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AAT1217 Datasheet(PDF) 9 Page - Advanced Analogic Technologies |
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AAT1217 Datasheet(HTML) 9 Page - Advanced Analogic Technologies |
9 / 13 page IPEAK Peak Inductor Current IDC DC Component (Average) of the Inductor Current ∆IL Peak-Peak Inductor Ripple Current IOUT Output (Load) Current VOUT Output Voltage VIN Input Voltage η AAT1217 Efficiency (consult the perform- ance graphs in the “Typical Characteristics” section of the data sheet) D Steady-State Duty Cycle FSW Switching Frequency L Inductor Value For a given chosen inductor value and application conditionsmakesurethepeakinductorcurrentdoes notexceedthemaximumcurrentratingoftheselect- edvendor’sinductor. Foroptimumloadtransientand efficiency, low DCR inductors should be selected. Table 2 lists some typical surface mount inductors that aresuitable fortypicalAAT1217applications. Input Capacitor A surface mount 4.7µF or greater, X5R or X7R, ceramiccapacitorissuggestedfortheinputcapac- itor. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT1217. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize stray inductance, the capacitor should be placed as close as possible to the IC. This keeps the high frequency content of the input current localized, minimizing EMI and input voltage ripple. Always examine the ceramic capacitor DC voltage coeffi- cient characteristics to get the proper value. For example, the capacitance of a 10µF, 6.3V, X5R ceramic capacitor with 5.0V DC applied is actually about 6µF. Alaboratorytestset-uptypicallyconsistsoftwolong wires running from the bench power supply to the evaluation board input voltage pins.The inductance ofthesewires,alongwiththelow-ESRceramicinput capacitor, can create a high Q network that may affect converter performance. This problem often becomes apparent in the form of excessive ringing in the output voltage during load transients which can produce errors in loop phase and gain meas- urements. Since the inductance of a short printed circuitboard(PCB)tracefeedingtheinputvoltageis significantly lower than the power leads from the benchpowersupply,mostactualapplicationsdonot exhibitthisproblem. Inapplicationswheretheinput powersourceleadinductancecannotbereducedto a level that does not affect the converter perform- ance, a high ESR tantalum or aluminum electrolytic capacitor should be placed in parallel with the low ESR,ESLbypassinputceramiccapacitor.Theintro- ductionofthehighESRcapacitordampensthehigh Q network and stabilizes theAAT1217. I PEAK = + I OUT · V OUT η · V IN V IN · (V OUT - V IN ) 2L · F SW · V OUT ∆ IL = ; D = = VIN · (VOUT - VIN) L · FSW · VOUT VIN · D L · FSW VOUT - VIN VOUT ∆ IL I DC = I OUT · V OUT η · V IN I PEAK = I DC + ∆I L 2 AAT1217 600mA, 1.2MHz, Micropower Synchronous Step-Up Converter 1217.2007.07.1.0 9 |
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Similar Description - AAT1217 |
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