Datasheet AOZ6763DI (Alpha & Omega) - 10

AOZ6763DI
The peak inductor current is: caused by capacitor value and inductor ripple current. The output ripple voltage calculation can be simplified to: I I L = + ---- Lpeak IO 2  1 V =   ------------- O IL 8  f  CO High inductance gives low inductor ripple current but If the impedance of ESR at switching frequency requires larger size inductor to avoid saturation. Low dominates, the output ripple voltage is mainly decided by ripple current reduces inductor core losses. It also capacitor ESR and inductor ripple current. The output reduces RMS current through inductor and switches, ripple voltage calculation can be further simplified to: which results in less conduction loss. Usually, peak to peak ripple current on inductor is designed to be 20% to 40% of output current. V =   O IL ESRCO 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 inductors are small and radiate less EMI noise. But they IL = ----- cost more than unshielded inductors. The choice ICO_RMS 12 depends on EMI requirement, price and size.
Output Capacitor
Usually, the ripple current rating of the output capacitor is a smaller issue because of the low current stress. When The output capacitor is selected based on the DC output the buck inductor is selected to be very small and voltage rating, output ripple voltage specification and inductor ripple current is high, output capacitor could be ripple current rating. overstressed. The selected output capacitor must have a higher rated
Loop Compensation
voltage specification than the maximum desired output voltage including ripple. De-rating needs to be The AOZ6763DI employs peak current mode control for considered for long term reliability. easy use and fast transient response. Peak current mode control eliminates the double pole effect of the output Output ripple voltage specification is another important L&C filter. It greatly simplifies the compensation loop factor for selecting the output capacitor. In a buck design. converter circuit, output ripple voltage is determined by inductor value, switching frequency, output capacitor With peak current mode control, the buck power stage value and ESR. It can be calculated by the equation can be simplified to be a one-pole and one-zero system below: in frequency domain. The pole is dominant pole can be calculated by:   1 V =  + -------------  O IL ESR  CO 8  f  C  O 1 f  p1  2  C  R where, O L CO is output capacitor value and ESRCO is the The zero is a ESR zero due to output capacitor and its Equivalent Series Resistor of output capacitor. ESR. It is can be calculated by: When a low ESR ceramic capacitor is used as output capacitor, When low ESR ceramic capacitor is used as 1 f  output capacitor, the impedance of the capacitor at the Z 1  2  C  ESR switching frequency dominates. Output ripple is mainly O CO Rev. 1.0 October 2019
www.aosmd.com
Page 10 of 15