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.

If the data input (D) of the D-type flip-flop 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 connected through a

Schmitt-trigger buffer to the clock input (CLK) to toggle the output.

This application also utilizes a power-on reset circuit to ensure that the output always starts in the LOW state

when power is applied.

9.2 Typical Application

Q

Q

CLR

Output

R1

PRE

R2

C1

VCC

VCC

D

CLK

VCC

R3

C2

Figure 9-1. Typical application schematic

9.2.1 Design Requirements

9.2.1.1 Power Considerations

Ensure the desired supply voltage is within the range specified in the Section 6.3. The supply voltage sets the

device's electrical characteristics as described in the Section 6.5.

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

SN74HC74 plus the maximum supply current, ICC, listed in the Section 6.5. The logic device can only source or

sink as much current as it is provided at the supply and ground pins, respectively. Be sure not to exceed the

maximum total current through GND or VCC listed in the Section 6.1.

Total power consumption can be calculated using the information provided in CMOS Power Consumption and

Cpd Calculation.

Thermal increase can be calculated using the information provided in Thermal Characteristics of Standard Linear

and Logic (SLL) Packages and Devices.

SN74HC74, SN54HC74

SCLS094F – DECEMBER 1982 – REVISED JUNE 2021

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