LIS344AL

Mechanical and electrical specifications

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2.4

Terminology

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 Sensitivity tolerance describes the range of Sensitivities of a large population of

sensors.

Zero-g level describes the actual output signal if there is no acceleration present. A sensor

in a steady state on a 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 3.0V powered sensor Vdd/2 = 1500

mV. A deviation from ideal 0-g level (1500 mV 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.

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 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, then the sensor is working properly and the parameters of the interface chip are

within the defined specification.

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 2.5 nF and the internal

resistor. Due to the 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 close to the resonance frequency of the sensor. In

general the smallest possible bandwidth for a particular application should be chosen to get

the best results.

This is a Mechanical Shock sensitive device, improper handling can cause permanent

damages to the part

This is an ESD sensitive device, improper handling can cause permanent damages to

the part