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## LT3999 Datasheet(PDF) 11 Page - Linear Technology

 Part No. LT3999 Description Low Noise, 1A, 1MHz Push-Pull DC/DC Driver with Duty Cycle Control Download 16 Pages Scroll/Zoom 100% Maker LINER [Linear Technology] Homepage http://www.linear.com Logo

## LT3999 Datasheet(HTML) 11 Page - Linear Technology

 11 / 16 page LT3999113999faFor more information www.linear.com/LT3999APPLICATIONS INFORMATIONOutput Voltage RegulationThe output voltage of the DC transformer topology isunregulated. Variations in the input voltage will causethe output voltage to vary because the output voltage isa function of the input voltage and the transformer turnratio. Also, variations in the output load will cause theoutput voltage to change because of circuit parasitics,such as the transformer DC resistance and power switchon resistance. If regulation is necessary, a post regulatorsuch as a linear regulator can be added to the output ofthe supply. See the Typical Applications for examples ofadding a linear regulator.Power ConsiderationThe current derived from the VIN pin and the SWA andSWB switching currents are the sources of the LT3999power dissipation. The power dissipation is the sum of:1) The quiescent current and switch drive powerdissipation:PVIN = VINISW •DC30+4mAwhere ISW is the average switch current.2) Theconductingpowerdissipationoftheswitchesduringon state:PVCESAT = VCESAT • ISW • 2DCwhere DC is the duty cycle and VCESAT is the collectorto emitter voltage drop during the switch saturation.3) The dynamic power dissipation due to the switchingtransitions:PSW = VIN • ISW • fOSC • (tr + tf)where tr and tf are the rise and fall times.The junction temperature is computed as:TJ = TAMB + PD • θJAwhere:PD = PVIN + PVCESAT + PSW and θJA is the packagethermal resistance.Layout Consideration Check ListThe following is a list of recommended layout consider-ations:• Locate the bypass capacitor on the VIN pin of the trans-former close to the transformer.• Create a solid GND plane, preferably on layer two ofthe PCB.• Use short wide traces to connect to the transformer.• The transformer and PCB routing should be care-fully designed to maximize the symmetry between twoswitching half cycles.• SoldertheLT3999exposedpadtothePCB.Addmultiplevias to connect the exposed pad to the GND plane.More HelpAN70: “A Monolithic Switching Regulator with 100mVOutput Noise” contains much information concerningapplications and noise measurement techniques.