Texas Instruments SN74HCS238QBQBRQ1

Overview

SN74HCS238QBQBRQ1 from Texas Instruments is an automotive-qualified 3-to-8 line decoder/demultiplexer with Schmitt-trigger inputs, designed for memory address decoding and data routing in safety-critical vehicle systems. It operates from 2 V to 6 V, delivers ±7.8-mA output drive at 6 V, features typical ICC of 100 nA, and supports –40°C to +125°C ambient operation per AEC-Q100 Grade 1.

For engineers reviewing the SN74HCS238QBQBRQ1 datasheet, SN74HCS238QBQBRQ1 pinout, SN74HCS238QBQBRQ1 application, or SN74HCS238QBQBRQ1 equivalent, key selection criteria include its triple strobe-enabled output gating (G2, G1, G0), hysteresis-based noise immunity (ΔVT = 0.6 V min at 6 V), low-power CMOS push-pull outputs, and WQFN-16 package compatibility with automotive thermal and ESD requirements (HBM Level 2, CDM Level C6).

Technical Context

The SN74HCS238QBQBRQ1 implements a single 3:8 decoder with three address inputs (A2–A0) and three independent strobe inputs (G2, active-high; G1 and G0, active-low) that force all eight outputs (Y0–Y7) low when asserted. Its Schmitt-trigger inputs provide hysteresis (VT+ − VT− = 0.6 V min at 6 V), enabling robust operation with slow-rising or noisy control signals common in automotive harness environments.

Outputs are CMOS push-pull with balanced sourcing/sinking capability (±7.8 mA at 6 V), supporting direct interfacing with standard logic loads up to 50 pF. The device uses silicon-gate CMOS technology, ensuring rail-to-rail VOH/VOL performance (VOH ≥ VCC − 0.1 V, VOL ≤ 0.33 V at 6 V/7.8 mA) and ultra-low static current (ICC ≤ 2 µA max).

Key Specifications

Pinout & Package

SN74HCS238QBQBRQ1 is packaged in a 16-pin WQFN (BQB) with 3.50 mm × 2.50 mm body size and exposed thermal pad. The pad may be connected to GND or left floating; it must not be tied to any signal or supply voltage.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCS138QDRQ1 and MC74HC238ADTR2G, SN74HCS238QBQBRQ1 uniquely combines AEC-Q100 Grade 1 qualification, integrated Schmitt-trigger noise immunity, and compact WQFN-16 packaging - making it the only option qualified for direct use in ASIL-B–relevant subsystems requiring both robust signal integrity and space-constrained layouts.

Availability

SN74HCS238QBQBRQ1 is available at Aetrix Electronics and suitable for automotive body control modules, engine control units, ADAS domain controllers, and infotainment system peripheral selection requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN74HCS238QBQBRQ1 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 specializing in analog and embedded processing technologies, with leadership in automotive-grade IC design, manufacturing, and qualification.

The SN74HCS238QBQBRQ1 belongs to TI's HCS logic family - engineered specifically for automotive applications demanding low power, high noise immunity, and AEC-Q100 compliance in harsh electrical environments.

FAQ

What is the maximum capacitive load SN74HCS238QBQBRQ1 can drive while maintaining specified timing?

The SN74HCS238QBQBRQ1 is characterized for CL = 50 pF in its switching characteristics table. Driving loads exceeding 50 pF increases propagation delay and transition time - for example, tpd rises from 7 ns (typical at 6 V) to >16 ns at worst-case 125°C. To ensure full-spec timing compliance, keep total output capacitance (trace + receiver input + probe) ≤50 pF. Larger loads require buffer staging or layout optimization.

Can SN74HCS238QBQBRQ1 operate reliably at 2.5 V supply voltage?

Yes, SN74HCS238QBQBRQ1 is fully specified from 2 V to 6 V. At 2.5 V, it maintains guaranteed VT+ (0.95 V min) and VT− (0.55 V min), providing 0.4 V hysteresis for noise rejection. Propagation delay increases to 33 ns (typical), and output drive reduces to ±2.5 mA, but all logic thresholds and functionality remain valid per Recommended Operating Conditions.

How should unused inputs be terminated on SN74HCS238QBQBRQ1?

All unused inputs (A0–A2, G0–G2) on SN74HCS238QBQBRQ1 must be tied to a defined logic level - either VCC or GND - using direct connection or a 10-kΩ pull-up/down resistor. Floating inputs cause undefined output states and increased ICC due to internal shoot-through current. Schmitt-trigger inputs do not require fast edge rates, but static termination is mandatory for functional stability and EMI control.

Does SN74HCS238QBQBRQ1 support cascading with identical devices?

Yes, SN74HCS238QBQBRQ1 supports cascading via its three strobe inputs: G2 (active-high) and G1/G0 (active-low). For example, one device's Y0 output can drive G2 of a second device to expand decoding to 3-to-64 lines. This architecture avoids fanout limitations and ensures synchronized enable/disable behavior across stages, preserving timing integrity in multi-layer memory or I/O hierarchies.

Is the thermal pad on SN74HCS238QBQBRQ1 required to be soldered to ground?

No - the thermal pad on SN74HCS238QBQBRQ1 may be connected to GND or left electrically floating, per TI's datasheet guidance. Connecting it to GND improves thermal performance (RθJB = 74.4°C/W vs. ~85°C/W if unconnected) and provides additional ESD discharge path, but it must never be connected to VCC or signal nets. Mechanical anchoring via solder paste is recommended for assembly reliability regardless of electrical connection.