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

In this application, three 2-input AND gates are combined to produce a 4-input AND gate function as shown in

Figure 9-1. The fourth gate can be used for another application in the system, or the inputs can be grounded and

the channel left unused.

The SN74HCS08 is used to directly control the RESET pin of a motor controller. The controller requires four

input signals to all be HIGH before being enabled, and should be disabled in the event that any one signal goes

LOW. The 4-input AND gate function combines the four individual reset signals into a single active-low reset

signal.

Many power good signals utilize open-drain outputs which can produce slow input transition rates when they

transition from LOW to Hi-Z mode. This makes the SN74HCS08 ideal for the application because it has Schmitt-

trigger inputs that do not have input transition rate requirements.

9.2 Typical Application

OC

PG

ON/OFF

RESET

Power Supply

Motor Controller

On/Off Switch

Over

Temp

Detection

Over Current

Detection

OT

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

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.

SN74HCS08

SCLS778B – DECEMBER 2019 – REVISED JANUARY 2021

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