Texas Instruments SN74AHC238QPWRQ1

Overview

SN74AHC238QPWRQ1 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 across 2V–5.5V supply, delivering ≤10.5ns propagation delay at 5V/50pF, and qualified per AEC-Q100 Grade 1 (−40°C to +125°C) for memory selection and bus routing in engine control units and ADAS domain controllers.

For engineers reviewing the SN74AHC238QPWRQ1 datasheet, SN74AHC238QPWRQ1 pinout, SN74AHC238QPWRQ1 application, or SN74AHC238QPWRQ1 equivalent, key selection considerations include strobe-controlled output gating, wettable-flank WQFN-16 package compatibility with AOI inspection, latch-up immunity (>250mA), and CMOS input transition rate compliance (≤20 ns/V at 5V).

Technical Context

The SN74AHC238QPWRQ1 implements a positive-logic 3:8 decoder with three address inputs (A₀–A₂) and three independent strobe controls: G₂ (active-high), G₁ and G₀ (both active-low). When any strobe is asserted, all eight outputs (Y₀–Y₇) are forced low; only the selected output goes high when strobes are inactive.

Its balanced CMOS push-pull outputs support ±8mA drive at 5V, while standard CMOS inputs require VIH ≥3.85V and VIL ≤1.65V at VCC = 5.5V and tolerate ≤20 ns/V input slew rates. The device features integrated clamp diodes on all I/O pins and supports cascading via strobe chaining for larger decode trees.

Key Specifications

Pinout & Package

SN74AHC238QPWRQ1 is packaged in a 16-pin wettable-flank QFN (BQB), 3.5mm × 2.5mm body size, with exposed thermal pad (connectable to GND). This package enables automated optical inspection (AOI) of solder joints and improves 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 SN74LV238APWR and MC74VHC238DT, SN74AHC238QPWRQ1 uniquely delivers full AEC-Q100 Grade 1 qualification, wettable-flank packaging for production traceability, and 10.5ns propagation delay - making it the only option certified for timing-critical, high-reliability automotive decoding where junction temperature exceeds 125°C.

Availability

SN74AHC238QPWRQ1 is available at Aetrix Electronics and suitable for engine control units, ADAS domain controllers, and body control modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN74AHC238QPWRQ1 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 IC design, functional safety development, and high-reliability manufacturing.

SN74AHC238QPWRQ1 belongs to TI's AHC logic family optimized for low-power, high-speed automotive decoding - designed specifically to replace discrete transistor arrays and reduce board space in ECU and domain controller applications.

FAQ

What is the maximum capacitive load SN74AHC238QPWRQ1 can drive while maintaining specified timing?

The SN74AHC238QPWRQ1 is characterized and guaranteed to meet all switching specifications-including 10.5ns max propagation delay-at a load capacitance of 50pF. Driving loads exceeding 50pF will increase propagation delay and may degrade noise margins; TI recommends limiting total output capacitance to ≤50pF for timing-critical automotive applications. The SN74AHC238QPWRQ1 datasheet specifies performance only up to this value under recommended operating conditions.

Does SN74AHC238QPWRQ1 support cascading for larger decode functions like 4-to-16?

Yes, SN74AHC238QPWRQ1 supports cascading via its three strobe inputs (G₂, G₁, G₀). For example, two SN74AHC238QPWRQ1 devices can implement a 4-to-16 decoder: the fourth address bit selects between the two decoders by enabling one G₂ input while disabling the other. This method preserves timing integrity and leverages the device's built-in strobe gating-no external logic required. Function Table 7-1 in the SN74AHC238QPWRQ1 datasheet confirms strobe priority behavior.

Can unused inputs on SN74AHC238QPWRQ1 be left floating in automotive designs?

No. All unused inputs on SN74AHC238QPWRQ1-including A₀, A₁, A₂, G₀, G₁, and G₂-must be terminated to a valid logic level (VCC or GND) to prevent undefined states, excessive power consumption, or oscillation. TI explicitly requires this in Section 7.3.2 and Figure 8-3 of the SN74AHC238QPWRQ1 datasheet. A 10kΩ pull-up or pull-down resistor is recommended for inputs that may be inactive during certain modes.

Is the thermal pad on the SN74AHC238QPWRQ1 WQFN package required to be connected to ground?

The thermal pad on the SN74AHC238QPWRQ1 (BQB package) may be connected to GND or left electrically floating-it must never be connected to any signal or supply net other than GND. TI states in Table 4-1 that "The thermal pad can be connect to GND or left floating." Connecting to GND improves thermal dissipation and EMI performance; leaving it floating is acceptable if board layout constraints prohibit grounding, but GND connection is strongly preferred for automotive reliability.

How does the strobe logic hierarchy work in SN74AHC238QPWRQ1 when multiple strobes are asserted?

In SN74AHC238QPWRQ1, all three strobes (G₂, G₁, G₀) operate independently with OR-like gating: if *any* strobe is active-G₂ high, or G₁ low, or G₀ low-all outputs Y₀–Y₇ are forced low regardless of A₂–A₀ state. There is no priority hierarchy; simultaneous assertion of multiple strobes has identical effect as asserting just one. This behavior is confirmed in the Functional Block Diagram (Figure 7-1) and Function Table 7-1 of the SN74AHC238QPWRQ1 datasheet.