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iPhone starts with high current

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In this video we mainly explain

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Advanced Power-on High Current Principle 2 Verification of Working Principle

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According to the video content explained in the previous section

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After the BUCK conversion module generates power

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will be LDO

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And BUCK_SWITCHES module to provide working voltage

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These modules then generate some power

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that in our actual maintenance

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May experience a malfunction

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When the LDO power supply of BUCK power supply conversion is short-circuited

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Or when the converted BUCK_SWITCHES power supply is short-circuited

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Our switching inductors get hot

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But when we use a multimeter to measure the secondary body value

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His numbers are still normal

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In this case the conversion

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LDO power supply or BUCK_SWITCHES power supply is caused by a short circuit

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Next let's verify

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We use the iPhone8P model to find drawings and do experiments

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Because the iPhone 8P model is a long strip motherboard

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It is more convenient when doing experiments

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If it is a double-layer motherboard

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It is troublesome to need layered fit

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We find the main power in the callout group

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Go to the drawings to search for the main power supply

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we use the power

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BUCK3 power supply as an example to demonstrate

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BUCK3 power supply

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through the inductor L2730 will generate

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PP1V8_S2 power supply

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PP1V8_S2 power supply will return to the inside of the chip

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Used to convert BUCK3_SW1, 2, 3

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then we will

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The power supply capacitor of BUCK3_SW3

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Let's take a look after C3622 is shorted

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inductance

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L2730

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Will it be hot?

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After we short circuit C3622

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Rosin on Inductor L2730

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Let's turn it on again and see if the rosin melts

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After C3622 is shorted, we trigger the switch

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At this time we can see the current

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Directly around 700mA

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At this time we are

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See if the rosin melts

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After triggering the switch

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The rosin on the inductor melts slowly

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after a while

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We can see that

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The rosin on the inductor has melted

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Let's measure again next time

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The ground value of this power supply

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We will find that the diode value is still normal

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Let's verify it next

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BUCK power supply to LDO power supply

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After the LDO power supply is short-circuited, it will also cause

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Inductor generating current heats up

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Let's take BUCK4, PP1V1_S2 power supply as an example

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Then this power supply will return to the inside of the chip

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Used to transfer LDO4

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LDO8 and LDO14

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Then we will supply power to LDO8

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0.9V HDD power supply

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The capacitor above the supply line

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C2602 short circuit

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Let's take a look later

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BUCK4

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Power supply inductance

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Does the L2741 get hot?

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Below we short the capacitor C2602

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Then smoke the inductor L2741 with rosin

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We're triggering the boot to see if the rosin melts

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After power on, the current becomes 500mA

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Below we are under the microscope

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Will the inductor melt?

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Inductor L2741

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Found that the rosin on the top is slowly melting

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wait about 1 minute

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we will find

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The rosin on the inductor has melted

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after power outage

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below

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We use a multimeter to measure the resistance of the power supply

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At this time we found

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The value of the power supply is around 50

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At this time, the board is a little hot

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So the value is low

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When we repair

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this may happen

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Inductor is hot

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But when we measure the secondary body value, the value is normal

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At this time we have to think

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It may be that the inductance is hot caused by the conversion circuit of the rear pole

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During our actual maintenance

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There may also be a glitch

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It is the high current at startup

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but we measure

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When all BUCK power supply and LDO power supply

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he didn't short circuit

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But the current is very large after starting up

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like this situation

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possible

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It is caused by the empty welding of the inductor powered by BUCK

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Because the mobile phone motherboard is relatively small

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His switching MOS tube

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are integrated inside the power IC

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Then the inductor is externally

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Then if the inductor is air-welded

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It will cause the internal switch tube to work abnormally.

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resulting in high current

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Power-on high current fault

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all the course content

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we're done talking here