Texas Instruments SN74HCS238BQBR

Overview

SN74HCS238BQBR from Texas Instruments is a 3-to-8 line decoder/demultiplexer with Schmitt-trigger inputs, designed for memory address decoding and data routing in industrial and automotive systems. It operates from 2 V to 6 V, delivers ±7.8 mA output drive at 6 V, supports –40°C to +125°C ambient temperature, and features three active-low strobe inputs (G₀, G₁) plus one standard strobe (G₂) for cascading and demux control.

For engineers reviewing the SN74HCS238BQBR datasheet, SN74HCS238BQBR pinout, SN74HCS238BQBR application, or SN74HCS238BQBR equivalent, key selection criteria include Schmitt-trigger noise immunity, low ICC (100 nA typical), WQFN-16 package thermal performance (RθJA = 108.4°C/W), and precise 3-bit address decoding with output enable gating.

Technical Context

The SN74HCS238BQBR implements a high-speed CMOS 3:8 decoder with balanced push-pull outputs and Schmitt-trigger input architecture providing hysteresis (ΔVT = 0.6 V min at 6 V). Its functional modes are fully defined by three address inputs (A₀–A₂) and three strobes (G₂, G₁, G₀), where any active strobe forces all eight outputs (Y₀–Y₇) low.

It uses silicon-gate CMOS technology with input leakage ≤ ±100 nA and supply current ICC ≤ 2 µA max across –40°C to +125°C. Propagation delay is 7 ns typical (6 V, CL = 50 pF), and output transition time tt is 4 ns typical under same conditions - enabling reliable operation in noisy, slow-slew environments without external filtering.

Key Specifications

Pinout & Package

SN74HCS238BQBR is housed in a 16-pin WQFN package (3.50 mm × 2.50 mm, 0.5 mm pitch) with an 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 SN74HC238DR and SN74HCS238PW, the SN74HCS238BQBR offers the lowest thermal resistance (108.4°C/W) and smallest footprint (3.5 mm × 2.5 mm), making it optimal for thermally demanding, high-density automotive and industrial modules where board area and junction temperature are critical constraints.

Availability

SN74HCS238BQBR is available at Aetrix Electronics and suitable for automotive body control modules, industrial PLC I/O expansion, and battery-powered sensor hubs requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN74HCS238BQBR 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 logic solutions, with decades of automotive and industrial qualification expertise.

The SN74HCS238BQBR belongs to TI's HCS logic family - engineered for high noise immunity, ultra-low static power, and extended temperature operation in harsh-environment control systems.

FAQ

What is the function of the G₂, G₁, and G₀ inputs on the SN74HCS238BQBR?

The SN74HCS238BQBR uses G₂ (active-high), G₁ (active-low), and G₀ (active-low) as strobe inputs to enable or disable decoded outputs. When any strobe is asserted, all Y₀–Y₇ outputs are forced low - allowing hierarchical decoding, chip-select gating, or demultiplexing. This behavior is explicitly defined in the Function Table (Table 8-1) of the datasheet and applies identically to the SN74HCS238BQBR.

Does the SN74HCS238BQBR require external pull-up or pull-down resistors on its inputs?

No - the SN74HCS238BQBR does not require external pull resistors on A₀–A₂, G₀, G₁, or G₂ because its Schmitt-trigger inputs tolerate floating states without latch-up or excessive current. However, TI recommends tying unused inputs to VCC or GND for predictable operation; a 10-kΩ resistor is typical if dynamic control is needed later. This guidance is confirmed in Section 9.2.1.2 of the datasheet.

Can the SN74HCS238BQBR drive a 50-pF capacitive load while meeting timing specifications?

Yes - the SN74HCS238BQBR's switching characteristics (Section 6.6) are specified with CL = 50 pF, delivering 7 ns typical propagation delay at 6 V. Driving loads ≤ 50 pF ensures full compliance with tpd, tt, and VOH/VOL limits. Exceeding 50 pF increases delay and may degrade noise margin - per Section 9.2.1.1 design guidance.

Is the thermal pad on the SN74HCS238BQBR package required to be connected to ground?

No - the thermal pad on the SN74HCS238BQBR (WQFN-16) may be connected to GND or left electrically floating, as stated in Table 5-1 (Pin Functions) and Section 5. TI explicitly cautions against connecting it to any signal or supply other than GND. Grounding improves thermal performance (RθJB drops to 74.4°C/W) and EMI suppression but is not mandatory for functionality.

How does the SN74HCS238BQBR differ from the older SN74HC238 in terms of input structure?

The SN74HCS238BQBR integrates Schmitt-trigger inputs (with 0.6 V hysteresis at 6 V), whereas the SN74HC238 uses standard CMOS inputs. This gives the SN74HCS238BQBR superior noise rejection and tolerance for slow-rising signals - critical in automotive and industrial settings. Electrical Characteristics tables (Sections 6.5 and 8.3.2) confirm this architectural difference applies specifically to the SN74HCS238BQBR.