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MOSFET Power Circuitry Fails if I2C Pins Initialized First.

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   I have this MOSFET Power Circuitry connected to LIS3DH Accelerometer. The LIS3DH Accelerometer is connected to TI BLE CC2640R2F. The expected behaviour is if ACC_VCC is 0, it will power on the LIS3DH Accelerometer, and if ACC_VCC is 1, it will turn off the LIS3DH Accelerometer. However, if I initialize the open the I2C pins at program initialization by calling SensorI2C_open();. This is the behavior below. By normal knowledge The I2C pins connected to the LIS3DH Accelerometer should not affect the MOSFET Power Circuitry. I suspect the MOSFET Power Circuitry is wrong. Can anyone here give me tips what could be wrong.

1.      Set ACC_VCC to 1, to turn off accelerometer.

2.      VACC is measured at 3.2 V, which should not be.

3.      Set ACC_VCC to 0, to turn on accelerometer.

4.      VACC is measured at 3.2V, which is correct.

Attached is the Accelerometer Circuitry..




accelerometer I2C.jpg

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Please see table 9 of the LIS3DH datasheet; you are not allowed to apply voltages greater than 0.3 V to the SDA/SCL pins when VACC = 0 V.

You must disconnect these signals before powering down the chip. (And when it's powered down, ACC_INT1 might be floating; you have to deal with that.)

I'd guess VACC gets powered through R8/R9, or through the chip's ESD protection diodes (which go from any I/O to VDD).

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Hi Clavier,

     Thanks for your reply. You are correct. So, these below are the sequences that I will do when powering on and powering off the LIS3DH Accelerometer.

      Powering On:

  1. Set ACC_VCC to 0, to turn on power to LIS3DH Accelerometer.
  2. Call SensorI2C_open().
  3. Enable ACC_INT1 Pin.

      Powering Off:

  1. Disable ACC_INT1 Pin.
  2. Call SensorI2C_close().
  3. Set ACC_VCC to 1, to turn off power to LIS3DH Accelerometer.

Best Regards,



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