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I'm trying to use a low-side MOSFET to disable/enable a few sensor module boards (MS5611 pressure sensor, MPU9250 IMU and a GPS/BDS module) connected to an ESP32 (which runs off 3.3V rails). These sensor module boards work with 3.3V supply, and probably consume between 50-150mA current (not measured, but a guess, and is probably on the higher side than actual consumption).

To perform a hardware reset and save power when not in use, I'm looking to turn off these modules using a low-side MOSFET AO3402 (primarily because this is available at local stores, and is cheap).

I'd like to understand if AO3402 is a good part number to use for the schematic below? An alternative part number available easily is Si2302DS. Is there a design that is better than the one here?

Thanks!

Schematic

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    \$\begingroup\$ Low side mosfet is problematic. When OFF, GND becomes 3.3V meaning various I/O signals are below GND. It's even possible the circuit remains powered by those I/O signals via their protection diodes (designed to prevent damage by inputs below 0V). Satisfy yourself that each and every I/O signal will be 3.3V before switching off. (This same Q came up about a week ago : search for answers to it!) \$\endgroup\$
    – user16324
    Aug 5, 2021 at 16:29
  • \$\begingroup\$ Are you sure that some of peripherals can't be driven directly (as supply) by GPIO pins ? (ATGM336H not, ok, 100mA minimum) (MS5611 1.4mA ok) (MPU9250 3.2mA+ 450uA + 280 UA +... = 3.9 mA ok) \$\endgroup\$
    – Antonio51
    Aug 5, 2021 at 17:51

2 Answers 2

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You should breadboard this first to see if it really works. If you have disconnected ground from some devices but still have some of their inputs connected to the ESP32 then you may draw current through the input protection diodes of your peripheral devices. You may need to force SCL, SDA, and TX high when ground is removed from these devices.

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I know you selected the AO3402 due to availability, but it might be easier to just consider using a load switch, such as this MIC2090/91 (rated for 50 and 100 mA continuous current, respectively). If your current consumption is higher than that (which you say might be), I am sure you can find equivalent options. These have a very low quiescent current of 5 uA, so very respectable. This is a high side load switch, so it is easier to make sure you are actually cutting power from the modules (sometimes cutting GND doesn't do the trick).

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