9 Application and Implementation

Note

Information in the following applications sections is not part of the TI component specification, and

TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining

suitability of components for their purposes. Customers should validate and test their design

implementation to confirm system functionality.

9.1 Application Information

The SN74HCS238 is used to control multiple devices that operate on a shared data bus. A decoder provides the

capability to have a binary encoded input activate only one of the device's outputs. This is ideal for solid state

memory applications where multiple devices have to be read or written to with a limited number of GPIO pins

used on the system controller. The decoder is used to activate the chip select (CS) input to the selected memory

device, and the controller can then read or write from that device alone when using a shared bus.

9.2 Typical Application

CONTROL

LOGIC

System

Controller

Device 1

Device 2

Device 3

Device 4

Device 5

Device 6

Data Bus

Device 7

Device 8

Figure 9-1. Typical application block diagram

9.2.1 Design Requirements

9.2.1.1 Power Considerations

Ensure the desired supply voltage is within the range specified in the Recommended Operating Conditions. The

supply voltage sets the device's electrical characteristics as described in the Electrical Characteristics.

The positive voltage supply must be capable of sourcing current equal to the total current to be sourced by all

any transient current required for switching. The logic device can only source as much current as is provided by

Maximum Ratings.

The ground must be capable of sinking current equal to the total current to be sunk by all outputs of the

current required for switching. The logic device can only sink as much current as can be sunk into its ground

connection. Be sure not to exceed the maximum total current through GND listed in the Absolute Maximum

Ratings.

The SN74HCS238 can drive a load with a total capacitance less than or equal to 50 pF while still meeting all of

the datasheet specifications. Larger capacitive loads can be applied, however it is not recommended to exceed

50 pF.

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SN74HCS238

SCLS835B – OCTOBER 2020 – REVISED MAY 2021

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