview

SN74HC138QPWRQ1 from Texas Instruments is an automotive-qualified 3-line-to-8-line decoder/demultiplexer in a 16-pin TSSOP package, operating from 2 V to 6 V, with typical propagation delay of 15 ns at 5 V, ±4-mA output drive, and low ICC of 80 µA max - used for memory decoding and data routing in engine control units and ADAS sensor interfaces.

For engineers reviewing the SN74HC138QPWRQ1 datasheet, SN74HC138QPWRQ1 pinout, SN74HC138QPWRQ1 application, or SN74HC138QPWRQ1 equivalent, key selection criteria include automotive temperature range (−40°C to 125°C), enable-input logic architecture (two active-low, one active-high), output drive capability, propagation delay vs. memory access timing, and TSSOP thermal performance (θJA = 108°C/W).

Technical Context

The SN74HC138QPWRQ1 implements positive-logic binary decoding with three select inputs (A, B, C) and three enable terminals (G1, G2A, G2B), where G1 is active-high and G2A/G2B are active-low - enabling cascading without external inverters. Its output structure provides eight active-low decoded outputs (Y0–Y7), each capable of sinking or sourcing up to ±4 mA at 5 V.

Designed for high-speed memory systems, it achieves tpd ≤ 31 ns (max) at 6 V with CL = 50 pF, and supports demultiplexing via G1 or G2A as data input. Input thresholds scale with VCC (VIH = 3.15 V min at 4.5 V; VIL = 1.35 V max), ensuring robust noise immunity across supply voltages.

Key Specifications

Pinout & Package

TSSOP-16 (PW) package, 4.4 mm × 5.0 mm body, 1.2 mm max height, 0.65 mm pitch, moisture sensitivity level 3 (260°C peak reflow, 168 hr floor life).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC138QPWRQ1, SN74HC238QPWRQ1 offers inverted output polarity without timing or power trade-offs, while MC74HC138ADR2G provides identical functionality at lower qualification cost - making the former ideal for polarity-aligned systems and the latter suitable for non-automotive-qualified subsystems.

Availability

SN74HC138QPWRQ1 is available at Aetrix Electronics and suitable for engine control units, ADAS sensor hubs, body control modules, and electric power steering systems requiring stable component supply across automotive production lifecycles.

Supply support for SN74HC138QPWRQ1 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, embedded processing, and connectivity solutions for automotive, industrial, and consumer applications.

The SN74HC138QPWRQ1 belongs to TI's automotive HC logic family, engineered specifically for high-speed, low-power memory decoding and data routing in safety-critical vehicle subsystems.

FAQ

What is the maximum clock frequency supported by SN74HC138QPWRQ1?

The SN74HC138QPWRQ1 is not a clocked device and has no defined clock frequency. It is a combinational logic decoder with propagation delay (tpd) of 15 ns typical at 5 V. Its effective maximum switching rate depends on input transition times and load capacitance - for CL = 50 pF, maximum toggle rate is ~15 MHz under nominal conditions. Always verify timing margins against your specific address bus slew rate and fanout.

Does SN74HC138QPWRQ1 support mixed-voltage operation between inputs and outputs?

No, SN74HC138QPWRQ1 does not support mixed-voltage operation. All inputs and outputs are referenced to the same VCC supply (2 V to 6 V). Input thresholds (VIH/VIL) scale with VCC, and output VOH/VOL are bounded by VCC and GND. Interfacing with 3.3 V controllers and 5 V peripherals requires external level-shifting circuitry if VCC is fixed to one rail.

Can SN74HC138QPWRQ1 be used as a 1-to-8 demultiplexer, and how is that configured?

Yes, SN74HC138QPWRQ1 can operate as a 1-to-8 demultiplexer. Configure one enable input (e.g., G1) as the data input, hold the other two enables (G2A, G2B) LOW, and use A, B, C as the 3-bit select lines. When G1 = HIGH, the selected Yx output goes LOW; when G1 = LOW, all outputs remain HIGH. This provides true demux behavior with active-low outputs and no additional components.

What is the recommended PCB layout practice for SN74HC138QPWRQ1 in automotive applications?

For SN74HC138QPWRQ1 in automotive designs, place a 100 nF X7R ceramic capacitor within 3 mm of VCC and GND pins, use solid ground plane beneath the TSSOP footprint, route address and enable traces as matched-length pairs if timing-critical, and avoid routing high-speed signals adjacent to decoder pins. Follow TI's PW0016A land pattern - 0.45 mm pad width, 0.65 mm pitch, 1.5 mm length - to ensure reliable reflow and mechanical stability under thermal cycling.

Is SN74HC138QPWRQ1 pin-compatible with the commercial SN74HC138?

Yes, SN74HC138QPWRQ1 is pin-compatible with the commercial SN74HC138 in TSSOP-16 (PW) package, sharing identical pinout, electrical behavior, and logic function. However, SN74HC138QPWRQ1 adds AEC-Q100 qualification, extended temperature range (−40°C to 125°C), and enhanced ESD robustness (2000 V HBM), making it suitable for automotive deployment where the commercial version is not certified.