5/14

LIS3L02AS4

3.1 Terminology

3.1.1 Sensitivity

Describes the gain of the sensor and can be determined by applying 1g acceleration to it. As the sensor

can measure DC accelerations this can be done easily by pointing the axis of interest towards the center

of the earth, note the output value, rotate the sensor by 180 degrees (point to the sky) and note the output

value again thus applying

±1g acceleration to the sensor. Subtracting the larger output value from the

smaller one and dividing the result by 2 will give the actual sensitivity of the sensor. This value changes

very little over temperature (see sensitivity change vs. temperature) and also very little over time. The Sen-

sitivity Tolerance describes the range of Sensitivities of a large population of sensors.

3.1.2 Zero-g level

Describes the actual output signal if there is no acceleration present. A sensor in a steady state on an

horizontal surface will measure 0g in X axis and 0g in Y axis whereas the Z axis will measure +1g. The

output is ideally for a 3.3V powered sensor Vdd/2 = 1650mV. A deviation from ideal 0-g level (1650mV in

this case) is called Zero-g offset. Offset of precise MEMS sensors is to some extend a result of stress to

the sensor and therefore the offset can slightly change after mounting the sensor onto a printed circuit

board or exposing it to extensive mechanical stress. Offset changes little over temperature - see "Zero-g

Level Change vs. Temperature" - the Zero-g level of an individual sensor is very stable over lifetime. The

Zero-g level tolerance describes the range of zero-g levels of a population of sensors.

3.1.3 Self Test

Self Test allows to test the mechanical and electric part of the sensor, allowing the seismic mass to be moved

by means of an electrostatic test-force. The Self Test function is off when the ST pin is connected to GND. When

the ST pin is tied at Vdd an actuation force is applied to the sensor, simulating a definite input acceleration. In

this case the sensor outputs will exhibit a voltage change in their DC levels which is related to the selected full

scale and depending on the Supply Voltage through the device sensitivity. When ST is activated, the device

output level is given by the algebraic sum of the signals produced by the acceleration acting on the sensor and

by the electrostatic test-force. If the output signals change within the amplitude specified inside Table 3, than

the sensor is working properly and the parameters of the interface chip are within the defined specification.

3.1.4 Output impedance

Describes the resistor inside the output stage of each channel. This resistor is part of a filter consisting of

an external capacitor of at least 320pF and the internal resistor. Due to the high resistor level only small,

inexpensive external capacitors are needed to generate low corner frequencies. When interfacing with an

ADC it is important to use high input impedance input circuitries to avoid measurement errors. Note that

the minimum load capacitance forms a corner frequency beyond the resonance frequency of the sensor.

For a flat frequency response a corner frequency well below the resonance frequency is recommended.

In general the smallest possible bandwidth for an particular application should be chosen to get the best

results.