What does Q1403 do?

okay I got a 6 that had water damage, removed shorted caps etc. Board looks very good, but it is missing Q1403. When plugged in, the cpu heats up a bit but that's it. I was thinking q1403 reported the battery voltage, and if its not there it would probably show 0% but I could be totally wrong. Could I get this board to fire up without it? I tried to source this ic from another board but I was taking it off a board and then dropped the ic on a carpet floor, then I ran out of donor boards. anywahy, what does it do and can it work without it?

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As @oldturkey03 says, Q1403 is a power MOSFET (P-Channel enhancement mode MOSFET). This kind of FET is used for high-side switching, allowing PP_VCC_MAIN to charge the battery or not.

So in essence:

  • PP5V0_USB gets converted to ~4.25V by the internal Buck converter in Tigris to create PP_VCC_MAIN.
  • CHG_ACT_DIO will go low (0V) when it detects something in the charge port.
  • VCC_MAIN & BATT_VCC are connected together via Q1403 and battery charging occurs.
  • When the battery is fully charged, CHG_ACT_DIO goes high and cuts the connection between PP_VCC_MAIN & PP_BATT_VCC.

What's not entirely clear is what the battery lines in Tigris (A1-D1) do because we don't know what the internal logic is. Are they switched internally to output at VDD_MAIN (A2-D2) when no charging occurs or does BATT_VCC go though the body diode of the MOSFET to supply VCC_MAIN? Given that there is very little Forward Voltage drop measured across the body diode, I believe it is the former and not the latter. Only the Apple engineers know for sure.

EDIT

I've edited this answer so that it is a little clearer and more importantly, there is a big unknown because no one knows what the internal logic of TIGRIS is. This answer is my "reading" of the schematic. Only the Apple engineers know for certain what goes on inside TIGRIS.

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The phone won't charge but will it still turn on?

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Haven't tried it myself but I guess it should. It will require to have a charger plugged in to supply VCC_MAIN.

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my batt_vcc is oscilating between 2v14 to 4v14 m that could be a faulty q1403?

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At the moment battery is full .. the mosfet cut off vcc main with batt vcc .. and tigris makes connectting between 5V0 usb with vcc main ..

The diode inside mosfet didnt go forward because batt vcc and vcc main carry same voltage approximately..

when charger cable disconnect .. tigris makes connectting between batt vcc and vcc main ..

Sorry for bad my English

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Q1403 is a CSD68815W15 Q4 power MOSFET for the power/battery circuitry. Here is the datasheet P-Channel NexFET Power MOSFET, CSD22202W15 Does not look like that you can bypass it. I suggest that you replace it cost is around $10 for 3. It is a BGA IC and therefore will require some good/different soldering techniques. If you do not have the tools for this job, consider sending it someone that does boardlevel repair.

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I can do bga soldering, I'm just not very good at it. This board is my little project :)

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@gigabit87898 did not mean to imply that you can't :-)

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For diagnostic purposes or a fun hobby project on your own phone—just lay a wire connecting vccmain to battvcc at the pads that q1403 used to sit on. This will let you continue diagnosing and the phone will boot this way if there are no other problems. Since a phone can not boot without a battery connected at all (i.e. a phone can not boot from just usb5v) then I would guess that there is a chance that the phone can not boot without the mosfet at all (although maybe it can, i’ve always just jumped it and never tried without) as long as the phone is getting battery data through tigris.

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Jesse, please is the vdd_main indicated on the tigris chip , a power line to power the tigris chip in other to work or a power line from the tigris chip to soc , cpu ,sdram as its indicated vdd main. Is it, input supply voltage to TIGRIS or output supply voltage from the TIGRIS chip and well, if it does an output job, does it go to the trister and to pmu as vcc_main and be converted from the pmu as a vdd _main to the soc, cpu, sdram. Please help, am just a beginner from Ghana west africa

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