mma8451 power consumption

[markross-smith]

Hi,

I have developed a remote monitoring device that uses an MMA8451 communicating with an MSP430 microprocessor.  During development I used the MMA8451 on a breakout board, the intention being to use the "raw" chip in the production version.

The power consumption through the MMA8451 is 29uA which is very different from the 6uA I was expecting from the settings I am using.  My settings are:

 // ******************* Start Transient Detection ***********************
Transmit(CTRL_REG1, 0x18);                   // Enable Standby mode
Transmit(TRANSIENT_CFG, 0x08);          // Enable Transient Detection Z axis only
Transmit(TRANSIENT_THS, 0x03);          // Set Threshold >0.2G
Transmit(TRANSIENT_COUNT, 0x01);    // Set Debounce counter 12.5Hz, 80ms (0x02 = 160ms)
Transmit(CTRL_REG3, 0x40);                  // Transient wake, push-pull, active Low interrupt
Transmit(CTRL_REG4, 0x20);                 // Set Interrupt function in System
Transmit(CTRL_REG5, 0x20);                // Set Interrupt to pin Int1
Transmit(ASLP_COUNT, 0x02);             // Set sleep count 2 x 320ms = 640ms
Transmit(CTRL_REG2, 0x1F);                // Set Sleep Mode = low power, Active mode = low power
Transmit(CTRL_REG1, 0x65);                // ODR = 12.5Hz, ODR = 50Hz, Active mode
} // **************** End Transient Detection ****************************

Is the excessive power consumption because I am using the break-out version, and can I expect something closer to 6uA in the production version?

Thanks,

Mark

[TomasVaverka]

Hi Mark,

How are you measuring this current consumption? Are not there other devices drawing current as well?

Also be aware that the current consumption stated in the datasheet applies for VDD = 2.5V and has been measured with an amperemeter between 2.5V voltage rail and VDD input only (not VDDIO).

Best regards,

Tomas

[markross-smith]

Hi Tomas,

I am using my DMM in line between the +3V supply rail and the VIn pin.  The overall power consumption to the microprocessor and MMA8451 is about 32uA, of which 29uA is going to the MMA.

Have I used the correct register settings for the MMA to achieve the 6uA that the tech docs suggest?

Thanks,

Mark 

[TomasVaverka]

Hi Mark,

You should be able to achieve the current consumption outlined in the datasheet with that register settings. You may refer to this example project where we achieved even lower values than specified in the datasheet. 

Best regards,

Tomas

[markross-smith]

Hi Tomas,

Thanks for the example. As far as I can see, I am already using the correct settings for the 6uA consumption.  I just hope that I can achieve that once I have built the prototype using a "raw" MMA8451.

Cheers,

Mark