HT45F3W datasheet(138/167 Pages) HOLTEK

138 / 167 page

Rev. 1.50

138

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Rev. 1.50

139

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HT45F3W

R-Type Blood Pressure Meter Flash MCU

HT45F3W

R-Type Blood Pressure Meter Flash MCU

Sensor Constant Current Generator Circuit

Thedeviceincludesaconstantcurrentgeneratorfordrivingthepressurebridgesensor.Thisis

formedusingaprogrammablevoltagereferenceandoperationalamplifier.

Constant Current Generator Operation

TheconstantcurrentgeneratormustbefirstenabledbysettingtheCCVREFENbitinthe

CCVREFCregisterhigh.Ifclearedtozerothenthecircuitswillbepowereddown,whichwillbe

animportantconsiderationinbatterypoweredequipment.TheVCCREFcircuitoutputvoltagecan

beselectedtobebetween0.2V~0.95V,inintervalsof0.05V,providing16selectionsusingbitsin

theCCVREFCregister.ThisvoltageisavailableonpinCCVREFtowhichacapacitorshouldbe

connectedforstabilisationpurposes.Thisvoltageisprovidedtothepositiveinputofaninternal

operationalamplifier.Byconnectinganexternalresistortothenegativeoperationalamplifierinput,

aconstantcurrentcanbesetup.

CCVIN

CCVIP

MCU

OPA

VCCREF

0.�V~0.95V

CCVREF

Constant Current Generator Block Diagram

HT45F3W Datasheet(PDF) 138 Page - Holtek Semiconductor Inc