Texas Instruments SN74HCS238DYYR

Overview

SN74HCS238DYYR from Texas Instruments is a 3-to-8 line decoder/demultiplexer with Schmitt-trigger inputs, designed for memory address decoding and data routing in noise-prone or slow-slew environments. 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 strobes (G₀, G₁) and one standard strobe (G₂) for cascading and demux control.

For engineers reviewing the SN74HCS238DYYR datasheet, SN74HCS238DYYR pinout, SN74HCS238DYYR application, or SN74HCS238DYYR equivalent, key selection criteria include Schmitt-trigger hysteresis (ΔVT = 0.6–1.6 V), low ICC (100 nA typical), 16-pin SOT-23-THN package compatibility, and functional behavior under partial strobe activation in industrial bus-select systems.

Technical Context

The SN74HCS238DYYR implements a high-speed silicon-gate CMOS 3:8 decoder with balanced push-pull outputs and Schmitt-trigger input architecture. Its three address inputs (A₀–A₂) select one of eight outputs (Y₀–Y₇), while three strobe inputs (G₂, G₁, G₀) gate all outputs to low when asserted - enabling hierarchical decoding and demultiplexing functions.

Strobe logic follows active-low priority: any active G₀ or G₁ forces all outputs low regardless of A₀–A₂ state; G₂ is active-high and enables normal decode only when G₀ and G₁ are both inactive. Output states are low by default and go high only on selection - eliminating floating outputs and simplifying bus arbitration in shared-data applications.

Key Specifications

Pinout & Package

SOT-23-THN (16-pin) package with 4.20 mm × 2.00 mm body size, optimized for space-constrained PCB layouts and automated placement. Thermal pad is not present - no thermal pad connection required.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCS238DYYR, SN74HC238DR offers mechanical compatibility with legacy SOIC footprints but sacrifices board area efficiency, while SN74HCS138PWR provides identical performance in TSSOP-16 but demands strobe signal inversion - making SN74HCS238DYYR optimal for new space- and noise-sensitive designs requiring SOT-23-THN integration.

Availability

SN74HCS238DYYR is available at Aetrix Electronics and suitable for industrial automation, automotive subsystem control, and battery-powered IoT edge nodes requiring stable component supply, extended temperature resilience, and noise-immune digital decoding.

Supply support for SN74HCS238DYYR 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 delivering analog, embedded processing, and connectivity solutions for industrial, automotive, and consumer markets.

The SN74HCS238DYYR belongs to TI's HCS logic family - engineered for high-noise immunity and ultra-low static power in harsh-environment digital control systems.

FAQ

What is the maximum capacitive load the SN74HCS238DYYR can drive while maintaining specified timing?

The SN74HCS238DYYR is characterized for CL = 50 pF in its switching characteristics table. At this load, propagation delay remains ≤16 ns (max) at 6 V and 125°C. Driving larger capacitances increases tpd nonlinearly and may violate setup/hold margins in synchronous systems; TI recommends limiting total output node capacitance to 50 pF unless re-characterized for the specific application. The SN74HCS238DYYR datasheet specifies this value in Section 6.6.

Can unused inputs on the SN74HCS238DYYR be left floating?

No - unused inputs on the SN74HCS238DYYR must be terminated to VCC or GND using direct connection or a pull-up/down resistor (e.g., 10 kΩ). Floating inputs cause undefined logic states, increased ICC, and potential oscillation due to internal metastability. This requirement applies to all address (A₀–A₂) and strobe (G₀–G₂) inputs not actively driven in the design. The SN74HCS238DYYR datasheet explicitly mandates this in Section 9.2.1.2.

Does the SN74HCS238DYYR support hot insertion or live plugging?

No - the SN74HCS238DYYR lacks hot-swap protection circuitry. Applying VCC before GND, or connecting inputs before power stabilization, risks exceeding absolute maximum ratings (e.g., VI > VCC + 0.5 V) and triggering clamp diode conduction. TI specifies strict power sequencing: GND must be established first, then VCC, followed by input signals. This requirement is documented in Section 6.1 and Section 8.3.3 of the SN74HCS238DYYR datasheet.

How does the Schmitt-trigger hysteresis of the SN74HCS238DYYR improve noise immunity in automotive applications?

The SN74HCS238DYYR provides ΔVT = 0.6 V (min) at 6 V supply, meaning input signals must swing at least 600 mVpp between valid LOW and HIGH thresholds. This rejects common-mode noise from alternator ripple, ignition spikes, or EMI coupling on long harness runs - preventing false decoding during engine cranking or load dump events. Unlike standard CMOS inputs, Schmitt-trigger inputs do not require external RC filtering, simplifying design. This behavior is quantified in Table 6-5 of the SN74HCS238DYYR datasheet.

Is the SN74HCS238DYYR pin-compatible with the older SN74LS238?

No - the SN74HCS238DYYR is not pin-compatible with SN74LS238. While both are 3-to-8 decoders, SN74LS238 uses TTL logic levels, different strobe polarity (G₁/G₂ active-high), and a 16-pin PDIP/SOIC footprint incompatible with SOT-23-THN. Electrical differences include VIL/VIH thresholds, output drive strength, and supply voltage range (SN74LS238 requires 5 V only). Direct replacement would require PCB redesign and firmware logic adjustment. This incompatibility is confirmed by TI's logic cross-reference documentation for SN74HCS238DYYR.