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) LGA 16 (3x3x1.0mm) 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 Applications ■ Mobile terminals ■ Gaming and virtual reality input devices ■ Antitheft systems and Inertial Navigation ■ Appliance and robotics Description The LIS331AL is the smallest consumer lowpower 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. 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. The sensing element, capable of detecting the acceleration, is manufactured using a dedicated Table 1. Note: Device summary Order code Temp range, ° C Package Packing LIS331AL -40°C to +85°C LGA-16 Tray LIS331ALTR -40°C to +85°C LGA-16 Tape & Reel Tape & Reel parts are compliant to International Standard EIA-481. September 2007 Rev 1 1/16 www.st.com 16 Contents LIS331AL Contents 1 2 3 4 Block diagram & pins description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 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 Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.1 Sensing element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2 IC Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.3 Factory calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Application hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.1 Soldering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2 Output Response vs. Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5 Package Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2/16 LIS331AL List of figures List of figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 LIS331AL Electrical connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Output Response vs. Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 LGA 16: Mechanical data & package dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3/16 List of tables LIS331AL List of tables Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. 4/16 Device summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Mechanical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Filter capacitor selection, Cload (x,y,z) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 LIS331AL Block diagram & pins description 1 Block diagram & pins description 1.1 Block diagram Figure 1. Block diagram X+ CHARGE AMPLIFIER Y+ Z+ a MUX Routx Voutx Routy Vouty Routz Voutz S/H DEMUX S/H ZYX- S/H Pd TRIMMING SELF TEST REFERENCE CLOCK CIRCUIT ST 1.2 Pin description Figure 2. Pin connection 13 Y X Z Direction of the detectable accelerations 1 Voutx NC Vouty NC Voutz res res NC ST PD 9 5 GND NC NC (Top view) Vdd res NC 1 (Bottom view) 5/16 Block diagram & pins description Table 2. 6/16 LIS331AL 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 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 Power Down (Logic 0: normal mode; Logic 1: Power-Down mode) LIS331AL Mechanical and electrical specifications 2 Mechanical and electrical specifications 2.1 Mechanical characteristics. Table 3. Mechanical characteristics(1) (2) Symbol Parameter Ar Acceleration range(4) So Sensitivity(5) SoDr Sensitivity change vs temperature Voff Zero-g level(5) OffDr NL Test condition Typ.(3) Min. Max. Unit ±2.0 0.145*Vdd 5% 0.145*Vdd g 0.145Vdd+ 5% V/g ±0.01 Delta from +25°C Vdd/2-6% Vdd/2 %/°C Vdd/2+6% V Zero-g level change Vs Delta from +25°C Temperature 0.5 mg/°C Non linearity(6) ±0.5 % FS ±2 % 300 µg/ Hz +150 mV +150 mV +150 mV CrossAx Cross-axis Best fit straight line (7) An Acceleration noise density Vt X axis Self test output voltage Y axis change(8) Z axis Fres Sensing element resonant frequency(9) Top Operating temperature range Wh Product weight X,Y,Z axis 2.0 kHz -40 +85 0.030 °C gram 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 3. Typical specifications are not guaranteed 4. Guaranteed by wafer level test and measurement of initial offset and sensitivity 5. Zero-g level and sensitivity are essentially ratiometric to supply voltage at the calibration level ±8% 6. Guaranteed by design 7. Contribution to the measuring output of an inclination/acceleration along any perpendicular axis 8. “Self test output voltage change” is defined as Vout(Vst=Logic1)-Vout(Vst=Logic0) 9. Minimum resonance frequency Fres=2.0kHz. Sensor bandwidth=1/(2*π*32kΩ*Cload) 7/16 Mechanical and electrical specifications 2.2 Electrical characteristics Table 4. Electrical characteristics (1) (2) Symbol Parameter Test condition LIS331AL Min. Typ(3). Max. Unit 3.0 3.3 3.6 V Vdd Supply voltage Idd Supply current Mean value PD pin connected to GND 0.65 mA Supply current in power down mode PD pin connected to Vdd 1 µA IddPdn Vst Logic 0 level 0 0.8 V Logic 1 level 2.0 Vdd V Self test input Rout Output impedance of Voutx, Vouty, Voutz Ton Turn-On time at exit from power down mode Cload in µF 32 kΩ 160*Cload+0.3 ms 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 3. Typical specifications are not guaranteed Note: 8/16 Minimum resonance frequency Fres=2.0kHz. Device bandwidth=1/(2*π*32kΩ*Cload) LIS331AL 2.3 Mechanical and electrical specifications 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. Absolute maximum ratings Symbol Ratings Vdd Supply voltage Vin Input voltage on any control pin (ST,PD) Maximum value Unit -0.3 to 6 V -0.3 to Vdd +0.3 V 3000g for 0.5 ms APOW Acceleration (any axis, powered, Vdd=3.3V) AUNP Acceleration (any axis, not powered) 10000g for 0.1 ms 3000g for 0.5 ms ESD TSTG 10000g for 0.1 ms Electrostatic discharge protection Storage temperature range 4.0 (HBM) kV 1.5 (CDM) kV 400 (MM) V -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 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 9/16 Mechanical and electrical specifications LIS331AL 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, 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. 10/16 LIS331AL 3 Functionality 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. 11/16 Application hints 4 LIS331AL Application hints Figure 3. LIS331AL electrical connection Vdd GND GND 100nF 10µF 1 Pin 1 indicator Y X 16 15 14 Cload x 13 1 2 3 ST PD LIS331AL (top view) 12 Cload y 11 4 10 5 9 7 6 Vout x Optional Z Vout y Cload z Vout z (Top view) Direction of the detectable accelerations 8 GND Digital signals 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: 1 f t = -----------------------------------------------------------------------2π ⋅ R out ⋅ C load ( x, y, z ) 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: 5µF f t = --------------------------------------- [ Hz ] C load ( x, y, z ) 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. 12/16 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 LIS331AL Application hints Table 6. 4.1 Filter capacitor selection, Cload (x,y,z) Cut-off frequency Capacitor value 100 Hz 50nF 200 Hz 25nF 500 Hz 10nF 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=1.65V (0g) Y=2.13V (+1g) Z=1.65V (0g) Bottom X=2.13V (+1g) Y=1.65V (0g) Z=1.65V (0g) TOP VIEW X=1.65V (0g) Y=1.17V (-1g) Z=1.65V (0g) X=1.17V (-1g) Y=1.65V (0g) Z=1.65V (0g) Top Top X=1.65V (0g) Y=1.65V (0g) Z=2.13V (+1g) X=1.65V (0g) Y=1.65V (0g) Bottom Z=1.17V (-1g) Earth’s Surface Figure 4 refers to LIS331AL powered at 3.3V. 13/16 Package information 5 LIS331AL 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. MIN. A1 mm inch TYP. MAX. MIN. TYP. 1 A2 0.031 0.20 0.008 D1 2.850 3 3.150 0.111 0.117 0.123 E1 2.850 3 3.150 0.111 0.117 0.123 L1 Outline and mechanical data 0.039 0.80 A3 MAX. 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 M 0.10 0.0039 P1 0.875 0.034 P2 1.275 0.05 k 0.05 0.0019 LGA 16 (3x3x1.0mm) 7983231E 14/16 LIS331AL 6 Revision history Revision history Table 7. Document revision history Date Revision 28-Sep-2007 1 Changes Initial release. 15/16 LIS331AL Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. 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