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Small current when iPhone is turned on

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In this lesson, we mainly learn the working principle of the small current circuit when starting up

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The working principle of small current is suitable for all Apple models

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Let's take a look at the workflow of small current

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First step, when we buckle the battery or connect the adjustable power supply,

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the main power supply will be generated

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In the second step, after the main power supply receives the main power supply,

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it will generate PP1V8_ALWAYS standby power supply

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In the third step, after the power supply generates standby power,

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it will be connected through the circuit inside the chip

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to provide a pull-up voltage for the switch pin

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The fourth step, when we short the switch pin,

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the switch pin voltage will change from 1.8V to 0V

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This signal will be sent to the main power supply

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After the main power supply receives the power-on signal,

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it will generate more than 30 power supplies,

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which will provide working voltage for the chip on the mainboard

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With so many chips on the mainboard, the CPU will work first,

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and the chip needs power supply, clock signal and reset signal to work

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After booting, the CPU has power supply

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After the CPU has power supply, the clock module inside the CPU starts to work,

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providing a working voltage for the 24M crystal oscillator

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After the crystal oscillator is powered,

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it will generate a 24M clock signal

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and return it to the CPU to provide a reference clock for the clock module inside the CPU

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This clock will provide a clock signal for future working circuits

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When the clock module works normally,

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it will send a test clock to the main power supply, TEST_CLKOUT

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After the main power supply receives the test clock,

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it will send a reset signal to the CPU

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After the CPU has power supply, clock signal and reset signal,

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its internal integrated startup module will work

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After the startup module works, it will consume power,

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and the current will be displayed on the adjustable power supply

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Small current means that the startup module does not work at all,

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So we see that the current on the adjustable power supply is very small

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If the startup module wants to work,

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it needs power supply, clock signal and reset signal

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If one of these three conditions is abnormal,

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it will cause a small current fault

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When we overhaul, we need to overhaul the CPU's power supply, clock signal and reset signal

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That's all for this video