MMA8653FC datasheet(14/56 Pages) FREESCALE

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MMA8653FC

Sensors

Freescale Semiconductor, Inc.

5.3

Low power modes vs. high resolution modes

The MMA8653FC can be optimized for lower power modes or for higher resolution of the output data. One of the oversampling

schemes of the data can activated when MODS = 10 in Register 0x2B, which will improve the resolution of the output data only.

The highest resolution is achieved at 1.56 Hz.

There is a trade-off between low power and high resolution. Low power can be achieved when the oversampling rate is

reduced. When MODS = 11, the lowest power is achieved. The lowest power is achieved when the sample rate is set to 1.56 Hz.

5.4

Auto-WAKE/SLEEP mode

The MMA8653FC can be configured to transition between sample rates (with their respective current consumption) based on

four of the interrupt functions of the device. The advantage of using the Auto-WAKE/SLEEP is that the system can automatically

transition to a higher sample rate (higher current consumption) when needed, but spends the majority of the time in the SLEEP

mode (lower current) when the device does not require higher sampling rates.

•

Auto-WAKE refers to the device being triggered by one of the interrupt functions to transition to a higher sample rate. This

may also interrupt the processor to transition from a SLEEP mode to a higher power mode.

•

SLEEP mode occurs after the accelerometer has not detected an interrupt for longer than the user-definable timeout period.

The device will transition to the specified lower sample rate. It may also alert the processor to go into a lower power mode, to

save on current during this period of inactivity.

The interrupts that can WAKE the device from SLEEP are the following: Orientation detection, and Freefall/Motion detection. The

interrupts that can keep the device from falling asleep are the same interrupts that can wake the device.

5.5

Freefall detection

MMA8653FC has a flexible interrupt architecture for detecting either a Freefall or a Motion.

•

Freefall can be enabled where the set threshold must be less than the configured threshold.

•

Motion can be enabled where the set threshold must be greater than the configured threshold.

8-bit Data

Range ±2g (15.6 mg)

Range ±4g (31.25 mg)

Range ±8g (62.5 mg)

0111 1111

1.984g

+3.968g

+7.937g

0111 1110

1.968g

+3.937g

+7.875g

……

…

0000 0001

+0.015g

+0.031g

+0.062g

0000 0000

0.000g

1111 1111

-0.015g

-0.031g

-0.062g

……

…

1000 0001

-1.984g

-3.968g

-7.937g

1000 0000

-2.000g

-4.000g

-8.000g

Table 9. Accelerometer 8-bit output data

8-bit Data

Range ±2g (15.6 mg)

Range ±4g (31.25 mg)

Range ±8g (62.5 mg)

0111 1111

1.9844g

+3.9688g

+7.9375g

0111 1110

1.9688g

+3.9375g

+7.8750g

……

…

0000 0001

+0.0156g

+0.0313g

+0.0625g

0000 0000

0.000g

0.0000g

1111 1111

-0.0156g

-0.0313g

-0.0625g

……

…

1000 0001

-1.9844g

-3.9688g

-7.9375g

1000 0000

-2.0000g

-4.0000g

-8.0000g

Table 8. Accelerometer 10-bit output data (Continued)

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