HT45F4630 datasheet(39/153 Pages) HOLTEK

39 / 153 page

Rev. 1.00

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Rev. 1.00

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HT45F4630

DC Motor Driver ASSP MCU

HT45F4630

DC Motor Driver ASSP MCU

External 32.768kHz Crystal Oscillator – LXT

TheExternal32.768kHzCrystalSystemOscillatorisoneofthelowfrequencyoscillatorchoices,

whichisselectedviaconfigurationoption.Thisclocksourcehasafixedfrequencyof32.768kHz

andrequiresa32.768kHzcrystaltobeconnectedbetweenpinsXT1andXT2.Theexternalresistor

andcapacitorcomponentsconnectedtothe32.768kHzcrystalarenecessarytoprovideoscillation.

Forapplicationswhereprecisefrequenciesareessential,thesecomponentsmayberequiredto

providefrequencycompensationduetodifferentcrystalmanufacturingtolerances.Duringpower-up

thereisatimedelayassociatedwiththeLXToscillatorwaitingforittostart-up.

WhenthemicrocontrollerenterstheSLEEPorIDLEMode,thesystemclockisswitchedofftostop

microcontrolleractivityandtoconservepower.However,inmanymicrocontrollerapplications

itmaybenecessarytokeeptheinternaltimersoperationalevenwhenthemicrocontrollerisin

theSLEEPorIDLEMode.Todothis,anotherclock,independentofthesystemclock,mustbe

provided.

However,forsomecrystals,toensureoscillationandaccuratefrequencygeneration,itisnecessary

toaddtwosmallvalueexternalcapacitors,C1andC2.TheexactvaluesofC1andC2should

beselectedinconsultationwiththecrystalorresonatormanufacturerspecification.Theexternal

parallelfeedbackresistor,RP,isrequired.

SomeconfigurationoptionsdetermineiftheXT1/XT2pinsareusedfortheLXToscillatororas

normalI/Oorotherpin-sharedfunctionalpins.

• IftheLXToscillatorisnotusedforanyclocksource,theXT1/XT2pinscanbeusedasnormalI/O

orotherpin-sharedfunctionalpins.

• IftheLXToscillatorisusedforanyclocksource,the32.768kHzcrystalshouldbeconnectedto

theXT1/XT2pins.

Foroscillatorstabilityandtominimisetheeffectsofnoiseandcrosstalk,itisimportanttoensure

thatthecrystalandanyassociatedresistorsandcapacitorsalongwithinterconnectinglinesareall

locatedasclosetotheMCUaspossible.

Note: 1. RP� C1 and C� a�e �equi�ed.

�. ��though not shown �ins have a �a�asitic ca�acitance of a�ound 7�F.

To inte�na�

ci�cuits

Internal

Oscillator

Circuit

C�

XT1

XT�

3�.7�8kHz

Inte�na� RC

Osci��ato�

External LXT Oscillator

LXT Oscillator C1 and C2 Values

Crystal Frequency

3�.7�8kHz

10�F

Note: 1. C1 and C� va�ues a�e fo� guidance on�y.

�. RP=5M~10MΩ is recommended.

32.768kHz Crystal Recommended Capacitor Values

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