SLUSCQ8A May 2017 – May 2018
PRODUCTION DATA.
Output capacitor also should have enough ripple current rating to absorb output switching ripple current. In buck mode the output capacitor RMS current is given:
To get good loop stability, the resonant frequency of the output inductor and output capacitor should be designed between 10 kHz and 20 kHz. The preferred ceramic capacitor is 25-V X7R or X5R for output capacitor. Minimum 6 pcs of 10-µF 0805 size capacitor is suggested to be placed by the inductor. Place the capacitors after Q4 drain. Place minimum 10 µF after the charge current sense resistor for best stability.
Ceramic capacitors show a dc-bias effect. This effect reduces the effective capacitance when a dc-bias voltage is applied across a ceramic capacitor, as on the output capacitor of a charger. The effect may lead to a significant capacitance drop, especially for high output voltages and small capacitor packages. See the manufacturer's data sheet about the performance with a dc bias voltage applied. It may be necessary to choose a higher voltage rating or nominal capacitance value in order to get the required value at the operating point.