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LTC3857EUHPBF Datasheet(PDF) 8 Page - Linear Technology |
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LTC3857EUHPBF Datasheet(HTML) 8 Page - Linear Technology |
8 / 38 page LTC3857 3857fa pin FuncTions SENSE1–, SENSE2– (Pin 1, Pin 9):The(–)Inputtothe Differential Current Comparators. When greater than INTVCC–0.5V,theSENSE–pinsuppliescurrenttothe currentcomparator. FREQ (Pin 2):Thefrequencycontrolpinfortheinternal VCO.ConnectingthepintoGNDforcestheVCOtoafixed lowfrequencyof350kHz.ConnectingthepintoINTVCC forces the VCO to a fixed high frequency of 535kHz. Other frequencies between 50kHz and 900kHz can be programmedusingaresistorbetweenFREQandGND. Aninternal20µApull-upcurrentdevelopsthevoltageto beusedbytheVCOtocontrolthefrequency PHASMD (Pin 3):ControlInputtoPhaseSelectorwhich determines the phase relationships between control- ler1, controller 2 and the CLKOUT signal. Pulling this pintogroundforcesTG2andCLKOUTtobeoutofphase 180°and60°withrespecttoTG1.Connectingthispinto INTVCCforcesTG2andCLKOUTtobeoutofphase240° and120°withrespecttoTG1.FloatingthispinforcesTG2 andCLKOUTtobeoutofphase180°and90°withrespect toTG1.RefertoTable1. CLKOUT (Pin 4):Outputclocksignalavailabletodaisy- chainothercontrollerICsforadditionalMOSFETdriver stages/phases.TheoutputlevelsswingfromINTVCCto ground. PLLIN/MODE (Pin 5):ExternalSynchronizationInputto PhaseDetectorandForcedContinuousModeInput.When anexternalclockisappliedtothispin,thephase-locked loopwillforcetherisingTG1signaltobesynchronized with the rising edge of the external clock. When not synchronizingtoanexternalclock,thisinput,whichacts onbothcontrollers,determineshowtheLTC3857operates at light loads. Pulling this pin to ground selects Burst Modeoperation.Aninternal100kresistortogroundalso invokesBurstModeoperationwhenthepinisfloated. TyingthispintoINTVCCforcescontinuousinductorcurrent operation.Tyingthispintoavoltagegreaterthan1.2Vand lessthanINTVCC–1.3Vselectspulse-skippingoperation. Thiscanbedonebyaddinga100kresistorbetweenthe PLLIN/MODEpinandINTVCC. SGND (Pin 6, Exposed Pad Pin 33):Small-signalground commontobothcontrollers,mustberoutedseparately fromhighcurrentgroundstothecommon(–)terminals oftheCINcapacitors.Theexposedpadmustbesoldered tothePCBforratedthermalperformance. RUN1, RUN2 (Pin 7, Pin 8):DigitalRunControlInputsfor EachController.Forcingeitherofthesepinsbelow1.26V shutsdownthatcontroller.Forcingbothofthesepinsbelow 0.7VshutsdowntheentireLTC3857,reducingquiescent currenttoapproximately8µA.Donotfloatthesepins. INTVCC(Pin19):OutputoftheInternalLinearLowDropout Regulator. The driver and control circuits are powered fromthisvoltagesource.Mustbedecoupledtopower groundwithaminimumof4.7µFceramicorotherlow ESRcapacitor.DonotusetheINTVCCpinforanyother purpose. EXTVCC (Pin 20):ExternalPowerInputtoanInternalLDO ConnectedtoINTVCC.ThisLDOsuppliesINTVCCpower, bypassingtheinternalLDOpoweredfromVINwhenever EXTVCCishigherthan4.7V.SeeEXTVCCConnectionin theApplicationsInformationsection.Donotexceed14V onthispin. PGND (Pin 21):DriverPowerGround.Connectstothe sourcesofbottom(synchronous)N-channelMOSFETs andthe(–)terminal(s)ofCIN. VIN (Pin 22):MainSupplyPin.Abypasscapacitorshould betiedbetweenthispinandthesignalgroundpin. BG1, BG2 (Pin 23, Pin 18): High Current Gate Drives forBottom(Synchronous)N-ChannelMOSFETs.Voltage swingatthesepinsisfromgroundtoINTVCC. BOOST1,BOOST2(Pin24,Pin17):BootstrappedSupplies totheTopsideFloatingDrivers.Capacitorsareconnected betweentheBOOSTandSWpinsandSchottkydiodesare tiedbetweentheBOOSTandINTVCCpins.Voltageswing attheBOOSTpinsisfromINTVCCto(VIN+INTVCC). SW1, SW2 (Pin 25, Pin 16):SwitchNodeConnections toInductors. |
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