High current when iPhone starts up

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

From the previous course,

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

into the voltage required by each chip

When the power IC is converting the power supply,

it has two modes,

one is BUCK mode and the other is LDO mode

There are many connections between them

Let's look at it in detail

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

the main power supply will receive the PP_VDD_MAIN power supply

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

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

When we press the switch,

the switch signal is sent to the main power supply,

which turns on the conversion module

Different modules generate different power supplies

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

The more inductor, the greater the current it generates

For example, some power supplies will have one inductor,

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

When the BUCK power supply is generated,

in addition to providing operating voltage to the chip,

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

or the BUCK SWITCHES module inside the chip

After these modules have power supply,

they will convert the LDO power supply without inductor,

and then convert it to power supply,

and its current will be relatively small

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

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

it is easier to do experiments

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

We find the main power supply in the component map,

and search it in the circuit diagram

After finding the power supply,

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

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

Different names represent different power supplies

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

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

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

T15, T16, T17, T18,

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

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

BUCK0 power supply consists of four inductors,

and its power supply will be marked

For example, the first one,

LX0 refers to the 0 power supply of BUCK0

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

Different pins are used specifically to convert different power supplies

For example, Y15, Y16 and Y17,

they are mainly used to convert the power supply of BUCK7

This power supply refers to the BUCK7 power supply,

which is generated by an inductor

So it has less power supply input pins

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

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

and the right side belongs to LDO output

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

it will connect different power supply names

Like the position on the left,

PP1V1_S2 is powered by PP1V25_S2

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

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

Now let's look at the power supply of LDO4

The power supply of LDO4 is 0.7V,

which is changed from 1.1 to 0.7V

The power supply of LDO 8 is 0.9V,

which is changed from 1.1 to 0.9V

This is a conversion of the LDO power supply

When the power supply is converted,

it is converted to a similar power supply

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

which means less battery loss

That way, the battery will last longer

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

In the circuit diagram, BUCK3 passes through an inductor

After generating PP1V8_S2 power supply,

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

This power supply will convert SWITCH OUTPUTS power supply

This power supply will be converted into BUCK3_SW1,

BUCK3_SW2, BUCK3_SW3

All three are 1.8V

Ok, that's it for this lesson