HT45F2020 datasheet(59/85 Pages) HOLTEK

59 / 85 page

Rev. 1.00

April 11, 2017

Rev. 1.00

April 11, 2017

HT45F2020/HT45F2022

Sound Effect Generator Flash MCU

HT45F2020/HT45F2022

Sound Effect Generator Flash MCU

Shunt Regulator – for HT45F2020 only

TheHT45F2020deviceincludesafullyintegratedshuntregulator.Thedeviceofferstheadvantages

ofafullyinternalshuntregulatorallowingittobeusedwithawiderangeofexternalpower

supplyvoltageswiththesimpleadditionofanexternalresistorandcapacitor.Theshuntregulator

isacommonandsimpletypeofregulatorwhoseoutputisusedasthedevicepowersupply.Itis

constructedofapowertransistorandavoltagefeedbackcircuit.Thepowertransistor,whoseoutput

currentiscontrolledbyavoltagefeedbackcircuit,isusedtoshunttheextracurrenttomaintaina

constantregulatedvoltageonVDD.Thispowertransistorprovidesacurrentpathfromthedevice

supplyvoltagetoground.Anexternalresistor,RSER,shouldbeproperlyselectedtoseriallyconnect

VDDtotheexternalpowersupply.Theshuntregulatormaynothavetheexpectedperformanceif

theRSERresistanceistoosmallortoolarge.AcapacitorisexternallyconnectedbetweenVDDand

VSSpinstostabilisetheregulatedvoltage.Notethatexcessivepowerdissipationinformofheat

duetotheshuntcurrentthroughthepowertransistorshouldbetakenintoconsiderationintheuser

applications.

RSER

ISUPPLY

VUNREG

VOUT

CBYPASS

ISHUNT

VDD

Feedback

VSS

ILOAD

VDD

VSS

Shunt Regulator Block Diagram – HT45F2020

Examinationoftheshuntregulatorblockdiagramwillrevealthatthesupplycurrentwillbe

determinedbythevalueoftheexternalRSERresistor.Forthisreasonselectionofthisresistorvalue

isanimportantissue.Itisrecommendedthatthefollowingcriteriaareusedwhendecidingonthe

valueofRSER.

ThevalueofRSERiscalculatedasfollows:

RSER=(VUNREG–VDD)/ISUPPLY;

WhereISUPPLY=ISHUNT(Max)≤whichshouldbelessthanorequalto80mA.

Themaximumvalueoftheloadcurrentiscalculatedasfollows:

ILOAD(Max)=ISHUNT(Max)×(VUNREG(Min)–VOUT1(Max))/(VUNREG(Max)−VOUT1(Min))−ISTATIC(Measured);

WhereVUNREG(Max),VOUT1(Max)=MaximumspecificationvalueforVUNREGandVOUT1respectively.

AndVUNREG(Min),VOUT1(Min)=MinimumspecificationvalueforVUNREGandVOUT1respectively.

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