LIS332AR STMICROELECTRONICS | Alldatasheet
Document overview
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- PDF pages: 14
Technical content
Datasheet sections
- 1 Block diagram and pin description
- 1.1 Pin connections and description
- 2 Mechanical and electrical specifications
- 2.1 Mechanical characteristics
- 2.2 Electrical characteristics
- 3 Absolute maximum ratings
- 4 Terminology
- 4.1 Sensitivity
- 4.2 Zero-g level
- 4.3 Self-test
- 4.4 Output impedance
- 5 Functionality
- 5.1 Sensing element
- 5.2 IC interface
- 5.3 Factory calibration
- 6 Application hints
- 6.1 Soldering information
- 7 Package information
- 8 Revision history
Features
■ Single voltage supply operation ■ ±2 g full-scale ■ High stability over temperature ■ Ratiometric output voltage ■ Power-down mode ■ Embedded self-test ■ 10000 g high shock survivability ■ ECOPACK® RoHS and “Green” compliant (see Section 7)
Applications
■ Tilting applications ■ Free-fall detection ■ Gaming ■ Anti-theft systems ■ Inertial navigation and motion tracking
Description
The LIS332AR is a miniaturized low-power 3-axis linear accelerometer belonging to the “nano” family of ST motion sensors. It includes a sensing element and an IC interface 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 motion sensors and actuators in silicon. The IC interface is manufactured using a CMOS process that allows the design of a dedicated circuit which is trimmed to better match the sensing element characteristics. The LIS332AR has a full-scale of ±2 g, and is capable of measuring accelerations over a maximum bandwidth of 2.0 kHz. The device bandwidth may be reduced by using external capacitors. The self-test capability allows the user to check the functioning of the sensor in the final application. ST is already in the field with several hundred million sensors which have received excellent acceptance from the market in terms of quality, reliability and performance. The LIS332AR is provided in a plastic land grid array (LGA) package. Several years ago ST successfully pioneered the use of this package for accelerometers. Today, ST has the widest manufacturing capability and strongest expertise in the world for production of sensors in plastic LGA packages. LGA-16 (3x3x1.0mm) Table 1. Device summary
1 Block diagram and pin description
Figure 1. Block diagram
1.1 Pin connections and description
Figure 2. Pin connection
Table 2. Pin description
1 NC Internally not connected
3 NC Internally 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 0 V supply
7 NC Internally not connected
8 NC Internally not connected
9 Voutz Output voltage Z channel
10 NC Internally not connected
11 Vouty Output voltage Y channel
12 NC Internally not connected
13 Voutx Output voltage X channel
14 NC Internally not connected
16 Vdd Power supply
2 Mechanical and electrical specifications
2.1 Mechanical characteristics
@ Vdd=3 V, T=25 °C unless otherwise noted(a). device is ratiometric, Voff, So and Vt parameters vary with supply voltage. Table 3. Mechanical characteristics
- Typical specificat ions are not guaranteed
- Guaranteed by wafer level test and measurement of initial offset and sensitivity
- Zero- g level and sensitivity are ratiometric to supply voltage
- Contribution to the measured output of an incl ination/acceleration along any perpendicular axis
- “Self-test output voltage change” is defined as Vout
- “Self-test output voltage change” varies cubically with supply voltage
- Minimum resonance frequency F RES=2.0 kHz. Sensor bandwidth=1/(2*π*32kΩ*CLOAD), with CLOAD>2.5 nF
2.2 Electrical characteristics
@ Vdd=3 V, T=25 °C unless otherwise noted(b). b. The product is factory calibrated at 3 V. Table 4. Electrical characteristics
- Typical specificat ions are not guaranteed
- Minimum resonance frequency F RES=2.0 kHz. Device bandwidth=1/(2*π*32kΩ*CLOAD), with CLOAD>2.5 nF
3 Absolute maximum ratings
Note: Supply voltage on any pin should never exceed 6.0 V. Table 5. Absolute maximum ratings
4 Terminology
4.1 Sensitivity
Sensitivity describes the gain of the sensor and can be determined by applying 1 g acceleration to it. Because the sensor can measure DC accelerations, this can be done easily by pointing the selected axis towards the ground, noting the output value, rotating the sensor 180 degrees (pointing towards the sky) and noting the output value again. By doing so, a ±1 g acceleration is applied to the sensor. Subtracting the larger output value from the smaller one, and dividing the result by 2, produces the actual sensitivity of the sensor. This value changes very little over temperature (see sensitivity change vs. temperature) and over time. The sensitivity tolerance describes the range of sensitivities of a large number of sensors.
4.2 Zero- g level
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 0 g on both the X and Y axes, whereas the Z axis will measure 1 g. Ideally, the output for a 3 V powered sensor is Vdd/2 = 1500 mV. A deviation from the ideal 0 g level (1500 mV, in this case) is called Zero-g offset. Offset is to some extent a result of stress to the MEMS 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” in Table 3: Mechanical characteristics). The Zero-g level of an individual sensor is also very stable over its lifetime. The Zero-g level tolerance describes the range of Zero-g levels of a group of sensors.
4.3 Self-test
Self-test (ST) allows the checking of sensor functionality without moving it. The self-test function is off when the ST pin is connected to GND. When the ST pin is tied to Vdd, an actuation force is applied to the sensor, simulating a definite input acceleration. In this case, the sensor outputs exhibit a voltage change in their DC levels. 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 in Table 3, then the sensor is working properly and the parameters of the interface chip are within the defined specifications.
4.4 Output impedance
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 2.5 nF 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 resonant frequency of the sensor. In general, the smallest possible bandwidth for a particular application should be chosen to obtain the best results.
5 Functionality
The LIS332AR is a 3-axis ultracompact, low-power, analog output accelerometer packaged in an LGA package. The complete device includes a sensing element and an IC interface capable of taking information from the sensing element and providing an analog signal to the external world.
5.1 Sensing element
A proprietary process is used to create a surface micro-machined accelerometer. The technology allows the creation of suspended silicon structures which are attached to the substrate at several points called “anchors” and are free to move in the direction of the sensed acceleration. To be compatible with traditional packaging techniques, a cap is placed on top of the sensing element to prevent blocking of the moving parts during the moulding phase of plastic encapsulation. When an acceleration is applied to the sensor, the proof mass shifts 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 a few pF , and when an acceleration is applied the maximum variation of the capacitive load is in the fF range.
5.2 IC interface
The complete signal processing utilizes a fully differential structure, while the final stage converts the differential signal into a single-ended signal to be compatible with external applications. 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 signal produced 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 increases or decreases linearly. This feature provides for cancellation of the error related to the voltage supply along an analog-to-digital conversion chain.
5.3 Factory calibration
The IC interface is factory-calibrated for sensitivity (So) and Zero-g level (Voff). The trimming values are stored in the device in a non-volatile structure. Any time the device is turned on, the trimming parameters are downloaded to the registers to be employed during normal operation. This allows the user to use the device without further calibration.
6 Application hints
Figure 3. LIS332AR electrical connection be placed as near as possible to the device (common design practice).
6.1 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. Figure 4. Output response vs. orientation Figure 4 refers to the LIS332AR powered at 3 V. Table 6. Filter capacitor selection, C LOAD (x,y,z)
1 Hz 5 µF
20 Hz 250 nF
50 Hz 100 nF
100 Hz 50 nF
200 Hz 25 nF
500 Hz 10 nF
7 Package information
Figure 5. LGA-16: mechanical data and package dimensions
8 Revision history
Table 7. Document revision history 02-Feb-2010 1 Initial release.