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I want to use STUSB4500 in a project, to have USB C PD. A MCU will also be on the same PCB and it will control the STUSB4500 via I2C.

There are two schematics in the datasheet (https://www.st.com/resource/en/datasheet/stusb4500.pdf) on page 24 and 25. One is for standalone use, one for use with a MCU. The MCU version has an additional MOSFET in the power path (T4), and I do not really understand why it's in there. Can I leave it out in my design, to save on BOM and board space? On the evaluation board, T4 can also be bridged by a 0R resistor...

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  • \$\begingroup\$ The second MOSFET allows disconnecting power in both directions, e.g. both into the USB socket and out from it. If this project can both be powered from USB and power something else via USB, you need both. \$\endgroup\$
    – user16324
    Commented Mar 27, 2020 at 17:30
  • \$\begingroup\$ Thank you, I also assumed that this was the reason for the second MOSFET. I was just wondering because this was mentioned nowhere in the datasheet, and this IC is specifically only for power in one direction... \$\endgroup\$
    – Spatz
    Commented Mar 27, 2020 at 20:18

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MOSFET T4 is to ensure the cold socket, preventing incoming negative voltage on VBUS. Removing T4 can save the cost and PCB space, but it will not be protected for negative voltage nor reverse battery - the reverse current flowing from the battery charger to the Source.

To remove it or to keep it depends on the application needs for the protection.

MOSFET T1 acts as a ON-OFF switch, to guarantee no load when the device is not attached to a Source. Consider it as something must. Removing T1 may have a drawback not compliant to the standard.

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