LIS344ALH STMICROELECTRONICS | Alldatasheet
Document overview
- Manufacturer or author: pROVIDED bY alldatasheet.com(free datasheet download site)
- PDF pages: 16
Technical content
Features
■ 2.4 V to 3.6 V single supply operation ■ ±2 g / ±6 g user selectable full-scale ■ Low power consumption ■ Output voltage, offset and sensitivity are ratiometric to the supply voltage ■ Factory trimmed device sensitivity and offset ■ Embedded self test ■ RoHS/ECOPACK® compliant ■ High shock survivability ( 10000 g )
Description
The LIS344ALH is an ultra compact 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 an ST proprietary CMOS process with high level of integration. The dedicated circuit is trimmed to better match the sensing element characteristics. The LIS344ALH has a dynamically user selectable full-scale of ±2 g / ±6 g and it is capable of measuring accelerations over a maximum bandwidth of 1.8 kHz for all axes. The device bandwidth may be reduced by using external capacitances. The self-test capability allows the user to check the functioning of the system. The LIS344ALH is available in Land Grid Array package (LGA) manufactured by ST. It is guaranteed to operate over an extended temperature range of -40 °C to +85 °C. The LIS344ALH 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 (4x4x1.5 mm) Table 1. Device summary
Table 6. Filter capacitor selection, C
1 Block diagram and pin description
1.1 Block diagram
Figure 1. Block diagram
1.2 Pin description
Figure 2. Pin connection
Table 2. Pin description
1 FS Full scale selection (L ogic 0: ±2g Full-scale; Logic 1: ±6g Full-scale)
2 ST Self test (Logic 0: normal mode; Logic 1: Self-test mode)
3 NC Internally not connected
4 Res Leave unconnected or connect to Vdd
5 PD Power Down (Logic 0: normal mode; Logic 1: Power-Down mode)
6 NC Internally not connected
7 GND 0 V supply
8 VoutZ Output voltage Z channel
9 NC Internally not connected
10 VoutY Output voltage Y channel
11 NC Internally not connected
12 VoutX Output voltage X channel
13 NC Internally not connected
14 Vdd Power supply
15 Res Connect to Vdd
16 NC Internally not connected
2 Mechanical and electrical specifications
2.1 Mechanical characteristics
Table 3. Mechanical characteristics @ Vdd =3.3 V, T = 25 °C unless otherwise noted (1) parameters will vary with supply voltage.
- Typical specificat ions are not guaranteed.
- Guaranteed by wafer level test and measurement of initial offset and sensitivity.
- Zero-g level and sensitivity are e ssentially ratiometric to supply voltage at the calibration level ±8%.
- Contribution to the measuring output of an in clination/acceleration along any perpendicular axis.
- “Self test output voltage change” is defined as Vout
(Vst=Logic1)-Vout(Vst=Logic0).
- “Self test output voltage change” va ries cubically with supply voltage.
- When full-scale is set to ±6 g, “Self test output volt age change” is one third of the specified value at ±2 g.
- Minimum resonance frequency Fres=1.8 kHz. Sensor bandwidth=1/(2*π*110kΩ*Cload), with Cload>1 nF.
2.2 Electrical characteristics
Table 4. Electrical characteristics @ Vdd =3.3 V, T = 25 °C unless otherwise noted (1)
- The product is factory calibrated at 3.3 V.
- Typical specificat ions are not guaranteed.
- Minimum resonance frequency Fres=1 .8 kHz. Device bandwidth=1/(2*π*110 kΩ*Cload), with Cload>1 nF.
2.3 Absolute maximum ratings
Table 5. Absolute maximum ratings
Mechanical and electrical specifications LIS344ALH
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 3.3 V powered sensor Vdd/2 = 1650 mV. A deviation from ideal 0-g level (1650 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 related to the selected full-scale and 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 ble 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 1 nF and the internal resistor. Due to the high 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.
3 Functionality
The LIS344ALH is an ultra compact 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 the 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. This 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.
4 Application hints
Figure 3. LIS344ALH electrical connection should be placed as near as possible to the device (common design practice).
110 KΩ, the equation for the external filter cut-off frequency may be simplified as follows:
4.1 Soldering information
The LGA package is compliant with the ECOPACK, RoHs and “Green” standard. It is qualified for soldering heat resistance according to JEDEC J-STD-020C. Leave “Pin 1 Indicator” unconnected during soldering.
4.2 Output response vs orientation
Figure 4. Output response vs orientation Figure 4 shows output voltage values of LIS344ALH, powered at 3.3 V, with full-scale ±2 g. Table 6. Filter capacitor selection, C load (x, y, z),
1 Hz 1500 nF
10 Hz 150 nF
20 Hz 68 nF
50 Hz 30 nF
100 Hz 15 nF
500 Hz 3 nF
5 Package Information
ECOPACK® specifications are available at: www.st.com. Figure 5. LGA 16: mechanical data and package dimensions
6 Revision history
Table 7. Document revision history 15-Jan-2008 1 Initial release.