HT45F77 datasheet(104/203 Pages) HOLTEK

104 / 203 page

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HT45F77

Body Fat Scale Flash MCU

HT45F77

Body Fat Scale Flash MCU

Analog to Digital Converter – ADC

Theneedtointerfacetorealworldanalogsignalsisacommonrequirementformanyelectronic

systems.However,toproperlyprocessthesesignalsbyamicrocontroller,theymustfirstbe

convertedintodigitalsignalsbyA/Dconverters.ByintegratingtheA/Dconversionelectronic

circuitryintothemicrocontroller,theneedforexternalcomponentsisreducedsignificantlywiththe

correspondingfollow-onbenefitsoflowercostsandreducedcomponentspacerequirements.

A/D Data Rate Definition

Thedelta-sigmaADCdataratecanbecalculatedbytheequationlistbelow:

DataRate=(ADCclock)/(FLMS[2:0]×ADOR[2:0])

WhereADCclockcomesfromfMCLK,andFLMS[2:0]selectADCmodeanddefineaconstant

numberwhichcanonlybe30or12,finallyADOR[2:0]definechopperaveragefunctionandOver-

SamplingRating(OSR).

Forexample,ifadatarateof10Hzisdesired.Youcanhavea4.8MHzADCclock,thenset

FLMS[2:0]=000b(ADCoutputinnormalmodeandclockdividedby30);finallysetADOR[2:0]=

001btodefinechopper=2andOSR=8192.

ThusDataRate=4.8MHz/(30×2×8192)=10Hz

Inaddition,theA/Dconvertercanprovideadatarateof3.2kHztouseforautopoweron.

A/D Overview

Thisdevicecontainsahighaccuracymulti-channel20-bitdelta-sigmaanalog-to-digital(ΔΣA/D)

converterwhichcandirectlyinterfacetoexternalanalogsignals,suchasthatfromsensorsorother

controlsignalsandconvertthesesignalsdirectlyintoa20-bitdigitalvalue.

Inaddition,thePGAgaincontrol,ADCgaincontrolandADCreferencegaincontroldetermine

theamplificationgainforADCinputsignal.Thedesignercanselectthebestgaincombinationfor

thedesiredamplificationappliedtotheinputsignal.Thefollowingblockdiagramillustratesthe

ADCbasicoperationalfunction.TheADCinputchannelcanbearrangedastwodifferentialinput

channels.TheinputsignalcanbeamplifiedbyPGAbeforeenteringthe20-bitdelta-sigmaADC.

TheΔΣADCmodulatorwilloutputonebitconverteddatatoSINCfilterwhichcantransformthe

convertedone-bitdatato20bitsandstorethemintothespecificdataregisters.Additionally,this

devicealsoprovidesatemperaturesensortocompensatetheA/Dconverterdeviationcausedbythe

temperature.Withhighaccuracyandperformance,thisdeviceisverysuitablefortheWeightScale

relatedproducts.

HT45F77 Datasheet(PDF) 104 Page - Holtek Semiconductor Inc