INTRODUCTION
The ADXL345 is a small, thin, low power,
3-axis accelerometer with high resolution (13-bit)measurement at up to ±16 g.
Digital output data is formatted as 16-bit twos complement and is accessible
through either a SPI (3- or 4-wire) or I2C digital interface. The ADXL345 is
well suited for mobile device applications. It measures the static acceleration
of gravity in tilt-sensing applications, as well as dynamic acceleration
resulting from motion or shock. Its high resolution (4 mg/LSB) enables
measurement of inclination changes less than 1.0°. Several special sensing functions
are provided. Activity and inactivity sensing detect the presence or lack of
motion and if the acceleration on any axis exceeds a user-set level. Tap
sensing detects single and double taps. Free-fall sensing detects if the device
is falling. These functions can be mapped to one of two interrupt output pins.
An integrated, patent pending 32-level first in, first out (FIFO) buffer can be
used to store data to minimize host processor intervention. Low power modes
enable intelligent motion based power management with threshold sensing and
active acceleration measurement at extremely low power dissipation.
FEATURES
- Ultralow power: as low as 40µA in measurement mode and µA in stand by mode.
- Power consumption scales automatically with bandwidth user selectable resolution.
- Embedded, patent pending FIFO technology minimizes host processor load tap/double tap detection.
- Activity/inactivity monitoring.
- Free fall detection.
- SPI and I2C digital interfaces.
- Measurement ranges selectable via serial command.
- Bandwidth selectable via serial command.
- Pb free/RoHS compliant.
- 10,000g shock survival
APPLICATIONS
- Handsets.
- Medical instrumentation.
- Gaming and pointing devices
PIN DETAIL
SPECIFICATIONS
WORKING
The ADXL345 is a complete 3-axis acceleration measurement system with a
selectable measurement range of ±2 g, ±4 g, ±8 g, or ±16 g. It measures both
dynamic acceleration resulting from motion or shock and static acceleration,
such as gravity, that allows the device to be used as a tilt sensor. The sensor
is a poly silicon surface-micro machined structure built on top of a silicon
wafer. Poly silicon springs suspend the structure over the surface of the wafer
and provide a resistance against forces due to applied acceleration. Deflection
of the structure is measured using differential capacitors that consist of
independent fixed plates and plates attached to the moving mass. Acceleration
deflects the proof mass and unbalances the differential capacitor, resulting in
a sensor output whose amplitude is proportional to acceleration.
Phase-sensitive demodulation is used to determine the magnitude and polarity of
the acceleration. Power can be applied to VS or VDD I/O in any sequence without
damaging the ADXL345. The interface voltage level is set with the interface
supply voltage, VDD I/O, which must be present to ensure that the ADXL345 does
not create a conflict on the communication bus. For single-supply operation,
VDD I/O can be the same as the main supply, VS. In a dual-supply application,
however, VDD I/O can differ from VS to accommodate the desired interface
voltage, as long as VS is greater than or equal to VDD I/O. After VS is
applied, the device enters standby mode, where power consumption is minimized
and the device waits for VDD I/O to be applied and for the command to enter
measurement mode to be received. In addition, while the device is in standby
mode, any register can be written to or read from to configure the part. It
is recommended to configure the device
in standby mode and then to enable measurement mode. Clearing the measure bit
returns the device to the standby mode.
