MMA8453 Transient detection

[georgek]

Hi,

In regards to reading the actual acceleration data of an MMA8453, would I need to take into consideration the reference gravitational force?  For example, in reference to Figure 3 in the MMA8453Q datasheet, the "SIDE, FRONT" view shows 1g in the Z direction. If the device is set for a transient detection value of 2g, would the device be triggered at a Z force of 2g, or 3g, since there is already a 1g force, due to gravity? Will the data in the Zout register read the actual value of the force, or will the data be compensated for according to the 1g reference?

Thanks in advance for your advice,

George

[TomasVaverka]

Hi George,

The embedded transient detection function uses the high-pass filtered data unless the HPF_BYP bit in the TRANSIENT_CFG register (0x1D) is set. So if HPF_BYP = 0, the transient detection function compares whether any of the enabled axes has exceeded a set change in acceleration disregarding the static acceleration. Please refer to the AN4071 for more information.

However, compared with both the MMA8451Q and MMA8452Q, the MMA8453Q does not allow to set the high-pass filter for the output data using the HPF_OUT bit in the XYZ_DATA_CFG register (0x0E), so the data registers 0x01 - 0x06 will not contain high-pass filtered data.

I hope it helps.

Regards,

Tomas