Electronic Components Datasheet Search |
|
MIC2199 Datasheet(PDF) 11 Page - Micrel Semiconductor |
|
MIC2199 Datasheet(HTML) 11 Page - Micrel Semiconductor |
11 / 14 page Micrel, Inc. MIC2199. January 2010 11 M9999-011310 Forthelow-sideswitch(N-ChannelMOSFET),theDCpower dissipation is: PR I SWITCH2(dc) DS(on)2 SW 2(rms)2 =× SincetheACswitchinglossesforthelowsideMOSFETis near zero, the total power dissipation is: PP low-sideMOSFET(max) SWITCH2(dc) = ThetotalpowerdissipationforthehighsideMOSFETis: PP P high sideMOSFET(max) SWITCH 1(dc) AC − =+ External Schottky Diode An external freewheeling diode is used to keep the inductor currentflowcontinuouswhilebothMOSFETsareturnedoff. This dead time prevents current from flowing unimpeded through both MOSFETs and is typically 80ns The diode conducts twice during each switching cycle. Although the average current through this diode is small, the diode must be able to handle the peak current. II 2 80ns f D(avg) OUT S =× ×× The reverse voltage requirement of the diode is: VV DIODE(rrm) IN = ThepowerdissipatedbytheSchottkydiodeis: PI V DIODE D(avg) F =× where: VF = forward voltage at the peak diode current TheexternalSchottkydiode,D2,isnotnecessaryforcircuit operationsincethelow-sideMOSFETcontainsaparasitic bodydiode.Theexternaldiodewillimproveefficiencyand decreasehighfrequencynoise.IftheMOSFETbodydiode is used, it must be rated to handle the peak and average cur- rent. The body diode has a relatively slow reverse recovery time and a relatively high forward voltage drop. The power lost in the diode is proportional to the forward voltage drop ofthediode.Asthehigh-sideMOSFETstartstoturnon,the body diode becomes a short circuit for the reverse recovery period, dissipating additional power. The diode recovery and the circuit inductance will cause ringing during the high-side MOSFETturn-on. AnexternalSchottkydiodeconductsatalowerforwardvoltage preventingthebodydiodeintheMOSFETfromturningon. The lower forward voltage drop dissipates less power than the body diode. The lack of a reverse recovery mechanism inaSchottkydiodecauseslessringingandlesspowerloss. Depending on the circuit components and operating condi- tions, an external Schottky diode will give a 1/2% to 1% improvementinefficiency. Output Capacitor Selection The output capacitor values are usually determined by the capacitorsESR(equivalentseriesresistance).Voltagerating andRMScurrentcapabilityaretwootherimportantfactorsin selecting the output capacitor. Recommended capacitors are tantalum,low-ESRaluminumelectrolytics,andOS-CON. Theoutputcapacitor’sESRisusuallythemaincauseofoutput ripple.ThemaximumvalueofESRiscalculatedby: R V I ESR OUT PP ≤ ∆ where: VOUT = peak-to-peak output voltage ripple IPP = peak-to-peak inductor ripple current ThetotaloutputrippleisacombinationoftheESRandthe output capacitance. The total ripple is calculated below: ∆V I(1D) Cf IR OUT PP OUT S 2 PP ESR 2 = ×− × +× () where: D = duty cycle COUT = output capacitance value fS = switching frequency The voltage rating of capacitor should be twice the output voltage for a tantalum and 20% greater for an aluminum electrolyticorOS-CON. TheoutputcapacitorRMScurrentiscalculatedbelow: I I 12 C PP OUT(rms) = The power dissipated in the output capacitor is: PI R DISS(C C ESR(C ) OUT OUT(rms)2 OUT ) =× Input Capacitor Selection The input capacitor should be selected for ripple current rating and voltage rating. Tantalum input capacitors may fail when subjected to high inrush currents, caused by turning the input supply on. Tantalum input capacitor voltage rating should be at least 2 times the maximum input voltage to maximize reliability. Aluminum electrolytic, OS-CON, and multilayer polymerfilmcapacitorscanhandlethehigherinrushcurrents without voltage derating. The input voltage ripple will primarily depend on the input capacitorsESR.Thepeakinputcurrentisequaltothepeak inductor current, so: ∆VI R IN INDUCTOR(peak) ESR(C ) IN =× The input capacitor must be rated for the input current ripple. TheRMSvalueofinputcapacitorcurrentisdeterminedat the maximum output current. Assuming the peak-to-peak inductor ripple current is low: II D(1D) C (rms) OUT(max) IN ≈× ×− The power dissipated in the input capacitor is: PI R DISS(C ) C (rms) ESR(C ) IN IN 2 IN =× |
Similar Part No. - MIC2199_10 |
|
Similar Description - MIC2199_10 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |