Analog Devices iMEMS ADXL372 User Manual page 11

EVAL-ADXL372Z-M
Inactivity Interrupt Configuration options (shown in
Figure 15) adjust the settings that control the level of
inactivity and how much time is required to put the device
into sleep mode. For example, the
from activity to inactivity mode when the
remains stable for a long enough time. When the
enters inactivity mode, the
while in sleep mode or while in the low speed sampling
rate mode.
Power Consumption Tab, Common Uses
Two commonly used power consumption conditions can be
applied to the ADXL372
and autosleep behavior.
Instant-On Behavior
The ADXL372 instant-on mode is an ultra low power mode
that continuously monitors the environment for impact events
that exceed a built-in threshold. When detecting an impact, the
device switches into full measurement mode and captures the
impact profile.
In Figure 16, when the acceleration is lower than the built-in
threshold, there is no digitized acceleration output and the
power consumption is lower than 2 μA. Adding a shock event
on the board to make the acceleration exceed the built-in
threshold causes the
bandwidth measurement mode and captures the impact profile.
The built-in threshold is either 10 g to 15 g or 30 g to 40 g. A
user can choose the threshold by disabling or enabling the High
Instant On Threshold checkbox. Checking High Instant On
Threshold sets the threshold at 30 g to 40 g. Unchecking High
Instant On Threshold sets the threshold at 10 g to 15 g. To use
the other threshold and still monitor the shock or vibration
event with just several μA, use the autosleep mode.
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User Guide
ADXL372 transitions
ADXL372
ADXL372 continues to operate
evaluation system: instant on behavior
ADXL372 to switch immediately into full
Figure 16. Instant-On Mode
Upon the accelerometer entering full bandwidth measurement
mode, it must be set back into instant-on mode manually by
clicking the Stop Meas button and then clicking the View Meas
button again. It cannot return to instant-on mode automatically.
Autosleep Behavior
ADXL372
To observe the behavior of the device when in autosleep mode,
apply the settings listed in Table 2.
Table 2. Recommended Settings for Autosleep Operation
Parameter
Mode of Operation
Data Rate in Full Bandwidth
Measurement Mode
Bandwidth
Wake-Up Rate
Low Noise Mode
Low-Pass Filter
High-Pass Filter
Activity Configuration
Activity Interrupt
Activity Threshold
Activity Time
Coupling
Inactivity Configuration
Inactivity Interrupt
Inactivity Threshold
Inactivity Time
Coupling
After the settings are applied, click View Meas. As shown in
Figure 17, when there is no motion to trigger the activity
interrupt the
powers down for a duration of time equal to the Wakeup
Rate (ms) setting and then turns on to sample the front end.
Rev. 0 | Page 11 of 13
Setting
Autosleep
3200 Hz
1600 Hz
512 ms
Normal operation
Enable
Disable
On
2 g
3.3 ms
AC
On
2 g
3016 ms
AC
ADXL372 works in wake-up mode. The device
Figure 17. Wake-Up Mode
UG-1237