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High current when iPhone starts up

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In this lesson, we mainly explain the advanced principle of high current on the boot

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From the previous course,

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we know that the power supply IC is mainly to convert the power supply of the battery

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into the voltage required by each chip

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When the power IC is converting the power supply,

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it has two modes,

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one is BUCK mode and the other is LDO mode

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There are many connections between them

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Let's look at it in detail

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In the first step, when we plug in the battery or switch on the adjustable power supply,

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the main power supply will receive the PP_VDD_MAIN power supply

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This main power supply will feed into a number of pins of the power supply IC,

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which will provide the operating voltage for the conversion of the BUCK power supply later

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When we press the switch,

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the switch signal is sent to the main power supply,

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which turns on the conversion module

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Different modules generate different power supplies

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The power supply of BUCK generates a large current through the inductor

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The more inductor, the greater the current it generates

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For example, some power supplies will have one inductor,

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some will have two or even three, and some will have four inductors

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When the BUCK power supply is generated,

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in addition to providing operating voltage to the chip,

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it will return to the chip and provide operating voltage to either the LDO module inside the chip

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or the BUCK SWITCHES module inside the chip

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After these modules have power supply,

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they will convert the LDO power supply without inductor,

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and then convert it to power supply,

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and its current will be relatively small

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Let's use the iPhone 8P model as an example to find drawings and experiment

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Because the iPhone 8P model is a long strip mainboard,

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it is easier to do experiments

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If it is a double-layer mainboard, we need to layer and fit, very troublesome

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We find the main power supply in the component map,

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and search it in the circuit diagram

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After finding the power supply,

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let's first look at each power supply module of PP_VDD_MAIN main supply

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In the circuit diagram, many names will be marked after the main power supply enters the power IC

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Different names represent different power supplies

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For example, the main power supply comes and goes into the pins

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M15, 16, 17, 18 of the power supply IC

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These pins are designed to power routes 0 and 1 of BUCK0

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T15, T16, T17, T18,

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these pins are mainly powered for the second and third circuits that convert BUCK0 power supply

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Let's take a look at the power supply of BUCK0

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BUCK0 power supply consists of four inductors,

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and its power supply will be marked

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For example, the first one,

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LX0 refers to the 0 power supply of BUCK0

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We have route 1 of BUCK0, route 2 of BUCK0, route 3 of BUCK0

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Different pins are used specifically to convert different power supplies

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For example, Y15, Y16 and Y17,

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they are mainly used to convert the power supply of BUCK7

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This power supply refers to the BUCK7 power supply,

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which is generated by an inductor

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So it has less power supply input pins

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Now let's look at the conversion mode of LDO power supply

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In this power supply module, the left side belongs to LDO input,

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and the right side belongs to LDO output

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LDO input, we can see that after the power supply comes in,

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it will connect different power supply names

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Like the position on the left,

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PP1V1_S2 is powered by PP1V25_S2

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When the power came in, they switched to a different power supply

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PP1V1 is used to convert power supply to LDO4, LDO8 and LDO14

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Now let's look at the power supply of LDO4

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The power supply of LDO4 is 0.7V,

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which is changed from 1.1 to 0.7V

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The power supply of LDO 8 is 0.9V,

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which is changed from 1.1 to 0.9V

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This is a conversion of the LDO power supply

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When the power supply is converted,

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it is converted to a similar power supply

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The power supply advantage of this conversion is a small voltage drop,

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which means less battery loss

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That way, the battery will last longer

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Let's take a look at the SWITCH OUTPUTS power supply conversion module

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In the circuit diagram, BUCK3 passes through an inductor

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After generating PP1V8_S2 power supply,

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we can see that there is a line, back inside the power IC

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This power supply will convert SWITCH OUTPUTS power supply

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This power supply will be converted into BUCK3_SW1,

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BUCK3_SW2, BUCK3_SW3

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All three are 1.8V

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Ok, that's it for this lesson