KX022-1020 Datasheet, PDF (60/75 Pages) List of Unclassifed Manufacturers – Accelerometer Specifications

± 2g / 4g / 8g Tri-axis Digital
Accelerometer Specifications
PART NUMBER:
KX022-1020
Rev. 11.0
10-Sep-15
Motion Interrupt Feature Description
The Motion interrupt feature of the KX022 reports qualified changes in the high-pass filtered acceleration
based on the Wake Up (ATH) threshold. If the high-pass filtered acceleration on any axis is greater than the
user-defined wake up threshold (ATH), the device has transitioned from an inactive state to an active state.
Equation 4 shows how to calculate the ATH register value for a desired wake up threshold. Note that this
calculation varies based on the configured g-range of the part.
ATH (counts) = Wake Up Threshold (g) x 16 (counts/g)
Equation 4: Wake Up Threshold
An 8-bit raw unsigned value represents a counter that permits the user to qualify each active/inactive state
change. Note that each WUFC Timer count qualifies 1 (one) user-defined ODR period (OWUF). Equation 5
shows how to calculate the WUFC register value for a desired wake up delay time.
WUFC (counts) = Wake Up Delay Time (sec) x OWUF (Hz)
Equation 5: Wake Up Delay Time
The latched motion interrupt response algorithm works as following: while the part is in inactive state, the
algorithm evaluates differential measurement between each new acceleration data point with the preceding
one and evaluates it against the ATH threshold. When the differential measurement is greater than ATH
threshold, the wakeup counter starts the count. Differential measurements are now calculated based on the
difference between the current acceleration and the acceleration when the counter started. The part will report
that motion has occurred at the end of the count assuming each differential measurement has remained above
the threshold. If at any moment during the count the differential measurement falls below the threshold, the
counter will stop the count and the part will remain in inactive state.
To illustrate how the algorithm works, consider the Figure 10 below that shows the latched response of the
motion detection algorithm with WUF Timer (WUFC) set to 10 counts. Note how the difference between the
acceleration sample marked in red and the one marked in green resulted in a differential measurements
represented with orange bar being above the WUF threshold. At this point, the counter begins to count number
of counts stored in WUFC register and the wakeup algorithm will evaluate the difference between each new
acceleration measurement and the measurement marked in green that will remain a reference measurement
for the duration of the counter count. At the end of the count, assuming all differential measurements were
larger than WUF threshold, as is the case in the example showed in Figure 10, a motion event will be reported.
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