Datasheet AOZ6682CI (Alpha & Omega) - 10

AOZ6682CI
When selecting the inductor, make sure it is able to For lower output ripple voltage across the entire handle the peak current without saturation even at the operating temperature range, X5R or X7R dielectric type highest operating temperature. of ceramic, or other low ESR tantalum are recommended to be used as output capacitors. The inductor takes the highest current in a buck circuit. The conduction loss on inductor need to be checked for In a buck converter, output capacitor current is thermal and efficiency requirements. continuous. The RMS current of output capacitor is decided by the peak to peak inductor ripple current. It can Surface mount inductors in different shape and styles are be calculated by: available from Coilcraft, Elytone and Murata. Shielded I inductors are small and radiate less EMI noise. But they I L = ----- cost more than unshielded inductors. The choice CO_RMS 12 depends on EMI requirement, price and size. Usually, the ripple current rating of the output capacitor is For the current mode control, the minimum inductor a smaller issue because of the low current stress. When 2.2uH is recommended to prevent the current running the buck inductor is selected to be very small and away in the extreme case. inductor ripple current is high, output capacitor could be
Output Capacitor
overstressed. The output capacitor is selected based on the DC output voltage rating, output ripple voltage specification and ripple current rating. The capacitor must have a higher rated voltage specification than the maximum desired output voltage including ripple. De-rating needs to be considered for long term reliability. Output ripple voltage specification is another important factor for selecting the output capacitor. In a buck converter circuit, output ripple voltage is determined by inductor value, switching frequency, output capacitor value and ESR. It can be calculated by the equation below:   1 V =  + -------------  O IL ESR  CO 8  f  C  O where CO is output capacitor value and ESRCO is the Equivalent Series Resistor of output capacitor. When low ESR ceramic capacitor is used as output capacitor, the impedance of the capacitor at the switching frequency dominates. Output ripple is mainly caused by capacitor value and inductor ripple current. The output ripple voltage calculation can be simplified to:  1 V =   ------------- O IL 8  f  CO If the impedance of ESR at switching frequency dominates, the output ripple voltage is mainly decided by capacitor ESR and inductor ripple current. The output ripple voltage calculation can be further simplified to: V =   O IL ESRCO Rev. 1.0 December 2018
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