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ACT4529M データシート(PDF) 8 Page - Active-Semi, Inc |
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ACT4529M データシート(HTML) 8 Page - Active-Semi, Inc |
8 / 15 page ACT4529M Rev 1, 23-Feb-17 Innovative PowerTM - 8 - www.active-semi.com Copyright © 2016-2017 Active-Semi, Inc. APPLICATIONS INFORMATION Inductor Selection The inductor maintains a continuous current to the output load. This inductor current has a ripple that is dependent on the inductance value. Higher inductance reduces the peak-to-peak ripple current. The trade off for high inductance value is the increase in inductor core size and series resistance, and the reduction in current handling capability. In general, select an inductance value L based on ripple current requirement: Where VIN is the input voltage, VOUT is the output voltage, fSW is the switching frequency, ILOADMAX is the maximum load current, and KRIPPLE is the ripple factor. Typically, choose KRIPPLE = 30% to correspond to the peak-to-peak ripple current being 30% of the maximum load current. With a selected inductor value the peak-to-peak inductor current is estimated as: The peak inductor current is estimated as: The selected inductor should not saturate at ILPK. The maximum output current is calculated as: LLIM is the internal current limit. Input Capacitor The input capacitor needs to be carefully selected to maintain sufficiently low ripple at the supply input of the converter. A low ESR capacitor is highly recommended. Since large current flows in and out of this capacitor during switching, its ESR also affects efficiency. The input capacitance needs to be higher than 10µF. The best choice is the ceramic type. However, low ESR tantalum or electrolytic types may also be used provided that the RMS ripple current rating is higher than 50% of the output current. The input capacitor should be placed close to the IN and GND pins of the IC, with the shortest traces possible. In the case of tantalum or electrolytic types, a ceramic capacitor is recommended to parallel with tantalum or electrolytic capacitor, which should be placed right next to the IC. Output Capacitor The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is: Where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is the ESR of the output capacitor, fSW is the switching frequency, L is the inductor value, and COUT is the output capacitance. From the equation above, VRIPPLE is the combination of ESR and real capacitance. In the case of ceramic output capacitors, RESR is very small and does not contribute to the ripple. Therefore, a lower capacitance value can be used for ceramic type. In the case of tantalum or electrolytic capacitors, the ripple is dominated by RESR multiplied by the ripple current. In that case, the output capacitor is chosen to have sufficiently low ESR. For ceramic output capacitor, typically choose a capacitance of about 22µF. For tantalum or electrolytic capacitors, choose a capacitor with less than 50mΩ ESR. When 330uF or 470uF electrolytic cap or tantalum cap is used, where ripple is dominantly caused by ESR, a 2.2uF ceramic in parallel is recommended. Rectifier Schottky Diode Use a Schottky diode as the rectifier to conduct current when the High-Side Power Switch is off. The Schottky diode must have current rating higher than the maximum output current and a reverse voltage rating higher than the maximum input voltage. Further more, the low forward voltage Schottky is preferable for high efficiency and smoothly operation. (1) (2) (3) (4) (5) |
同様の部品番号 - ACT4529M |
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同様の説明 - ACT4529M |
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