LIS244AL
MEMS motion sensor: 2-axis - 2g ultracompact linear accelerometer
Features
Single voltage supply operation
2g full-scale
Output voltage, offset and sensitivity are ratiometric to the supply voltage Factory trimmed device sensitivity and offset Embedded self test ECOPACK lead-free compliant High shock survivability (10000g) The LIS244AL is capable of measuring accelerations over a maximum bandwidth of 2.0kHz. The device bandwidth may be reduced by using external capacitances. A self-test capability allows the user to check the functioning of the system. The LIS244AL is available in Land Grid Array package (LGA) and it is guarantee to operate over an extended temperature range of -40C to +85C. The LIS244AL belongs to a family of products suitable for a variety of applications: Mobile terminals Gaming and Virtual Reality input devices Antitheft systems and Inertial Navigation Appliance and Robotics.
LGA 16 (4x4x1.5mm)
Description
The LIS244AL is an ultra compact consumer lowpower two-axis linear accelerometer that 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. The sensing element, capable of detecting the acceleration, is manufactured using a dedicated process developed by ST to produce inertial sensors and actuators in silicon. The IC interface is manufactured using a CMOS process that allows high level of integration to design a dedicated circuit which is trimmed to better match the sensing element characteristics.
Table 1.
Device summary
Temp range, C -40C to +85C -40C to +85C Package LGA-16 LGA-16 Packing Tray Tape & Reel
Order codes LIS244AL LIS244ALTR
Note:
Tape & Reel parts are compliant to International Standard EIA-481.
June 2007
Rev 1
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Contents
LIS244AL
Contents
1 Block diagram & pins description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 1.2 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Pin Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2
Mechanical and electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 2.2 2.3 2.4 Mechanical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3
Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1 3.2 3.3 Sensing element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 IC Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Factor y calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4
Application hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1 4.2 Soldering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Output Response vs. orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5 6
Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
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LIS244AL
Block diagram & pins description
1
1.1
Block diagram & pins description
Block diagram
Figure 1. Block diagram
X+ Y+
CHARGE AMPLIFIER S/H
Routx
Voutx
a
YX-
MUX
DEMUX Routy S/H
Vouty
SELF TEST
REFERENCE
TRIMMING CIRCUIT
CLOCK
St
1.2
Pin Description
Figure 2. Pin Connection
NC
Vdd
NC res
1
12
1
VoutX NC
X Y
NC ST GND NC
4
Vouty NC
8
NC
GND
GND
GND
(TOP VIEW) DIRECTION OF THE DETECTABLE ACCELERATIONS
(BOTTOM VIEW)
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Block diagram & pins description
LIS244AL
Table 2.
Pin # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Pin description
Pin name NC ST GND NC GND GND GND NC NC Vouty NC Voutx NC Vdd Res NC Function Not to be connected Self test (logic 0: normal mode; logic 1: self-test mode) 0V supply Not to be connected 0V supply 0V supply 0V supply Not to be connected Not to be connected Output voltage Y channel Not to be connected Output voltage X channel Not to be connected Power supply Connect to Vdd Not to be connected
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LIS244AL
Mechanical and electrical specifications
2
2.1
Mechanical and electrical specifications
Mechanical characteristics
(Temperature range -40C to +85C). All the parameters are specified @ Vdd =3.0V, T = 25C unless otherwise noted
Table 3.
Symbol Ar So SoDr Voff OffDr NL
Mechanical characteristics(1)
Parameter Acceleration range(3) Sensitivity(5) Sensitivity change vs temperature Zero-g level(4) Delta from +25C T = 25C Vdd/2-15% 0.140*Vdd 10% Test condition Min. Typ.(2) 2 0.140*Vdd 0.01 Vdd/2 1 0.5 2 Vdd=3.0V 220 Vdd/2+15% 0.140*Vdd+ 10% Max. Unit g V/g %/C V mg/C % FS % g/ H z
Zero-g level change vs Delta from +25C temperature Non linearity(5)
(6)
Best fit straight line
CrossAx Cross-axis An
Acceleration noise density
Vt
T = 25C Vdd=3.0V Self test output voltage X axis change(7), T = 25C Vdd=3.0V Y axis
105
mV
105
mV
Fres Top Wh
Sensing element resonant frequency(8) Operating temperature range Product weight
X,Yaxis
4.0 -40 0.040 +85
kHz C gram
1. The product is factory calibrated at 3.0V. The operational power supply range is from 2.4V to 3.6V. Voff, So and Vt parameters will vary with supply voltage 2. Typical specifications are not guaranteed 3. Guaranteed by wafer level test and measurement of initial offset and sensitivity 4. Zero-g level and sensitivity are essentially ratiometric to supply voltage at the calibration level 8% 5. Guaranteed by design 6. Contribution to the measuring output of an inclination/acceleration along any perpendicular axis 7. "Self test output voltage change" is defined as Vout(Vst=Logic1)-Vout(Vst=Logic0) 8. Minimum resonance frequency Fres=4.0kHz. Sensor bandwidth=1/(2**32k*Cload)
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Mechanical and electrical specifications
LIS244AL
2.2
Electrical characteristics
(Temperature range -40C to +85C) All the parameters are specified @ Vdd =3.0V, T=25C unless otherwise noted Table 4.
Symbol Vdd Idd Vst
Electrical characteristics(1)
Parameter Supply voltage Supply current Logic 0 level Self test input Logic 1 level 2.0 32 Vdd V k Output impedance of Voutx, Vouty 0 Test condition Min. 2.4 Typ.(2) 3.0 0.65 0.8 Max. 3.6 Unit V mA V
Rout
1. The product is factory calibrated at 3.0V 2. Typical specifications are not guaranteed
Note:
Minimum resonance frequency Fres=4.0kHz. Device bandwidth=1/(2**32k*Cload)
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LIS244AL
Mechanical and electrical specifications
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. Table 5.
Symbol Vdd Vin APOW Supply voltage Input voltage on any control pin (ST) Acceleration (any axis, powered, Vdd=3.0V) 10000g for 0.1 ms 3000g for 0.5 ms AUNP TSTG Acceleration (any axis, not powered) 10000g for 0.1 ms Storage temperature range -40 to +125 C
Absolute maximum ratings
Ratings Maximum value -0.3 to 6 -0.3 to Vdd +0.3 3000g for 0.5 ms Unit V V
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
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.
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Mechanical and electrical specifications
LIS244AL
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.
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LIS244AL
Functionality
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.
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Application hints
LIS244AL
4
Application hints
Figure 3. LIS244AL Electrical connection
Vdd GND 100nF GND 10F
1 16 1
ST
Pin 1 indicator
15
14
13 12
Cload x
Optional Vout x
2 3 4 5
LIS244AL
(top view)
11 10 9
X
Optional Vout y
Y
Cload y
6
7
8
GND
(TOP VIEW) DIRECTION OF THE DETECTABLE ACCELERATIONS
Digital signals
Power supply decoupling capacitors (100nF ceramic or polyester + 10F Aluminum) should be placed as near as possible to the device (common design practice). The LIS244AL allows to band limit Voutx, Vouty through the use of external capacitors. The recommended frequency range spans from DC up to 2.0kHz. In particular, capacitors are added at output Voutx, Vouty pins to implement low-pass filtering for antialiasing and noise reduction. The equation for the cut-off frequency (ft) of the external filters is in this case: Equation 1
1 f t = ---------------------------------------------------------------2 R o u t C l o a d ( x, y )
Taking into account that the internal filtering resistor (Rout) has a nominal value equal to 32k the equation for the external filter cut-off frequency may be simplified as follows: , Equation 2
5 F f t = ------------------------- [ H z ] C l o a d x, y
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LIS244AL
Application hints The tolerance of the internal resistor can vary typically of 20% within its nominal value of 32k; thus the cut-off frequency will vary accordingly. A minimum capacitance of 2.5nF for Cload(x, y) is required. Table 6. Filter Capacitor Selection, Cload (x,y),
Cut-off frequency 1 Hz 10 Hz 20 Hz 50 Hz 100 Hz 200 Hz 500 Hz Capacitor value 5 F 0.5F 250nF 100nF 50nF 25nF 10nF
4.1
Soldering information
The LGA package is compliant with the ECOPACK, RoHs and "Green" standard. Pin1 indicator is electrically connected to pin 1. Leave pin 1 indicator unconnected during soldering.
4.2
Output Response vs. orientation
Figure 4. Output response vs. orientation
X=1.50V (0g) Y=1.83V (+1g)
Top Bottom
X=1.83V (+1g) Y=1.50V (0g) TOP VIEW X=1.17V (-1g) Y=1.50V (0g)
X=1.50V (0g) Y=1.50V (0g)
Top Bottom
X=1.50V (0g) Y=1.50V (0g)
X=1.50V (0g) Y=1.17V (-1g)
Earth's Surface
Figure 4 refers to LIS244AL powered at 3.0V.
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Package information
LIS244AL
5
Package information
In order to meet environmental requirements, ST offers these devices in ECOPACK packages. These packages have a Lead-free second level interconnect. The category of second Level Interconnect is marked on the package and on the inner box label, in compliance with JEDEC Standard JESD97. The maximum ratings related to soldering conditions are also marked on the inner box label. ECOPACK is an ST trademark. ECOPACK specifications are available at: www.st.com.
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LIS244AL Figure 5. LGA 16: mechanical data & package dimensions
Package information
Dimensions Ref.
A1 A2 A3 D1 E1 L L1 N N1 T1 T2 P1 P2 R S k 0.160 3.850 3.850 0.20 4.0 4.0 0.65 1.95 0.98 1.90 0.40 0.30 1.750 1.525 0.30 0.10 0.05
mm Min. Typ.
1
inch Max. Min.
1.60 1.33 0.24 4.150 4.150 0.006 0.152 0.152 0.008 0.157 0.157 0.026 0.077 0.039 0.075 0.016 0.012 0.069 0.060 0.012 0.004 0.0019
Typ.
0.039
Max.
0.063 0.052 0.009 0.163 0.163
Outline and mechanical data
LGA 16 (4x4x1.5mm)
7974136
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Revision history
LIS244AL
6
Revision history
Table 7.
Date 29-Jun-2007
Document revision history
Revision 1 Initial release Changes
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LIS244AL
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