SLUSDV2A May 2020 – May 2021 BQ25798
In the boost mode operation, the output current is discontinuous, which dominates the output RMS ripple current and output voltage ripple. The output capacitors should have enough ripple current rating to absorb the output AC current and have large enough capacitance to maintain the small output voltage ripple. For the boost mode operation, the output RMS ripple current is calculated by the equation (8) and the output voltage ripple is calculated by the equation (9), where D = (1 - VBUS / VSYS).
The worst case output RMS ripple current and output voltage ripple both occur at the lowest VBUS input voltage. The SYS voltage is approximately 8V for the 2s battery configuration, so the worst case is 5V VBUS condition. Low ESR ceramic capacitor such as X7R or X5R is preferred for the output decoupling capacitor and should be placed close to the SYS and GND pins of the IC. The voltage rating of the capacitor must be higher than the normal input voltage level. The capacitor with 16V or higher voltage rating is preferred for the 2s battery configuration. 1*0.1 μF + 5*10 μF capacitors are suggested for up to 5A charging current.