Released on September 19, 2014, this 4.7" screen iPhone is the smaller version of the iPhone 6 Plus.

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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, it is a power 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. However, due to the Body Diode in the FET, BATT_VCC can still supply current to PP_VCC_MAIN and hence the rest of the device.

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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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Most Helpful Answer

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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