📴 iPhone Power Distribution When Turned Off

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🔋 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 RailVoltagePurpose
PP_VDD_MAIN3.7V-4.2VMain power for essential circuits
PP3V0_TRTC3.0VReal-Time Clock (RTC) for system time
PP1V8_ALWAYS1.8VAlways-on low-power circuits
PP_BATT_VCC4.2VBattery voltage line
PP_CHARGER5VPower 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:

  1. No VBAT power → Dead battery or disconnected battery.
  2. PMIC failure → No power regulation to critical components.
  3. PP1V8_ALWAYS missing → No standby power for essential circuits.
  4. Damaged power button circuit → Cannot trigger wake-up sequence.

🛠️ Summary: Which Components Have Power When iPhone is Off?

ComponentPowered?Power Source
Battery (VBAT)✅ AlwaysVBAT (3.7V-4.2V)
PMIC (Power Management IC)✅ Always (Low Power Mode)PP_VDD_MAIN
RTC (Real-Time Clock)✅ AlwaysPP3V0_TRTC
Baseband Processor (Find My iPhone)✅ If enabledPP1V8_ALWAYS
Bluetooth & UWB Chip✅ If enabledPP1V8_ALWAYS
Power Button Circuit✅ AlwaysPP1V8_ALWAYS
Charging Circuit (Tristar/Tigris)✅ AlwaysPP_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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