AN4662 datasheet(9/43 Pages) STMICROELECTRONICS

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AN4662

Operating modes

2.1

Power-down mode

When the device is in power-down mode, almost all internal blocks of the device are

switched off to minimize power consumption. Digital interfaces (I

2C and SPI) are still active

to allow communication with the device. The content of the configuration registers is

preserved and the output data registers are not updated, therefore keeping the last data

sampled in memory before going into power-down mode.

During power-down mode the Interrupt pins continue to be driven at the last logical state.

2.2

Active mode

In active mode, data are generated at the output data rate (ODR) selected through the

ODR[2:0] bits of CTRL1 register. Six different ODRs can be selected in order to guarantee

desired application bandwidth: 800 Hz, 400 Hz, 200 Hz, 100 Hz, 50 Hz and 10 Hz.

The three acceleration axes can be individually enabled through the Zen, Yen, and Xen bits

of CTRL1 register. All combinations of single, two or three axes can be applied; output

registers related to disabled axes are forced to value 0000h.

Data interrupt generation and the FIFO buffer are active and configurable respectively

through the IG_CFGx (30h, 36h) and FIFO_CTRL (2Eh) registers.

The Activity/Inactivity recognition function can be enabled to reduce system power

consumption.

2.3

Data stabilization time

The LIS2HH12 reading chain contains low-pass filtering to improve signal-to-noise

performance and to reduce aliasing effects. For this reason the settling time of the filters

must be considered when the device is switched from power-down to active mode or when

the ODR is changed.

Table 4: "Number of samples to be discarded" clarifies the number of samples to be

discarded depending on the internal filter bandwidth and output data rate selection.

Bandwidth can be changed by setting the BW [2:1] bits in CTRL4 register and the output

data rate can be changed by setting the ODR [2:0] bits in CTRL1.

Table 4: Number of samples to be discarded

ODR [Hz]

BW = 400 Hz

BW = 200 Hz

BW = 100 Hz

BW = 50 Hz

100

200

400

800

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