LIS244AL STMICROELECTRONICS | Alldatasheet
Document overview
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- PDF pages: 15
Technical content
Datasheet sections
- 1 Block diagram & pins description
- 1.1 Block diagram
- 1.2 Pin Description
- 2 Mechanical and electrical specifications
- 2.1 Mechanical characteristics
- 2.2 Electrical characteristics
- 2.3 Absolute maximum ratings
- 2.4 Terminology
- 3 Functionality
- 3.1 Sensing element
- 3.2 IC Interface
- 3.3 Factory calibration
- 4 Application hints
- 4.1 Soldering information
- 5 Package information
- 6 Revision history
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)
Description
The LIS244AL is an ultra compact consumer low- power 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. 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 -40°C to +85°C. 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. Note: Tape & Reel parts are compliant to International Standard EIA-481. LGA 16 (4x4x1.5mm) Table 1. Device summary
1 Block diagram & pins description
1.1 Block diagram
Figure 1. Block diagram
1.2 Pin Description
Figure 2. Pin Connection
Table 2. Pin description
1 NC Not to be connected
2 ST Self test (logic 0: normal mode; logic 1: self-test mode)
3 GND 0V supply
4 NC Not to be connected
5 GND 0V supply
6 GND 0V supply
7 GND 0V supply
8 NC Not to be connected
9 NC Not to be connected
10 Vouty Output voltage Y channel
11 NC Not to be connected
12 Voutx Output voltage X channel
13 NC Not to be connected
14 Vdd Power supply
15 Res Connect to Vdd
16 NC Not to be connected
2 Mechanical and electrical specifications
2.1 Mechanical characteristics
Table 3. Mechanical characteristics (1)
- Typical specificat ions are not guaranteed
- Guaranteed by wafer level test and measurement of initial offset and sensitivity
- Zero-g level and sensitivity are essentially rati ometric to supply voltage at the calibration level
- Contribution to the measuring output of an inclination/acceleration along any perpendicular axis
- “Self test output voltage change” is defined as Vout
- Minimum resonance frequency Fres=4 .0kHz. Sensor bandwidth=1/(2*π*32kΩ*Cload)
2.2 Electrical characteristics
Table 4. Electrical characteristics (1)
- The product is factory calibrated at 3.0V
- Typical specificat ions are not guaranteed
2.3 Absolute maximum ratings
2.4 Terminology
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. tolerance describes the range of Zero-g levels of a population of sensors. Table 5. Absolute maximum ratings
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.
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.
4 Application hints
Figure 3. LIS244AL Electrical connection be placed as near as possible to the device (common design practice).
4.1 Soldering information
The LGA package is compliant with the ECOPACK, RoHs and “Green” standard. Figure 4. Output response vs. orientation Figure 4 refers to LIS244AL powered at 3.0V. Table 6. Filter Capacitor Selection, C load (x,y),
1 Hz 5 µF
20 Hz 250nF
50 Hz 100nF
100 Hz 50nF
200 Hz 25nF
500 Hz 10nF
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
6 Revision history
Table 7. Document revision history