HT45F75 datasheet(109/190 Pages) HOLTEK

109 / 190 page

Rev. 1.10

108

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Rev. 1.10

109

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HT45F75

Body Fat Scale Flash MCU

HT45F75

Body Fat Scale Flash MCU

A/D Transfer Function

Thisdevicecontainsa20-bitΔΣA/Dconverter,itsfull-scaleconverteddigitisedvalueisfrom

524287to-524288indecimalvalue.Theconverteddataformatisformedbyatwo’scomplement

binaryvalue.TheMSBoftheconverteddataisthesignedbit.Sincethefull-scaleanaloginput

valueisequaltotheVCMor∆VREFvoltage,selectedbytheVREFSbitinADCR0register,thisgives

asinglebitanaloginputvalueofVCMor∆VREFdividedby524288.

1LSB=(VCMor∆VREF)/524288

TheA/DConverterinputvoltagevaluecanbecalculatedusingthefollowingequation:

ΔSI_I=(PGAGN×ADGN×ΔDI±)+(DCSET×ΔVR_I)

ΔVR_I=VREGN×ΔVR±

ADC_Conversion_Data=(ΔSI_I÷ΔVR_I)×K

WhereKisequalto219

Note:ThePGAGN,ADGN,VREGNvaluesaredecidedbyPGS,AGS,VGScontrolbits.

∆SI_I:DifferentialInputSignalafterprocess

PGAGN:ProgrammableGainAmplifiergain

ADGN:ADCgain

∆DI±:DifferentialInputsignal

DCSET:Offsetvoltage

∆VR±:DifferentialReferencevoltage

∆VR_I:DifferentialReferenceinputvoltageafterprocess

VREGN:Referencevoltagegain

DuetothedigitalsystemdesignoftheΔΣADC,themaximumnumberoftheADCconvertedvalue

is524287andtheminimumvalueis-524288,therefore,wecanhavethemiddlenumber0.The

ADC_Conversion_Dataequationillustratesthisrangeofconverteddatavariation.

A/D conversion data

(2’s compliment, Hexadecimal)

Decimal Value

0x7FFFF

5��87

0x80000

-5��88

TheaboveADCconversiondatatableillustratestherangeofADCconversiondata.

ThefollowingdiagramshowstherelationshipbetweentheDCinputvalueandtheADCconverted

datawhichispresentedbytheTwo’sComplement.

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