ADXL362BCCZ-R2 datasheet(37/44 Pages) AD

37 / 44 page

Data Sheet

ADXL362

Rev. B | Page 37 of 44

Example: Implementing Free Fall Detection

Many digital output accelerometers include a built-in free fall

detection feature. In the ADXL362, implement this function

using the inactivity interrupt.

When an object is in true free fall, acceleration on all axes is 0 g.

Thus, free fall detection is achieved by looking for acceleration

on all axes to fall below a certain threshold (close to 0 g) for a

certain amount of time. The inactivity detection functionality,

when used in absolute mode, does exactly this.

To use inactivity to implement free fall detection, set the value

in THRESH_INACT to the desired free fall threshold. Values

between 300 mg and 600 mg are recommended; the register

setting for these values varies based on the g range setting of the

device, as follows:

THRESH_INACT =

Threshold Value [g] × Scale Factor [LSB per g]

Set the value in TIME_INACT to implement the minimum

amount of time that the acceleration on all axes must be less

than the free fall threshold to generate a free fall condition.

Values between 100 ms and 350 ms are recommended; the

TIME_INACT = Time [sec] × Data Rate [Hz]

When a free fall condition is detected, the inactivity status is set

to 1 and, if the function is mapped to an interrupt pin, an

inactivity interrupt triggers on that pin.

Startup Routine

The following startup routine configures the ADXL362 for a

typical free fall application. This routine assumes a ±8 g

measurement range and 100 Hz output data rate. Thresholds

and timing values can be modified to suit particular application

needs.

1. Write 0x96 (150 codes) to Register 0x23: sets free fall

threshold to 600 mg.

2. Write 0x03 to Register 0x25: sets free fall time to 30 ms.

3. Write 0x0C to Register 0x27: enables absolute inactivity

detection.

4. Write 0x20 to Register 0x2A or Register 0x2B to map the

inactivity interrupt to INT1 or INT2, respectively.

5. Write 0x83 to Register 0x2C: configures the accelerometer

to ±8 g range, 100 Hz ODR (output data rate).

6. Write 0x02 to Register 0x2D to begin measurement.

Implementation of a complete fall detection application is

described in the AN-1023 Application Note, Fall Detection

Application by Using 3-Axis Accelerometer ADXL345.

POWER

Power Supply Decoupling

Figure 46 shows the recommended bypass capacitors for use

with the ADXL362.

ADXL362

GND

INT1

INT2

SCLK

MISO

MOSI

SPI

INTERFACE

VDD I/O

CIO

INTERRUPT

CONTROL

Figure 46. Recommended Bypass Capacitors

A 0.1 µF ceramic capacitor (CS) at VS and a 0.1 µF ceramic capacitor

(CIO) at VDDI/O placed as close as possible to the ADXL362. Supply

pins are recommended to adequately decouple the accelerometer

from noise on the power supply. It is also recommended that VS

and VDD I/O be separate supplies to minimize digital clocking

noise on the VS supply. If this is not possible, additional filtering

of the supplies may be necessary.

If additional decoupling is necessary, place a resistor or ferrite bead,

no larger than 100 Ω, in series with VS. Additionally, increasing the

bypass capacitance on VS to a 1 µF tantalum capacitor in parallel

with a 0.1 µF ceramic capacitor may also improve noise.

Ensure that the connection from the ADXL362 ground to the

power supply ground has low impedance because noise transmitted

through ground has an effect similar to noise transmitted through VS.

Power Supply Requirements

The ADXL362 is designed to operate using supply voltage rails

ranging from 1.8 V to 3.3 V. The operating voltage range (VS),

specified in Table 1, ranges from 1.6 V to 3.5 V to account for

inaccuracies and transients of up to ±10% on the supply voltage.

The ADXL362 does not require any particular startup transient

characteristics, except that it must always be started up from 0 V.

When the device is in operation, any time power is removed

from the ADXL362, or falls below the operating voltage range,

the supplies (VS, VDD I/O, and any bypass capacitors) must be

discharged completely before power is reapplied. To enable

supply discharge, it is recommended to power the device from

a microcontroller GPIO, connect a shutdown discharge switch

to the supply (Figure 47), or use a voltage regulator with a

shutdown discharge feature, such as the ADP160.

ADXL362

GND

INT1

SHUTDOWN

NOTES

1. THE ADXL362 SUPPLIES MUST BE DISCHARGED FULLY EACH TIME

THE VOLTAGE ON THEM DROPS BELOW THE SPECIFIED OPERATING

RANGE. A SHUTDOWN SWITCH IS ONE WAY TO DISCHARGE THE SUPPLIES.

VIN

INT2

SCLK

MISO

MOSI

SPI

INTERFACE

VDD I/O

CIO

Figure 47. Using a Switch to Discharge the ADXL362 Supplies

ADXL362BCCZ-R2 数据表(PDF) 37 Page - Analog Devices

ADXL362BCCZ-R2 数据表(HTML) 37 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

数据表下载

链接网址

ADXL362BCCZ-R2 数据表(PDF) 37 Page - Analog Devices

ADXL362BCCZ-R2 数据表(HTML) 37 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

数据表 下载

链接网址

数据表下载