The fast growing market of charging case brings big opportunities as well as challenges for the power design. The limited product size drives the power efficiency to be very critical. The huge volumes also drives the market to be cost-sensitive. A good trade off should be made between the solution cost and performance. In this ultra-low standby power reference design, a charger gets power from the USB input and charges the charging case battery (BAT1) as shown in Figure 1 block diagram . This charger supplies the boost converter as well.