MMA8450QT datasheet(15/57 Pages) FREESCALE

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Sensors

Freescale Semiconductor

MMA8450Q

5.8

Orientation Detection

The MMA8450Q incorporates an advanced algorithm for orientation detection (ability to detect all 6 orientations including

portrait/landscape) with a large amount of configuration available to provide extreme flexibility to the system designer. The

configurability also allows for the function to work differently for various modes of the end system. For example, the MMA8450Q

Orientation Detection allows up to 10 selectable trip angles for Portrait-to-Landscape, up to10 selectable trip angles for the

transition for Landscape-to-Portrait, and 4 selectable front/back trip angles. Typically the desired hysteresis angle is ±15° from a

45° trip reference point, resulting in |30°| and |60°| trip points. The algorithm is robust enough to handle typical process variation

and uncompensated board mount offset, however, it may result in slight angle variations.

The MMA8450Q Orientation Detection algorithm confirms the reliability of the function with a configurable Z-lock out angle.

Based on known functionality of linear accelerometers, it is not possible to rotate the device about the Z-axis to detect change in

acceleration at slow angular speeds. The angle at which the image no longer detects the orientation change is referred to as the

“Z-Lock- out angle”. The MMA8450Q Orientation Detection function has eight selectable1g-lockout thresholds; and there are 8

different settings for the Z-Angle lockout.

The Orientation Detection function also considers when a device is experiencing acceleration above a set threshold not typical

of orientation changes (i.e., When a person is jogging or due to acceleration changes from being on a bus or in a car). The screen

orientation should not interpret this as a change and the screen should lock in the last known valid position. This added feature,

called the 1g Lockout Threshold, enhances the Orientation Detection function and confirms the reliability of the algorithm for the

system. The MMA8450Q allows for configuring the 1g Lockout Threshold from 1g up to 1.35g (in increments of 0.05g).

For further information on the highly configurable embedded Orientation Detection Function, including recommendations for

configuring the device to support various application use cases, refer to Freescale application note, AN3915.

Figure 6 and Figure 7 show the definitions of the trip angles going from Landscape-to-Portrait and then also from Portrait-to-

Landscape.

Figure 6. Illustration of Landscape-to-Portrait Transition

Figure 7. Illustration of Portrait-to-Landscape Transition

Figure 8 illustrates the Z-angle lockout region. When lifting the device up from the flat position it will be active for orientation

detection as low as 25° from flat. This is user configurable. The default angle is 32° but it can be set as low as 25°.

Figure 8. Illustration of Z-Tilt Angle Lockout Transition

PORTRAIT

Landscape-to-Portrait

Trip Angle = 60

0° Landscape

PORTRAIT

Portrait-to-Landscape

Trip Angle = 60

0° Landscape

PORTRAIT

NORMAL

ZLOCK = 32.142°

0° Landscape

DETECTION

REGION

LOCKOUT

REGION

MMA8450QT Datasheet(PDF) 15 Page - Freescale Semiconductor, Inc

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