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L3380-27-AF5-R Datasheet(PDF) 7 Page - Unisonic Technologies |
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L3380-27-AF5-R Datasheet(HTML) 7 Page - Unisonic Technologies |
7 / 9 page L3380 CMOS IC UNISONICTECHNOLOGIESCO.,LTD 7 of 9 www.unisonic.com.tw QW-R502-099,A APPLICATION CIRCUIT INFORMATION (Cont.) 5. Charge stores in C3 during charging up is given by COFF QI T ∆ =• we can write 1 () LO d QI I f − ∆= − • 6. Output ripple voltage is given by () PPC L O VU ESR I I =∆ + • − (ESR: equivalent series resistance of the output capacitor) () PPL O Q VESR I I C ∆ =+ • − Then we give the following example about choosing external components by considering the design parameters. Design parameters: IN U =1.5V Uo =2.1V O I =200mA PP V =100mV f=300KHZ ICR=0.2 Assume D U and S U are both 0.3V, the duty ratio is 2.1 0.3 1.5 0.429 2.1 0.3 0.3 OD IN OD S UU U d UU U +− +− == = +− + − In order to generate the desired output current and ICR, the value of inductor should meets the following formula L ≤ (1– d) 2(U O+UD-UIN) ICR • IO • f = (1– 0.429) 2(2.1V+0.3V-1.5V) 0.2×0.2A×300000HZ = 24.5uH Calculate the average current and the peak current of inductor 0.2 0.35 1 1 0.429 O L I A I A d == = −− 11 (1 ) 0.35 (1 0.2) 0.385 22 PK L I IICR A A =+ = × + × = So, we make a trial of choosing a 22uH inductor that allowable maximum current is lager than 0.385A. Determine the delta charge stores in C3 during charging up 1 1 0.429 ( ) (0.35 0.2 ) 0.286 300000 LO d QI I A A uC fHZ −− ∆= − • = − × = Assume the ESR of C3 is 0.15Ω, determine the value of C3 6 0.286 10 3.69 ( ) 0.1 0.15 (0.35 0.2 ) PP L O QC CuF VESR I I A A − ∆× ≥= = −• − − Ω× − Therefore, a Tantalum capacitor with value of 10uF and ESR of 0.15Ω can be used as output capacitor. However, the optimized value should be obtained by experiment. |
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