LIS244ALTR Datasheet LIS244AL, LIS244ALTR | P7-P9

LIS244AL Mechanical and electrical specifications

7/15

2.3 Absolute maximum ratings

Stresses above those listed as “absolute maximum ratings” may cause permanent damage

to the device. This is a stress rating only and functional operation of the device under these

conditions is not implied. Exposure to maximum rating conditions for extended periods may

affect device reliability.

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. The

output is ideally for a 3.0V powered sensor Vdd/2 = 1500mV. A deviation from ideal 0-g level

(1500mV 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.

Table 5. Absolute maximum ratings

Symbol Ratings Maximum value Unit

Vdd Supply voltage -0.3 to 6 V

Vin Input voltage on any control pin (ST) -0.3 to Vdd +0.3 V

POW

Acceleration (any axis, powered, Vdd=3.0V)

3000g for 0.5 ms

10000g for 0.1 ms

UNP

Acceleration (any axis, not powered)

3000g for 0.5 ms

10000g for 0.1 ms

STG

Storage temperature range -40 to +125 °C

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

Obsolete Product(s) - Obsolete Product(s)

Mechanical and electrical specifications LIS244AL

8/15

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 , than 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 2.5nF 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.

Obsolete Product(s) - Obsolete Product(s)

LIS244AL Functionality

9/15

3 Functionality

The LIS244AL is an ultra compact low-power, analog output two-axis linear accelerometer

packaged in a LGA package. The complete device includes a sensing element and an IC

interface able to take the information from the sensing element and to provide an analog

signal to the external world.

3.1 Sensing element

A proprietary process is used to create a surface micro-machined accelerometer. The

technology allows to carry out suspended silicon structures which are attached to the

substrate in a few points called anchors and are free to move in the direction of the sensed

acceleration. To be compatible with the traditional packaging techniques a cap is placed on

top of the sensing element to avoid blocking the moving parts during the moulding phase of

the plastic encapsulation.

When an acceleration is applied to the sensor the proof mass displaces from its nominal

position, causing an imbalance in the capacitive half-bridge. This imbalance is measured

using charge integration in response to a voltage pulse applied to the sense capacitor.

At steady state the nominal value of the capacitors are few pF and when an acceleration is

applied the maximum variation of the capacitive load is in pF range.

3.2 IC Interface

The complete signal processing uses a fully differential structure, while the final stage

converts the differential signal into a single-ended one to be compatible with the external

world.

The first stage is a low-noise capacitive amplifier that implements a Correlated Double

Sampling (CDS) at its output to cancel the offset and the 1/f noise. The produced signal is

then sent to two different S&Hs, one for each channel, and made available to the outside.

All the analog parameters (output offset voltage and sensitivity) are ratiometric to the

voltage supply. Increasing or decreasing the voltage supply, the sensitivity and the offset will

increase or decrease linearly. The feature provides the cancellation of the error related to

the voltage supply along an analog to digital conversion chain.

3.3 Factory calibration

The IC interface is factory calibrated for sensitivity (So) and Zero-g level (Voff).

The trimming values are stored inside the device by a non volatile structure. Any time the

device is turned on, the trimming parameters are downloaded into the registers to be

employed during the normal operation. This allows the user to employ the device without

further calibration.

Obsolete Product(s) - Obsolete Product(s)

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15

LIS244ALTR

Mfr. #:

Buy LIS244ALTR

Manufacturer:

STMicroelectronics

Description:

ACCELEROMETER 2-6G ANALOG 16LGA

Lifecycle:

New from this manufacturer.

Delivery:

DHL FedEx Ups TNT EMS

Payment:

T/T Paypal Visa MoneyGram Western Union

LIS244ALTR

LIS244ALTR

Products related to this Datasheet