Terminology

AN3182

4/18

Doc ID 17289 Rev 1

1

Terminology

Low-g MEMS accelerometers are widely used for tilt sensing in consumer electronics and

industrial applications, such as screen rotation and automobile security alert systems.

Another popular application for low-g accelerometers is tilt compensated electronic

compasses for map rotation and personal navigation devices. This application note

describes how to obtain accurate tilt measurements with respect to local Earth horizontal

plane, by compensating for a few non idealities that may cause angular tilt calculation error.

In this document, the 3-axis digital accelerometer LIS331DLH is used as an example. For

detailed information and device specifications, refer to the LIS331DLH datasheet available

accordance with their respective specifications.

1.1

Accelerometer datasheet

When designing a tilt sensing system, the first step is to examine the accelerometer

specifications and understand the meaning of each parameter that affects tilt sensing

accuracy. Table 1 shows the main parameters of the LIS331DLH 3-axis digital

accelerometer when a full-scale of ±2 g is selected, which is optimum for tilt sensing

applications. Note that higher full-scale ranges can also be selected for tilt sensing, but

accuracy is affected by the resulting lower sensitivity.

Table 1.

Main parameters for the LIS331DLH @ Vdd = 2.5 V, T = 25 °C

Symbol

Parameter

Test conditions

Min.

Typ.

Max.

Unit

Vdd

Power supply

2.16

2.5

3.6

V

Idd

Current consumption in

normal mode

250

µA

ODR

Output data rate in normal

mode

Selectable by DR bits

in CTRL_REG1

50/100/400/

1000

Hz

BW

System bandwidth

ODR/2

Hz

Ton

Turn-on time

ODR = 100 Hz

1/ODR + 1

ms

Top

Operating temperature

range

-40

+85

°C

FS

Full-scale measurement

rage

FS bit set to 00

±2.0

g

So

Sensitivity

FS bit set to 00

12-bit representation

0.9

1

1.1

mg/LSB

TCSo

Sensitivity change vs.

temperature

FS bit set to 00

±0.01

%/°C

TyOff

Typical zero-g level offset

accuracy

FS bit set to 00

±20

mg

TCOff

Zero-g level change vs.

temperature

Max delta from 25 °C

±0.1

mg/°C

An

Acceleration noise density

FS bit set to 00

218

μg

(

)

Hz

()

⁄