September 2007 Rev 1 1/16
16
LIS331AL
MEMS inertial sensor:
3-axis - ±2g analog output “nano” accelerometer
Features
■Single voltage supply operation
■±2.0g 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)
Applications
■Mobile terminals
■Gaming and virtual reality input devices
■Antitheft systems and Inertial Navigation
■Appliance and robotics
Description
The LIS331AL is the smallest consumer low-
power three-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.
The LIS331AL 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 LIS331AL is available in Land Grid Array
package (LGA) and it is guaranteed to operate
over an extended temperature range of -40°C to
+85°C.
Note: Tape & Reel parts are compliant to International Standard EIA-481.
LGA 16
(3x3x1.0mm)
Table 1. Device summary
Order code Temp range, °CPackage Packing
LIS331AL -40°C to +85°C LGA-16 Tray
LIS331ALTR -40°C to +85°C LGA-16 Tape & Reel
www.st.com
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Contents LIS331AL
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Contents
1 Block diagram & pins description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Mechanical and electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Mechanical characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1 Sensing element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2 IC Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3 Factory calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4 Application hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1 Soldering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.2 Output Response vs. Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5 Package Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
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LIS331AL List of figures
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List of figures
Figure 1. Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Figure 2. Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Figure 3. LIS331AL Electrical connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Figure 4. Output Response vs. Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 5. LGA 16: Mechanical data & package dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
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List of tables LIS331AL
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List of tables
Table 1. Device summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Table 2. Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Table 3. Mechanical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Table 4. Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Table 5. Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Table 6. Filter capacitor selection, Cload (x,y,z) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Table 7. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
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LIS331AL Block diagram & pins description
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1 Block diagram & pins description
1.1 Block diagram
Figure 1. Block diagram
1.2 Pin description
Figure 2. Pin connection
S/H
S/H
Routx
Routz
REFERENCE
TRIMMING CLOCK
S/H
Routy
CHARGE
AMPLIFIER
MUX DEMUX
Voutx
Voutz
Vouty
Y+
Z+
Y-
Z-
X+
X-
a
SELF TEST
ST
Pd
CIRCUIT
(Bottom view)
res
res
NC
ST
NC
Vouty
NC
Voutz
NC
GND
NC
NC
res
Vdd
1
5
9
13
(Top view)
Direction of the detectable
Y
1
X
Z
PD
Voutx
accelerations
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Block diagram & pins description LIS331AL
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Table 2. Pin description
Pin # Pin name Function
1 res Connect to Vdd
2 res Connect to Vdd
3 NC Not Connected
4 ST Self Test (Logic 0: normal mode; Logic 1: Self-Test mode)
5 PD Power Down (Logic 0: normal mode; Logic 1: Power-Down mode)
6 GND 0V supply
7 NC Not connected
8 NC Not connected
9 Voutz Output voltage Z channel
10 NC Not connected
11 Vouty Output voltage Y channel
12 NC Not connected
13 Voutx Output voltage X channel
14 NC Not connected
15 res Connect to Vdd
16 Vdd Power supply
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LIS331AL Mechanical and electrical specifications
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2 Mechanical and electrical specifications
2.1 Mechanical characteristics.
Table 3. Mechanical characteristics(1) (2)
1. The product is factory calibrated at 3.3V. The operational power supply range is from 3.0V to 3.6V. Voff, So and Vt
parameters will vary with supply voltage.
2. Temperature range -40°C to +85°C. All the parameters are specified @ Vdd =3.3V, T = 25°C unless otherwise noted
Symbol Parameter Test condition Min. Typ.(3)
3. Typical specifications are not guaranteed
Max. Unit
Ar Acceleration range(4)
4. Guaranteed by wafer level test and measurement of initial offset and sensitivity
±2.0 g
So Sensitivity(5) 0.145*Vdd -
5% 0.145*Vdd 0.145Vdd+
5% V/g
SoDr Sensitivity change vs
temperature Delta from +25°C ±0.01 %/°C
Voff Zero-g level(5)
5. Zero-g level and sensitivity are essentially ratiometric to supply voltage at the calibration level ±8%
Vdd/2-6% Vdd/2 Vdd/2+6% V
OffDr Zero-g level change Vs
Temperature Delta from +25°C 0.5 mg/°C
NL Non linearity(6)
6. Guaranteed by design
Best fit straight line ±0.5 % FS
CrossAx Cross-axis(7)
7. Contribution to the measuring output of an inclination/acceleration along any perpendicular axis
±2%
An Acceleration noise
density 300 µg/
Vt Self test output voltage
change(8)
8. “Self test output voltage change” is defined as Vout(Vst=Logic1)-Vout(Vst=Logic0)
X axis +150 mV
Y axis +150 mV
Z axis +150 mV
Fres Sensing element
resonant frequency(9)
9. Minimum resonance frequency Fres=2.0kHz. Sensor bandwidth=1/(2*π*32kΩ*Cload)
X,Y,Z axis 2.0 kHz
To p Operating temperature
range -40 +85 °C
Wh Product weight 0.030 gram
Hz
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Mechanical and electrical specifications LIS331AL
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2.2 Electrical characteristics
Note: Minimum resonance frequency Fres=2.0kHz. Device bandwidth=1/(2*
π
*32k
Ω
*Cload)
Table 4. Electrical characteristics (1) (2)
1. The product is factory calibrated at 3.3V
2. Temperature range -40°C to +85°C. All the parameters are specified @ Vdd =3.3V, T=25°C unless otherwise noted
Symbol Parameter Test condition Min. Typ(3).
3. Typical specifications are not guaranteed
Max. Unit
Vdd Supply voltage 3.0 3.3 3.6 V
Idd Supply current Mean value
PD pin connected to GND 0.65 mA
IddPdn Supply current in
power down mode PD pin connected to Vdd 1 µA
Vst Self test input Logic 0 level 0 0.8 V
Logic 1 level 2.0 Vdd V
Rout Output impedance of
Voutx, Vouty, Voutz 32 kΩ
To n
Turn-On time at exit
from power down
mode
Cload in µF 160*Cload+0.3 ms
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LIS331AL Mechanical and electrical specifications
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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 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
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,PD) -0.3 to Vdd +0.3 V
APOW Acceleration (any axis, powered, Vdd=3.3V) 3000g for 0.5 ms
10000g for 0.1 ms
AUNP Acceleration (any axis, not powered) 3000g for 0.5 ms
10000g for 0.1 ms
ESD Electrostatic discharge protection
4.0 (HBM) kV
1.5 (CDM) kV
400 (MM) V
TSTG 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
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Mechanical and electrical specifications LIS331AL
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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
Ta bl e 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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LIS331AL Functionality
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3 Functionality
The LIS331AL is a nano low-power, analog output three-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 fF 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 three 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 LIS331AL
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4 Application hints
Figure 3. LIS331AL electrical connection
Power supply decoupling capacitors (100 nF ceramic or polyester + 10 µF aluminum) should
be placed as near as possible to the device (common design practice).
The LIS331AL allows to band limit Voutx, Vouty and Voutz through the use of external
capacitors. The recommended frequency range spans from DC up to 2.0 kHz. In particular,
capacitors are added at output Voutx, Vouty, Voutz 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:
Taking into account that the internal filtering resistor (Rout) has a nominal value equal to 32
kΩ, the equation for the external filter cut-off frequency may be simplified as follows:
The tolerance of the internal resistor can vary typically of ±20% within its nominal value of 32
kΩ; thus the cut-off frequency will vary accordingly. A minimum capacitance of 2.5 nF for
Cload(x, y, z) is required.
Table 6. Filter capacitor selection, Cload (x,y,z)
Cut-off frequency Capacitor value
1 Hz 5 µF
10 Hz 0.5µF
20 Hz 250nF
50 Hz 100nF
Pin 1 indicator
Vdd
GND
GND
100nF 10
µ
F
GND
(Top view)
Direction of the
detectable
accelerations
Y
1
X
Z
Digital signals
LIS331AL
(top view)
ST
1
5
13
Cload y
Vout x
Cload x
Optional
Vout y
Cload z
Vout z
2
3
4
12
11
10
9
16 15 14
678
PD
ft
1
2πRout Cload xyz,,()⋅⋅
-------------------------------------------------------------------------=
ft
5µF
Cload xyz,,()
---------------------------------------Hz[]=
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LIS331AL Application hints
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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
Figure 4 refers to LIS331AL powered at 3.3V.
100 Hz 50nF
200 Hz 25nF
500 Hz 10nF
Table 6. Filter capacitor selection, Cload (x,y,z)
Cut-off frequency Capacitor value
Earth’s Surface
X=1.65V (0g)
Y=1.65V (0g)
Z=1.17V (-1g)
X=1.65V (0g)
Y=1.65V (0g)
Z=2.13V (+1g)
TOP VIEW
X=1.65V (0g)
Y=2.13V (+1g)
X=1.65V (0g)
Y=1.17V (-1g)
X=1.17V (-1g)
Y=1.65V (0g)
X=2.13V (+1g)
Y=1.65V (0g)
Z=1.65V (0g)
Z=1.65V (0g)
Z=1.65V (0g)
Z=1.65V (0g)
Top
Bottom
To p
Bottom
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Package information LIS331AL
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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.
Figure 5. LGA 16: mechanical data & package dimensions
DIMENSIONS
REF.
mm inch
MIN. TYP. MAX. MIN. TYP. MAX.
A1 1 0.039
A2 0.800.031
A30.20 0.008
D1 2.850 33.150 0.111 0.117 0.123
E1 2.850 33.150 0.111 0.117 0.123
L1 1 0.039
L2 2 0.078
N1 0.50 0.019
N2 1 0.039
T1 0.350 0.013
T2 0.250 0.001
M0.10 0.0039
P1 0.875 0.034
P2 1.275 0.05
k0.05 0.0019
LGA 16 (3x3x1.0mm)
Outline and
7983231E
mechanical data
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LIS331AL Revision history
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6 Revision history
Table 7. Document revision history
Date Revision Changes
28-Sep-2007 1 Initial release.
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