Why the faulty R7050 caused MacBook battery not charging? – Understand the principles
In order to answer this question, we need to understand the principle of the Apple MacBook charging circuit.
- When a battery is connected to the logic board, a 10KΩ resistor R7050 is connected to the battery connector J7050 pin 15. The smart battery internal circuit detects the presence of the 10KΩ resistor, then opens the battery internal MOSFET to output the battery voltage. In other words, the battery output will remain close unless a 10KΩ resistor is detected. This is the safety feature of the smart battery.
- The battery voltage PPVBAT_G3H_CONN is about 10-12.6V depending on the battery is fully charged or not. PPVBAT_G3H_CONN passes the internal diode of Q7155, charging current sensing resistor R7150, fuse F7140 and becomes PPBUS_G3H power rail.
- Now we have the PPBUS_G3H power rail. Bear in mind that this voltage is passed from the diode inside the MOSFET Q7155. Q7155 is not open yet. So at this moment, this temperate PPBUS_G3H is a “weak” voltage and only can provide very small amount current. But this temperate power rail is powerful enough to power a PMIC to create an always-on power rail PP3V42_G3H.
- The PP3V42_G3H power rail will power up System Management Controller (SMC) and charging PMIC U7100. SMC will read the code stored in the chip inside the battery via a pair of SMBus: SMBUS_BATT_SCL and SMBUS_BATT_SDA. This code contains information such as battery charging status, battery capacity, charging circle counts, temperature and so on.
- If the battery is ok to power the system, SMC will communicate with the charging PMIC U7100 via a pair of SMBUS: SMBUS SMBUS_CHGR_SCL and SMBUS_CHGR_SDA. Then U7100 will output CHGR_BGATE to open MOSFET Q7155. Now we have a stable power PPBUS_G3H power rail ready for use by the laptop.
- When an adaptor is connected to the MacBook, U7100 will create its own version of PPBUS_G3H. U7100 outputs CHGR_BGATE to control the Q7155 to achieve battery charging or discharging. All these functions are governed by the SMC.