IIS328DQ datasheet(14/40 Pages) STMICROELECTRONICS

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Mechanical and electrical specifications

IIS328DQ

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DocID027250 Rev 3

2.5.2

Zero-g level

Zero-g level offset (TyOff) describes the deviation of an actual output signal from the ideal

output signal if no acceleration is present. A sensor in a steady-state on a horizontal surface

measures 0 g on the X-axis and 0 g on the Y-axis, whereas the Z-axis measures 1 g. The

output is ideally in the center of the dynamic range of the sensor (the content of the OUT

registers is 00h, data expressed as 2’s complement number). A deviation from the ideal

value in this case is called zero-g offset. Offset is, to some extent, a result of stress to the

MEMS sensor and therefore the offset can slightly change after mounting the sensor onto a

printed circuit board or exposing it to extensive mechanical stress. Offset changes little over

temperature, see “Zero-g level change vs. temperature” in Table 3. The zero-g level

tolerance (TyOff) describes the standard deviation of the range of zero-g levels of a

population of sensors.

2.5.3

Self-test

Self-test allows the sensor functionality to be tested without moving it. The self-test function

is off when the self-test bit (ST) of CTRL_REG4 (control register 4) is programmed to ‘0‘.

When the self-test bit of CTRL_REG4 is programmed to ‘1’, an actuation force is applied to

the sensor, simulating a definite input acceleration. In this case, the sensor outputs exhibit a

change in their DC levels which are related to the selected full scale through the device

sensitivity.

When the self-test is activated, the device output level is given by the algebraic sum of the

signals produced by the acceleration acting on the sensor and by the electrostatic test force.

If the output signals change within the amplitude specified in Table 3, then the sensor is

working properly and the parameters of the interface chip are within the defined

specifications.

2.5.4

Sleep-to-wakeup

The “sleep-to-wakeup” function, in conjunction with low-power mode, allows further

reduction of system power consumption and development of new smart applications. The

IIS328DQ may be set to a low-power operating mode, characterized by lower data rate

refresh. In this way the device, even if sleeping, continues to sense acceleration and to

generate interrupt requests.

When the “sleep-to-wakeup” function is activated, the IIS328DQ is able to automatically

wake up as soon as the interrupt event has been detected, increasing the output data rate

and bandwidth.

With this feature, the system may be efficiently switched from low-power mode to full-

performance depending on user-selectable positioning and acceleration events, therefore

ensuring power saving and flexibility.

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