Terminology

AN4508

4/13

DocID026444 Rev 1

1

Terminology

1.1

Accelerometer datasheet

The first step is to examine the accelerometer specifications and understand the meaning of

each parameter.

Understanding the parameters



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

supply. Correct operation of the accelerometer using a power supply voltage outside of

this range is not guaranteed. The parameters are provided by the accelerometer

manufacturer under Vdd = +2.5 V at a room temperature of T = 25 °C. It is

recommended to keep 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.



Idd - Current consumption in normal mode: lower ODR corresponds to lower current

consumption.



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

data rates in normal mode from which the user may select.



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

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

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

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

useful system signals.



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.



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.



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 device to a higher full-scale

range which results in lower sensitivity.



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

digital representation.



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.



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

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