ADXL366 datasheet(27/71 Pages) AD

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Data Sheet

ADXL366

ADDITIONAL FEATURES

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Rev. 0 | 27 of 71

BROWNOUT RECOVERY

In the event of a brownout condition, the ADXL366 is capable to

recovering with a simple software reset command, which mean that

there is no need to perform a full hardware reset on either the

SPI or I2C mode. To perform a software reset, write 0x52 to the

SOFT_RESET register, Register 0x1F, as described in Soft Reset

Z-AXIS NONLINEARITY COMPENSATION

The ADXL366 out-of-plane (Z-axis output) response is dominated

by second-order nonlinearity due to its trampoline nature, and its

nonlinearity is usually much larger than the X-axis and Y axis

nonlinearities.

The ADXL366 counts with a digital feature that, if enabled, applies

a second-order correction to the Z-axis acceleration signal path that

can improve the nonlinearity by approximately 8×. The compensa-

tion function is as follows:

AZ, LIN=AZ, BC−k×AZ, BC2

(4)

where:

AZ, LIN is the linearized acceleration in the Z-axis.

AZ, BC is the acceleration in the Z-axis before compensation.

k is the compensation coefficient.

To enable the Z-axis nonlinearity compensation feature, set the

NL_COMP_EN bit (Bit 7) to high in Register TEMP_CTL (Register

0x3D).

Notice that the nonlinearity compensation feature does not apply

for the X-axis, Y-axis, and temperature data. Figure 52 shows an

example of the linearity improvement for the 2g range.

Figure 52. Compensated vs. Noncompensated Z-Axis Nonlinearity, 2g Range,

Sample Size = 10

FREE FALL DETECTION

Many digital output accelerometers include a built-in free fall detec-

tion feature. In the ADXL366, this function can be implemented

using the inactivity interrupt. Refer to the Implementing Free Fall

Detection section for more details, including suggested threshold

and timing values.

TAP DETECTION

The tap interrupt function is capable of detecting either single tap or

double tap events while only increasing the current consumption by

35nA when enabled. The following parameters are shown in Figure

53 for a valid single and valid double tap event:

►

The tap detection threshold is defined by the THRESH_TAP

►

The maximum tap duration time is defined by the TAP_DUR

►

The tap latency time is defined by the TAP_LATENT register

(Register 0x31) and is the waiting period from the end of the first

tap until the start of the time window when a second tap can be

detected, which is determined by the value in the TAP_WINDOW

►

The interval after the latency time (set by the TAP_LATENT reg-

ister) is defined by the window register. Although a second tap

must begin after the latency time has expired, it does not have to

finish before the end of the time defined by the TAP_WINDOW

Figure 53. Tap Interrupt Function with Valid Single and Double Taps

If only the single tap function is in use, the single tap interrupt is

triggered when the acceleration goes to less than the threshold, as

long as the value of the time stored in the TAP_DUR register was

not exceeded. If both single tap and double tap functions are in

use, the single tap interrupt is triggered when the double tap event

is either validated or invalidated, and the single tap events must

be cleared (by reading the STATUS2 register) to allow the next tap

(double tap) events to be detected.

Note that when using a tap threshold (the THRESH_TAP register)

less than 1g, tilting the device may also result in a tap event.

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