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ADXL362 Fiches technique(PDF) 10 Page - Analog Devices |
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ADXL362 Fiches technique(HTML) 10 Page - Analog Devices |
10 / 40 page ADXL362 Preliminary Technical Data Rev. PrB | Page 10 of 40 POWER SAVINGS FEATURES The ADXL362 was designed for the most power-conscious applications, and as such includes several features, described in this section, for enabling power savings at the system level as well as at the device level. ULTRA-LOW POWER CONSUMPTION IN ALL MODES At the device level, the most obvious power saving feature of the ADXL362 is its ultra-low current consumption in all configurations: the ADXL362 consumes between 1.1 µA (typ) and 5 µA (typ) across all data rates up to 400 Hz and all supply voltages up to 3.6V (see Figure 4). An even lower-power, 350 nA (typ) motion-triggered Wake-Up Mode is provided for simple motion detection applications that require even lower power consumption than 1 µA. At these current levels, the accelerometer consumes less power in full operation than many other system components’ standby currents, and is therefore optimal for applications that require continuous acceleration monitoring and very long battery life. As the accelerometer is always on, it can act as a motion- activated switch and signal to the rest of the system when to turn on, thereby managing power at the system level. No less important than its low operating current, the ADXL362’s 10 nA (typ) Standby current contributes to much longer battery life in applications that spend most of their time in a “sleep” state and wake up via an external trigger. MOTION DETECTION The ADXL362 features built-in logic that detects Activity (presence of acceleration above a threshold) and Inactivity (lack of acceleration above a threshold). Detection of an activity or inactivity event is indicated in the Status register and can also be configured to generate an interrupt. In addition, the activity status of the device – that is, whether it is “moving” or “stationary” – is indicated by the Awake bit, described on page 11. Activity and Inactivity detection can be used when the accelerometer is in either Measurement Mode or Wake-Up Modes. Activity Detection An Activity event is detected when acceleration stays above a specified threshold for a specified time period. Referenced and Absolute Configurations Activity detection can be configured as Referenced or Absolute. When using Absolute Activity detection, acceleration samples are compared to a user-set threshold to determine whether motion is present. For example, if a threshold of 0.5g is set and the acceleration on the z-axis is 1g for longer than the user- defined Activity time, the Activity status is asserted. In many applications, it is advantageous for activity detection to be based not on an absolute threshold but on a deviation from a reference point or orientation. This is particularly useful as it removes the effect on Activity detection of the static 1g imposed by gravity. When an accelerometer is stationary, its output can reach 1g, even when it is not moving. In Absolute Activity, if the threshold were set to less than 1g, activity would immediately be detected in this case. In the Referenced configuration, Activity is detected when acceleration samples are at least a user-set amount above an internally-defined reference, for the user-defined amount of time. The reference is calculated when Activity detection is engaged, so activity is only detected when the acceleration has deviated sufficiently from the initial orientation. The Referenced configuration results in a very sensitive Activity detection that detects even the most subtle motion events. Fewer False Positives Ideally, the intent of Activity detection is to wake up a system only when motion is intentional, ignoring noise or small, unintentional movements. In addition to being sensitive to subtle motion events, the ADXL362 Activity detection algorithm is also designed to be robust in filtering out undesired triggers. The ADXL362 activity detection functionality includes a timer that can be used to filter out unwanted motion and ensure that only sustained motion is recognized as Activity. The duration of this timer, as well as the acceleration threshold, are user- adjustable from 1 sample (i.e., no timer) to up to 20 seconds of motion. Note that the Activity timer is operational in Measurement Mode only. In Wake-Up Mode, one-sample Activity detection is used. Inactivity Detection An Inactivity event is detected when acceleration remains below a specified threshold for a specified time. Inactivity detection can also be configured as Referenced or Absolute. When using Absolute Inactivity detection, acceleration samples are compared to a user-set threshold for the user-set time to determine the absence of motion. The Absolute configuration should be used for implementing free-fall detection. When using Referenced Inactivity detection, Inactivity is detected if acceleration samples are within less than a user- specified amount of an internally-defined reference, for a user- defined amount of time. Referenced Inactivity, like Referenced Activity, is particularly useful for eliminating the effects of the 1g due to gravity. With |
Numéro de pièce similaire - ADXL362 |
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Description similaire - ADXL362 |
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