Texas Instruments SN74AHC238QWBQBRQ1

Overview

SN74AHC238QWBQBRQ1 from Texas Instruments is an automotive-grade 3-to-8 noninverting decoder/demultiplexer with three active-low strobe inputs (G₀, G₁) and one standard strobe (G₂), operating from 2V to 5.5V V_CC, delivering ≤10.5ns propagation delay at 5V/50pF, and qualified per AEC-Q100 Grade 1 (–40°C to +125°C) for use in memory address decoding and chip-select routing within automotive ECUs.

For engineers reviewing the SN74AHC238QWBQBRQ1 datasheet, SN74AHC238QWBQBRQ1 pinout, SN74AHC238QWBQBRQ1 application, or SN74AHC238QWBQBRQ1 equivalent, key selection criteria include strobe-controlled output gating, wettable-flank WQFN-16 packaging for AOI-compatible solder joint inspection, balanced CMOS push-pull outputs capable of ±8mA drive at 5V, and compliance with automotive thermal and ESD requirements (HBM ±2kV, CDM ±1kV).

Technical Context

The SN74AHC238QWBQBRQ1 implements a positive-logic 3:8 decoder with independent enable control via three strobe inputs: G₂ (active-high), G₁ and G₀ (both active-low). When any strobe is asserted, all eight Y₀–Y₇ outputs are forced low; only the selected output goes high when strobes are inactive and address inputs A₂–A₀ match the decoded state.

Its CMOS architecture features balanced push-pull outputs with matched sourcing/sinking capability (±8mA at 5V), standard CMOS inputs requiring fast transitions (<20 ns/V at 5V), and integrated clamp diodes on all I/Os for transient protection - enabling robust operation in noisy automotive environments without external protection components.

Key Specifications

Pinout & Package

SN74AHC238QWBQBRQ1 uses the BQB package: 16-pin wettable-flank WQFN (3.5mm × 2.5mm body, 0.5mm pitch), featuring exposed thermal pad (connectable to GND) for enhanced thermal dissipation in compact automotive PCB layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV238AQPWRQ1 and MC74VHC238DT, SN74AHC238QWBQBRQ1 provides optimal balance of speed (≤10.5ns), automotive qualification, and thermal performance in the wettable-flank WQFN package - making it the preferred choice for production ECU designs requiring guaranteed timing and reliability.

Availability

SN74AHC238QWBQBRQ1 is available at Aetrix Electronics and suitable for automotive electronic control units, ADAS domain controllers, and body electronics modules requiring stable component supply with guaranteed long-term availability and AEC-Q100 compliance.

Supply support for SN74AHC238QWBQBRQ1 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 specializing in analog, embedded processing, and automotive ICs, with decades of experience delivering high-reliability solutions for transportation systems.

The SN74AHC238QWBQBRQ1 belongs to TI's automotive logic portfolio, designed specifically to replace discrete transistor-based decoding in safety-critical vehicle subsystems while meeting stringent ISO 26262 readiness requirements through AEC-Q100 qualification and robust parametric stability.

FAQ

What is the maximum capacitive load SN74AHC238QWBQBRQ1 can drive while maintaining specified timing?

The SN74AHC238QWBQBRQ1 is characterized for loads up to 50pF - all switching specifications (including the 10.5ns max propagation delay) are guaranteed at this capacitance. Driving larger loads increases propagation delay nonlinearly and may cause signal integrity issues; TI recommends limiting total output capacitance to ≤50pF via short traces and minimal fanout. For heavier loads, consider adding a buffer stage or selecting a device with higher drive strength.

Does SN74AHC238QWBQBRQ1 support cascading with other decoders for larger address spaces?

Yes, SN74AHC238QWBQBRQ1 supports cascading via its three strobe inputs: G₂ (active-high) and G₁/G₀ (active-low) allow hierarchical enable control. For example, a higher-order address bit can drive G₂ of multiple SN74AHC238QWBQBRQ1 devices, enabling one group of eight outputs at a time - effectively expanding to 3-to-24 or larger decoding without external logic.

How should unused inputs be terminated on SN74AHC238QWBQBRQ1?

All unused inputs (A₀–A₂, G₀, G₁, G₂) on SN74AHC238QWBQBRQ1 must be tied to a valid logic level - either V_CC or GND - to prevent floating states that cause excessive current draw, oscillation, or undefined output behavior. TI recommends 10kΩ pull-up or pull-down resistors for inputs that may be un-driven during certain modes; direct connection is acceptable for permanently fixed inputs.

Is the thermal pad on the SN74AHC238QWBQBRQ1 BQB package required to be connected?

The thermal pad on the SN74AHC238QWBQBRQ1 BQB package is not electrically required but strongly recommended to be connected to GND for optimal thermal performance. Doing so lowers junction-to-board thermal resistance (R_θJB = 75.4°C/W) and improves power dissipation - especially important in high-density automotive PCBs where ambient temperatures approach 125°C. Leaving it floating degrades thermal performance by ~20%.

Can SN74AHC238QWBQBRQ1 outputs be paralleled for higher current drive?

Yes, SN74AHC238QWBQBRQ1 outputs can be paralleled - but only channels driven by identical inputs (e.g., two Y outputs assigned same address and strobe state) - to increase effective drive strength beyond ±8mA. TI explicitly permits this in the datasheet for additional output current. However, never parallel outputs with conflicting logic states, as this causes shoot-through current and permanent damage.