AN3182

Terminology

Doc ID 17289 Rev 1

5/18

1.2

Understanding the parameters

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Vdd - Power supply: This parameter defines the accelerometer operating DC power

supply range between +2.16 V and +3.6 V (typical +2.5 V). Correct operation of the

accelerometer using a power supply voltage outside of this range is not guaranteed.

The parameters in Table 1 are provided by the accelerometer manufacturer under

Vdd = +2.5 V at a room temperature of T = 25 °C. It is recommended to keep the Vdd

clean, with minimum ripple. One possible way to do this is to use an ultra low-noise low-

dropout regulator to power the accelerometer.

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Idd - Current consumption in normal mode: In the case of the LIS331DLH, lower ODR

corresponds to lower current consumption.

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ODR - Output data rate in normal mode: This parameter shows the possible output

data rates in normal mode. The user can select different ODR by setting the DR bits in

the CTRL_REG1 register.

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BW - System bandwidth: This parameter defines the bandwidth of the system. When

ODR = 100 Hz, BW is typically 50 Hz with built-in low pass filter. The system

recognizes any motion below 50 Hz. If the system has dynamic motion higher than

50 Hz, then ODR needs to be increased to a higher setting in order to cover all useful

system signals.

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Ton - Turn-on time: This parameter defines the time required before the accelerometer

is ready to output measured acceleration data after exiting power-down mode. For

example, at ODR = 100 Hz, the user should wait for a minimum of 1/100 + 1 = 11 ms

after exiting from power-down mode before sampling the accelerometer data.

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Top - operating temperature range: This parameter defines the operating temperature

range. When the device is operated inside the specified range, proper behavior of the

sensor is guaranteed.

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FS - Full-scale measurement range: For tilt sensing applications, a ±2.0 g range is

sufficient because the Earth’s gravity is ±1 g only. If the application requires

measurement of higher g acceleration, the user can set the LIS331DLH to a higher full-

scale range of ±4.0 g or ±8.0 g, which results in lower sensitivity.

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So - Sensitivity: This parameter defines the value of 1LSB with respect to mg in the

digital representation. For example, at ±2.0 g full-scale range, the sensitivity is typically

about 1 mg/LSB at 12-bit representation. Therefore, when the sensor is stable on a

horizontal surface, the Z axis output is around 1000LSB.

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TCSo - Sensitivity change vs. temperature: This parameter defines how sensitivity

changes with temperature. For example, at a ±2.0 g full-scale range, the sensitivity

changes within ±0.01%/°C. Therefore, if the environmental temperature changes 40 °C,

from 25 °C to 65 °C, then the sensitivity changes within the range of ±0.01% * 40 =

±0.4%, which means the sensitivity change over 40 °C is within 0.996 mg/LSB and

1.004 mg/LSB, which shows that the sensitivity is very stable versus temperature

change. Thus, temperature compensation for sensitivity can be ignored.

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TyOff - Typical zero-g level offset accuracy: This parameter defines the zero-g accuracy

at a room temperature of 25 °C. For example, at a ±2.0 g full-scale range, the zero-g

accuracy of ±20 mg means that the zero-g output varies typically in the range of ±20

mg around the expected ideal value.

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TCOff - Zero-g level change vs. temperature: This parameter defines how much the

zero-g level is affected by temperature variations. For example, at ±2.0 g full-scale

range, the zero-g level changes typically within ±0.1 mg/°C. This means that if the

environmental temperature changes 40 °C, from 25 °C to 65 °C, then the zero-g level

changes within the range of ±0.1 mg * 40 = ±4 mg, which shows that the zero-g level is