SN74HCS138QBQBRQ1

Overview

The SN74HCS138QBQBRQ1 is an automotive-qualified, high-speed silicon gate CMOS decoder featuring three address select inputs and eight active-low outputs. It operates within a supply voltage range of 2 V to 6 V and supports temperatures from -40°C to +125°C. The device utilizes Schmitt-trigger inputs for noise tolerance and includes balanced push-pull outputs capable of ±7.8-mA drive at 6 V. Propagation delays range from 7 ns to 22 ns depending on voltage and temperature. It is housed in a 16-pin WQFN (WBQB) package with wettable flanks.

Feature Summary

• AEC-Q100 qualified for automotive applications with specified temperature grades and ESD protection levels.
• Schmitt-trigger inputs provide enhanced noise rejection and support slow or noisy input signal transitions.
• Balanced CMOS push-pull outputs ensure similar sourcing and sinking current capabilities for robust driving.
• Wettable flank QFN package design facilitates improved side soldering and reliable automatic optical inspection.

Applications

• Memory device selection utilizing shared data buses
• Reducing the required number of outputs for chip select applications
• Routing data signals across multiple channels

Procurement Notes

Verify that the specific WBQB package variant matches the intended PCB footprint and thermal requirements. Confirm AEC-Q100 qualification aligns with project grade specifications. Ensure input termination strategies account for Schmitt-trigger characteristics to prevent undefined states. Validate power supply decoupling practices against the recommended layout guidelines to maintain signal integrity.

Selection Notes

Select this component when automotive reliability and wide voltage operation are required. The Schmitt-trigger inputs make it suitable for noisy environments or slow signal edges. Consider the WQFN package for compact designs requiring effective thermal dissipation and inspection visibility. Verify that the output drive strength meets the load requirements without exceeding absolute maximum ratings.

Part Context

This part belongs to the SN74HCS138-Q1 family of 3-to-8 line decoders/demultiplexers. It shares functional similarities with other HCS series logic devices but is specifically optimized for automotive use. The WBQB suffix denotes the wettable flank WQFN package, distinguishing it from standard QFN or SOIC variants within the same logical family.

Replacement Considerations

SN74HCS138DYYRQ1

FAQ

How do Schmitt-trigger inputs affect power consumption during slow transitions?

Driving inputs with slow transitioning signals increases dynamic current consumption. However, holding an input at a valid non-supply value does not cause huge increases in static power consumption compared to standard CMOS inputs.

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

The strobe inputs simplify cascading and facilitate demultiplexing. When any strobe input is active, all outputs are forced into the high state. When disabled, only the selected output goes low.

Can unused outputs be connected directly to VCC or ground?

No. Unused outputs should be left floating. Connecting them directly to VCC or ground can cause excessive current flow and damage the device due to the push-pull output structure.