📴 iPhone Power Distribution When Turned Off
🔋 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-power circuits |
| PP_BATT_VCC | 4.2V | Battery voltage line |
| PP_CHARGER | 5V | Power input from Lightning cable |
These power rails allow the phone to detect button presses, wake up from alarms, charge, and send signals for Find My iPhone.
🔄 4. Components That Stay Powered
Even when the phone appears off, the following components remain powered in a low-energy state:
🕰️ A. Real-Time Clock (RTC)
- RTC keeps track of time and alarms.
- Stored in a small, low-power memory circuit powered by PP3V0_TRTC.
- Even if the battery is removed, the RTC may still work for a short period using capacitor-stored energy.
📡 B. Find My iPhone / Low-Power Baseband
- iPhones with Find My enabled can still send location updates even when "powered off."
- The Baseband Processor (BB) receives low-power signals from PP1V8_ALWAYS to send a location beacon.
- The Bluetooth & UWB chip (for Find My) stays in a low-energy mode.
🔌 C. Charging Circuit & Lightning Port Detection
- The charging circuit (Tristar/Tigris ICs) remains active to detect power input from a charger.
- If you plug in a Lightning cable, the phone can boot up into the charging screen.
- The PP_CHARGER (5V) line remains active when plugged in.
🖲️ D. Power Button & Wake-Up Logic
- The Power Button Circuit (PP1V8_ALWAYS) remains active to detect when you press the power button.
- When you press the power button, AP_TO_PM_ENABLE signals the PMIC to wake up the CPU.
⚠️ If the iPhone is Completely Dead (No Response to Charging or Power Button)
Possible reasons:
- No VBAT power → Dead battery or disconnected battery.
- PMIC failure → No power regulation to critical components.
- PP1V8_ALWAYS missing → No standby power for essential circuits.
- Damaged power button circuit → Cannot trigger wake-up sequence.
🛠️ Summary: Which Components Have Power When iPhone is Off?
| Component | Powered? | Power Source |
|---|---|---|
| Battery (VBAT) | ✅ Always | VBAT (3.7V-4.2V) |
| PMIC (Power Management IC) | ✅ Always (Low Power Mode) | PP_VDD_MAIN |
| RTC (Real-Time Clock) | ✅ Always | PP3V0_TRTC |
| Baseband Processor (Find My iPhone) | ✅ If enabled | PP1V8_ALWAYS |
| Bluetooth & UWB Chip | ✅ If enabled | PP1V8_ALWAYS |
| Power Button Circuit | ✅ Always | PP1V8_ALWAYS |
| Charging Circuit (Tristar/Tigris) | ✅ Always | PP_CHARGER |
🚀 Final Thoughts
Even when an iPhone is turned off, certain power rails remain active to handle charging, wake-up events, and Find My iPhone functions. The PMIC regulates low-power circuits to keep the device in a ready state.
If an iPhone is completely dead and unresponsive, the issue is likely a power rail failure, PMIC malfunction, or battery disconnection.
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