18.1 Digital Accelerometer

Features

• Ultralow power: as low as 23 µA in measurement mode and
  • µA in standby mode at V_S = 2.5 V (typical)
• Power consumption scales automatically with bandwidth
• User-selectable resolution
• Fixed 10-bit resolution
• Full resolution, where resolution increases with g range, up to 13-bit resolution at ±16 g (maintaining 4 mg/LSB scale factor in all g ranges)
• Patent pending, embedded memory management system with FIFO technology minimizes host processor load
• Single tap/double tap detection
• Activity/inactivity monitoring
• Free-fall detection
• Supply voltage range: 2.0 V to 3.6 V I/O voltage range: 1.7 V to V_S
• SPI (3- and 4-wire) and I²C digital interfaces

Table 6: Block Diagram of ADXL345

• Flexible interrupt modes mappable to either interrupt pin Measurement ranges selectable via serial command Bandwidth selectable via serial command
• Wide temperature range (−40°C to +85°C)
• 10,000 g shock survival
• Pb free/RoHS compliant
• Small and thin: 3 mm × 5 mm × 1 mm LGA package

Applications

• Handsets Medical instrumentation
• Gaming and pointing devices
• Industrial instrumentation Personal navigation devices
• Hard disk drive (HDD) protection

General Description

The ADXL345 is a small, thin, ultralow 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 (3.9 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 by comparing the acceleration on any axis with user-set thresholds. Tap sensing detects single and double taps in any direction. Freefall sensing detects if the device is falling. These functions can be mapped individually to either of two interrupt output pins. An integrated, patent pending memory management system with a 32-level first in, first out (FIFO) buffer can be used to store data to minimize host processor activity and lower overall system power consumption.

Figure 61: ADXL345

Low power modes enable intelligent motion-based power management with threshold sensing and active acceleration measurement at extremely low power dissipation. The ADXL345 is supplied in a small, thin, 3 mm × 5 mm × 1 mm, 14-lead, plastic package.

Specifications

TA = 25°C, VS = 2.5 V, VDD I/O = 1.8 V, acceleration = 0 g, CS = 10 µF tantalum, CI/O = 0.1 µF, output data rate (ODR) = 800 Hz, unless otherwise noted. All minimum and maximum specifications are guaranteed. Typical specifications are not guaranteed. Table 1.

Table 7: Specifications of ADXL345

Table 8: Parameters of ADXL345

1. The typical specifications shown are for at least 68% of the population of parts and are based on the worst case of mean ±1 σ, except for 0 g output and sensitivity, which represents the target value. For 0 g offset and sensitivity, the deviation from the ideal describes the worst case of mean ±1 σ.
2. Cross-axis sensitivity is defined as coupling between any two axes.
3. Bandwidth is the −3 dB frequency and is half the output data rate, bandwidth = ODR/2.

Absolute Maximum Ratings

1. The output format for the 3200 Hz and 1600 Hz ODRs is different than the output format for the remaining ODRs. This difference is described in the Data Formatting of Upper Data Rates section.
2. Output data rates below 6.25 Hz exhibit additional offset shift with increased temperature, depending on selected output data rate. Refer to the Offset Performance at Lowest Data Rates section for details.

Pin Configuration and Function Descriptions

ADXL345

TOP VIEW

(Not to Scale)

SCL/SCLK

Table 9: Pin Configuration of ADXL345

Pin Function Descriptions