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, this device 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.

9.2 Typical Application

OC

PG

CASE

ON/OFF

RESET

Power Sup ply

Motor Con trol ler

On/Off Switch

Case Tamper

Switch

Over Current

Detection

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

CD74HC21 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.

CAUTION

The maximum junction temperature, TJ(max) listed in the Section 6.1, is an additional limitation to

prevent damage to the device. Do not violate any values listed in the Section 6.1. These limits are

provided to prevent damage to the device.

CD74HC21, CD54HC21

SCHS131D – AUGUST 1997 – REVISED MAY 2021

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