8 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, as well as validating and testing their design

implementation to confirm system functionality.

8.1 Application Information

In this application, the SN74LVC166A is used to increase the number of inputs on a microcontroller. Unlike

other I/O expanders, the SN74LVC166A does not need a communication interface for control. It can be easily

operated with simple GPIO pins.

At power-up, the initial states of the internal shift registers are unknown. To give them a defined state of zero,

the device can be cleared by applying a low signal to the clear (CLR) input. Alternatively, data can be loaded in

directly by switching to load mode (SH/LD = low), then pulsing the clock (CLK) input once.

8.2 Typical Application

System

Controller

SER

CLK INH

SH/LD

8-Bit Shift Register

A B C D E F G H

Data Loading Gates

CLK

Control

Logic

QH

DATA[A:H]

Peripheral

CLR

Figure 8-1. Typical Application Block Diagram

8.2.1 Design Requirements

8.2.1.1 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 of the device as described in the Electrical

Characteristics section.

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

outputs of the SN74LVC166A plus the maximum static supply current, ICC, listed in the Electrical Characteristics,

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

provided by the positive supply source. Ensure the maximum total current through VCC listed in the Absolute

Maximum Ratings is not exceeded.

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

SN74LVC166A plus the maximum supply current, ICC, listed in the Electrical Characteristics, and any transient

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

connection. Ensure the maximum total current through GND listed in the Absolute Maximum Ratings is not

exceeded.

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SN74LVC166A

SCLSA15 – MAY 2024

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