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, as well as validating and testing their design

implementation to confirm system functionality.

9.1 Application Information

Toggle switches are typically large, mechanically complex and relatively expensive. It is desirable to use a

momentary switch instead because they are small, mechanically simple and low cost. Some systems require

a toggle switch's functionality but are space or cost constrained and must use a momentary switch instead.

The SN74HCS74-Q1 has integrated Schmitt-trigger inputs that eliminate the need for a second IC for signal

conditioning, reducing the required board space. This makes the SN74HCS74-Q1 an ideal device for converting

a momentary switch into a toggle switch.

If the data input (D) of the SN74HCS74-Q1 is tied to the inverted output ( Q), then each clock pulse will cause

the value at the output (Q) to toggle. The momentary switch can be debounced and directly connected to the

clock input (CLK) to toggle the output.

9.2 Typical Application

Q

Q

CLR

Output

PRE

D

CLK

GND

Figure 9-1. Device Power Button Circuit

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

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

Absolute 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.

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SN74HCS74-Q1

SCES894E – APRIL 2019 – REVISED DECEMBER 2021

Copyright © 2021 Texas Instruments Incorporated

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