A Classic Blog

  🔋 1. Battery (VBAT) Supplies Standby Power The VBAT (Main Battery Line) is always connected to the logic board, even when the iPhone is off. VBAT voltage: ~3.7V-4.2V , depending on battery charge. ⚠️ If VBAT is missing or disconnected, the iPhone will not turn on, even when plugged into a charger. ⚡ 2. Power Management IC (PMIC) is Always Active PMIC (Power Management Integrated Circuit) remains partially active to manage charging, power button detection, and wake-up events. PMIC generates low-power standby voltages to supply essential circuits. These voltages keep the iPhone "ready to turn on" when needed. ⚠️ If PMIC fails, the iPhone will be completely dead (no charging, no response). 📶 3. Always-On Power Rails (Even When Off) Some power rails remain active even when the phone is off, including: Power Rail Voltage Purpose PP_VDD_MAIN 3.7V-4.2V Main power for essential circuits PP3V0_TRTC 3.0V Real-Time Clock (RTC) for system time PP1V8_ALWAYS 1.8V Always-on low-powe...

  🔋 1. Power Source & Initial Activation This stage involves powering the device and initializing voltage regulators . Step 1: Battery or Charger Supplies Power The iPhone receives power from either: The battery (connected via VBAT) The Lightning port (if charging or connected to a computer) VBAT Line (Main Battery Line) VBAT is the main power rail connected directly to the battery. It supplies raw battery voltage (3.7V - 4.35V) to the Power Management IC (PMIC) . If VBAT is missing or disrupted, the phone will not power on . ⚡ 2. Power Management & Voltage Regulation Step 2: Power Management IC (PMIC) Activation The PMIC (Power Management Integrated Circuit) is responsible for regulating voltage and distributing power to various components. The PMIC is controlled by the AP_TO_PM_ENABLE signal , which is triggered when the power button is pressed. Step 3: PMIC Generates Power Rails The PMIC takes the raw VBAT voltage and converts it into different power rails: Power...

  🔹 Stage 1: Power-On & Hardware Initialization This stage handles the basic power flow and hardware activation. 1️⃣ Power Button Pressed Pressing the power button signals the PMU (Power Management Unit) to begin powering up the device. PMU activates components like: CPU (Processor) RAM (Random Access Memory) NAND Storage (Flash Memory) Baseband Processor (For Cellular Communication) Battery Management System 🔹 Stage 2: BootROM Execution (First Bootloader - Immutable Code) Now that the device has power, the processor executes BootROM , the first-stage bootloader stored in read-only memory (ROM) inside the CPU. 2️⃣ BootROM Execution BootROM is the first line of defense in iOS security and cannot be modified. It performs an Initial Integrity Check to verify if the firmware is valid. It loads the Apple Secure Boot Chain , a multi-step process ensuring only Apple-approved software is used. 🔹 Stage 3: Secure Boot Chain & Low-Level Bootloading BootROM now begins executin...