Power Rails from Battery Connector to Charging IC
PP_BATT_VCC : This is the main battery voltage rail that originates directly from the battery connector. It carries the raw battery voltage (typically 3.8V–4.2V, depending on charge level) into the mainboard. It’s the starting point of power distribution and feeds into various subsystems, including the charging and power management circuits. PP_VCC_MAIN : After PP_BATT_VCC, the voltage often passes through protective components (like fuses or MOSFETs) and becomes PP_VCC_MAIN. This rail powers the primary circuits on the board, including the Power Management IC (PMIC) and, indirectly, the charging IC. On the iPhone 12 Pro, this rail is a key intermediary between the battery and downstream power regulation. PP_BUS (or similar intermediate rail)**: Some iPhone designs use an intermediate bus voltage rail (sometimes labeled PP_BUS or a variant) that connects PP_BATT_VCC to the charging IC and other components. This rail might be filtered or regulated slightly before reach...