OC

PG

ON/OFF

RESET

Power Supply

Motor Controller

On/Off Switch

Over

Temp

Detection

Over Current

Detection

OT

9

SN74HCS08

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SCLS778A – DECEMBER 2019 – REVISED MAY 2020

Product Folder Links: SN74HCS08

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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

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

Figure 9. 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

Figure 9. Typical application block diagram

9.2.1 Design Requirements

•

All signals in the system operate at 5 V

•

The motor controller should be disabled if any of these conditions apply:

–

Power Supply is not ready (PG)

–

Excessive current is detected (OC)

–

Excessive temperature is detected (OT)

–

The power switch is in the OFF position (ON/OFF)

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

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