Texas Instruments SN74AHC238BQBR

Overview

SN74AHC238BQBR from Texas Instruments is a 3-to-8-line noninverting decoder/demultiplexer in a 16-pin WQFN (BQB) package, operating from 2V to 5.5V V_CC, with 10.5ns max propagation delay at 5V/50pF, latch-up immunity >250mA per JESD 17, and CMOS push-pull outputs. It enables memory device selection on shared data buses by decoding three address lines into eight independent chip-select signals.

For engineers reviewing the SN74AHC238BQBR datasheet, SN74AHC238BQBR pinout, SN74AHC238BQBR application, or SN74AHC238BQBR equivalent, key selection criteria include its triple strobe enable architecture (G2, G1, G0), active-high output logic, 16-pin WQFN thermal pad compatibility, and guaranteed operation across –40°C to 125°C industrial temperature range.

Technical Context

The SN74AHC238BQBR implements a positive-logic 3:8 decoder with three address inputs (A0–A2) and three independent strobe inputs: one standard (G2) and two active-low (G1, G0). Any active strobe forces all eight Y0–Y7 outputs low, enabling hierarchical cascading and demultiplexing control.

Its balanced CMOS push-pull outputs drive up to ±8mA at 5V while maintaining VOH ≥ 3.94V and VOL ≤ 0.36V under load, and its standard CMOS inputs require fast transitions (<20ns/V at 5V) to prevent oscillation or excess power draw. The device supports simultaneous output switching with defined noise margins (VOL(P) ≤ 0.8V, VOH(V) ≥ 4.4V).

Key Specifications

Pinout & Package

SN74AHC238BQBR uses a 16-pin WQFN package (BQB) with 3.5mm × 2.5mm body size and exposed thermal pad. The pad may be connected to GND or left floating; it must not connect 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 SN74HC238PW and 74LVC138AD,118, SN74AHC238BQBR uniquely delivers 5V-tolerant operation, active-high outputs, and sub-11ns delay in a thermally enhanced WQFN package - making it optimal for mixed-voltage industrial controllers requiring timing precision and ruggedness.

Availability

SN74AHC238BQBR is available at Aetrix Electronics and suitable for memory address decoding, shared-bus chip select, and industrial I/O multiplexing requiring stable component supply across automotive, industrial automation, and embedded computing programs.

Supply support for SN74AHC238BQBR 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, embedded processing, and logic solutions, with decades of leadership in high-reliability logic families.

SN74AHC238BQBR belongs to the AHC (Advanced High-Speed CMOS) logic family, designed for industrial and automotive applications demanding low power, high speed, and wide supply voltage tolerance (2V–5.5V).

FAQ

What is the maximum capacitive load SN74AHC238BQBR can drive while meeting datasheet timing specifications?

SN74AHC238BQBR is specified to meet all timing and voltage specifications with a total load capacitance ≤50pF at V_CC = 5V. Driving larger loads increases propagation delay and may degrade VOL/VOH margins. For loads exceeding 50pF, buffer stages or layout optimization (shorter traces, reduced parallel stubs) are recommended. The SN74AHC238BQBR datasheet confirms 10.5ns max t_PHL/t_PLH is guaranteed only at CL = 50pF.

Does SN74AHC238BQBR support 3.3V-only operation, and what are the key electrical parameters at that voltage?

Yes, SN74AHC238BQBR operates fully across 2V–5.5V, including 3.3V nominal systems. At V_CC = 3.3V ±0.3V, it delivers t_PHL/t_PLH ≤13ns (CL = 15pF), I_OH/I_OL = ±4mA, V_IH ≥ 2.1V, and V_IL ≤ 0.9V - ensuring interoperability with 3.3V microcontrollers and FPGAs without level translation.

How should unused inputs on SN74AHC238BQBR be terminated to ensure reliable operation?

All unused inputs (A0–A2, G0, G1, G2) on SN74AHC238BQBR must be terminated to a valid logic level - either V_CC or GND - to prevent floating states that cause excessive current draw, oscillation, or undefined outputs. 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 signals.

Can the thermal pad on the SN74AHC238BQBR (BQB package) be left unconnected, or must it be soldered to ground?

The thermal pad on SN74AHC238BQBR may be left floating or connected to GND - both configurations are explicitly permitted in the datasheet. Connecting it to GND improves thermal performance (reducing R_θJB from 75.4°C/W to lower effective values) and enhances mechanical stability, but floating is acceptable if PCB layout constraints prohibit grounding.

What is the functional difference between the G2, G1, and G0 strobe inputs on SN74AHC238BQBR?

G2 is an active-high strobe: when low, all outputs (Y0–Y7) are forced low. G1 and G0 are active-low strobes: when high, they permit normal decoding; when either is low, all outputs go low. This triple-strobe architecture enables flexible enable hierarchies - e.g., G2 for global disable, G1 for group enable, G0 for individual chip select - all implemented within a single SN74AHC238BQBR device.