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Freescale Semiconductor Technical Data
Document Number: MMA7340L Rev 2, 8/2007
3g, 11g Three Axis Low-g Micromachined Accelerometer
The MMA7340L is a low power, low profile capacitive micromachined accelerometer featuring signal conditioning, a 1-pole low pass filter, temperature compensation, self test, and g-Select which allows for the selection between 2 sensitivities. Zero-g offset and sensitivity are factory set and require no external devices. The MMA7340L includes a Sleep Mode that makes it ideal for handheld battery powered electronics. Features * * * * * * * * * * * * 3mm x 5mm x 1.0mm LGA-14 Package Low Current Consumption: 400 A Sleep Mode: 3 A Low Voltage Operation: 2.2 V - 3.6 V Selectable Sensitivity (3g, 11g) Fast Turn On Time (0.5 ms Enable Response Time) Self Test for Freefall Detect Diagnosis Signal Conditioning with Low Pass Filter Robust Design, High Shocks Survivability RoHS Compliant Environmentally Preferred Product Low Cost
MMA7340L
MMA7340L: XYZ AXIS ACCELEROMETER 3g, 11g
Bottom View
Typical Applications * * * * * * * * 3D Gaming: Tilt and Motion Sensing, Event Recorder HDD MP3 Player: Freefall Detection Laptop PC: Freefall Detection, Anti-Theft Cell Phone: Image Stability, Text Scroll, Motion Dialing, E-Compass Pedometer: Motion Sensing PDA: Text Scroll Navigation and Dead Reckoning: E-Compass Tilt Compensation Robotics: Motion Sensing
14 LEAD LGA CASE 1935-01
Top View
N/C N/C XOUT YOUT 1 2 3 4 5 6 7 Sleep
Figure 1. Pin Connections
14
13 Self Test 12 N/C 11 N/C 10 g-Select 9 N/C 8 N/C
ORDERING INFORMATION
Part Number MMA7340LT MMA7340LR2 Temperature Range -40 to +85C -40 to +85C Package Drawing 1935-01 1935-01 Package LGA-14 LGA-14 Shipping Tray Tape & Reel
ZOUT VSS VDD
(c) Freescale Semiconductor, Inc., 2007. All rights reserved.
VDD
g-Select CLOCK GEN X-TEMP COMP
OSCILLATOR
XOUT
Sleep
G-CELL SENSOR
C to V CONVERTER
GAIN + FILTER
Y-TEMP COMP
YOUT
SELFTEST Self Test
CONTROL LOGIC NVM TRIM CIRCUITS
Z-TEMP COMP
ZOUT
VSS
Figure 2. Simplified Accelerometer Functional Block Diagram
Table 1. Maximum Ratings (Maximum ratings are the limits to which the device can be exposed without causing permanent damage.)
Rating Maximum Acceleration (all axis) Supply Voltage Drop Test(1) Symbol gmax VDD Ddrop Tstg Value 5000 -0.3 to +3.6 1.8 -40 to +125 Unit g V m C
Storage Temperature Range 1. Dropped onto concrete surface from any axis.
ELECTRO STATIC DISCHARGE (ESD)
WARNING: This device is sensitive to electrostatic discharge. Although the Freescale accelerometer contains internal 2000 V ESD protection circuitry, extra precaution must be taken by the user to protect the chip from ESD. A charge of over 2000 volts can accumulate on the human body or associated test equipment. A charge of this magnitude can alter the performance or cause failure of the chip. When handling the accelerometer, proper ESD precautions should be followed to avoid exposing the device to discharges which may be detrimental to its performance.
MMA7340L 2 Sensors Freescale Semiconductor
Table 2. Operating Characteristics Unless otherwise noted: -20C < TA < 85C, 2.2 V < VDD < 3.6 V, Acceleration = 0g, Loaded output(1)
Characteristic Operating Range Supply Voltage(3) Supply Current(4) Supply Current at Sleep Mode(4) Operating Temperature Range Acceleration Range, X-Axis, Y-Axis, Z-Axis g-Select: 0 g-Select: 1 Output Signal Zero g (TA = 25C, VDD = 3.3 V)(5), (6) Zero g(4) Sensitivity (TA = 25C, VDD = 3.3 V) 3g 11g Sensitivity(4) Bandwidth Response XY Z Output Impedance Self Test Output Response XOUT, YOUT ZOUT Input Low Input High Noise Power Spectral Density RMS (0.1 Hz - 1 kHz)(4) Control Timing Power-Up Response Time(7) Enable Response Time(8) Self Test Response Time(9) Sensing Element Resonant Frequency XY Z Internal Sampling Frequency Output Stage Performance Full-Scale Output Range (IOUT = 30 A) Nonlinearity, XOUT, YOUT, ZOUT Cross-Axis Sensitivity(10)
(2)
Symbol VDD IDD IDD TA gFS gFS VOFF VOFF, TA S3g S11g S,TA f-3dBXY f-3dBZ ZO
Min 2.2 -- -- -40 -- -- 1.551 -- 413.6 106 -- -- -- --
Typ 3.3 400 3 -- 3 11 1.65 2.0 440 117.8 0.03 400 300 32
Max 3.6 600 10 +85 -- -- 1.749 -- 466.4 129.6 -- -- -- --
Unit V A A C g g V mg/C mV/g mV/g %/C Hz Hz k
gSTXY gSTZ VIL VIH nPSD tRESPONSE tENABLE tST fGCELLXY fGCELLZ fCLK VFSO NLOUT VXY, XZ, YZ
+0.05 +0.8 VSS 0.7 VDD -- -- -- -- -- -- -- VSS+0.1 -1.0 -5.0
-0.1 +1.0 -- -- 350 1.0 0.5 2.0 6.0 3.4 11 -- -- --
-- +1.2 0.3 VDD VDD -- 2.0 2.0 5.0 -- -- -- VDD-0.1 +1.0 +5.0
g g V V g/ Hz ms ms ms kHz kHz kHz V %FSO %
1. For a loaded output, the measurements are observed after an RC filter consisting of an internal 32k resistor and an external 3.3nF capacitor (recommended as a minimum to filter clock noise) on the analog output for each axis and a 0.1F capacitor on VDD - GND. The output sensor bandwidth is determined by the Capacitor added on the output. f = 1/2 * (32 x 103) * C. C = 3.3 nF corresponds to BW = 1507HZ, which is the minimum to filter out internal clock noise. 2. These limits define the range of operation for which the part will meet specification. 3. Within the supply range of 2.2 and 3.6 V, the device operates as a fully calibrated linear accelerometer. Beyond these supply limits the device may operate as a linear device but is not guaranteed to be in calibration. 4. This value is measured with g-Select in 3g mode. 5. The device can measure both + and - acceleration. With no input acceleration the output is at midsupply. For positive acceleration the output will increase above VDD/2. For negative acceleration, the output will decrease below VDD/2. 6. For optimal 0g offset performance, adhere to AN3484 and AN3447 7. The response time between 10% of full scale Vdd input voltage and 90% of the final operating output voltage. 8. The response time between 10% of full scale Sleep Mode input voltage and 90% of the final operating output voltage. 9. The response time between 10% of the full scale self test input voltage and 90% of the self test output voltage. 10. A measure of the device's ability to reject an acceleration applied 90 from the true axis of sensitivity.
MMA7340L Sensors Freescale Semiconductor 3
PRINCIPLE OF OPERATION
The Freescale accelerometer is a surface-micromachined integrated-circuit accelerometer. The device consists of a surface micromachined capacitive sensing cell (g-cell) and a signal conditioning ASIC contained in a single package. The sensing element is sealed hermetically at the wafer level using a bulk micromachined cap wafer. The g-cell is a mechanical structure formed from semiconductor materials (polysilicon) using semiconductor processes (masking and etching). It can be modeled as a set of beams attached to a movable central mass that move between fixed beams. The movable beams can be deflected from their rest position by subjecting the system to an acceleration (Figure 3). As the beams attached to the central mass move, the distance from them to the fixed beams on one side will increase by the same amount that the distance to the fixed beams on the other side decreases. The change in distance is a measure of acceleration. The g-cell beams form two back-to-back capacitors (Figure 3). As the center beam moves with acceleration, the distance between the beams changes and each capacitor's value will change, (C = A/D). Where A is the area of the beam, is the dielectric constant, and D is the distance between the beams. The ASIC uses switched capacitor techniques to measure the g-cell capacitors and extract the acceleration data from the difference between the two capacitors. The ASIC also signal conditions and filters (switched capacitor) the signal, providing a high level output voltage that is ratiometric and proportional to acceleration. Acceleration g-Select The g-Select feature allows for the selection between two sensitivities. Depending on the logic input placed on pin 10, the device internal gain will be changed allowing it to function with a 3g or 11g sensitivity (Table 3). This feature is ideal when a product has applications requiring two different sensitivities for optimum performance. The sensitivity can be changed at anytime during the operation of the product. The g-Select pin can be left unconnected for applications requiring only a 3g sensitivity as the device has an internal pull-down to keep it at that sensitivity (440mV/g)). Table 3. g-Select Pin Description
g-Select 0 1 g-Range 3g 11g Sensitivity 440 mV/g 117.5 mV/g
Sleep Mode The 3 axis accelerometer provides a Sleep Mode that is ideal for battery operated products. When Sleep Mode is active, the device outputs are turned off, providing significant reduction of operating current. A low input signal on pin 7 (Sleep Mode) will place the device in this mode and reduce the current to 3 A typ. For lower power consumption, it is recommended to set g-Select to 3g mode. By placing a high input signal on pin 7, the device will resume to normal mode of operation. Filtering The 3 axis accelerometer contains an onboard single-pole switched capacitor filter. Because the filter is realized using switched capacitor techniques, there is no requirement for external passive components (resistors and capacitors) to set the cut-off frequency. Ratiometricity Ratiometricity simply means the output offset voltage and sensitivity will scale linearly with applied supply voltage. That is, as supply voltage is increased, the sensitivity and offset increase linearly; as supply voltage decreases, offset and sensitivity decrease linearly. This is a key feature when interfacing to a microcontroller or an A/D converter because it provides system level cancellation of supply induced errors in the analog to digital conversion process.
Figure 3. Simplified Transducer Physical Model SPECIAL FEATURES Self Test The sensor provides a self test feature that allows the verification of the mechanical and electrical integrity of the accelerometer at any time before or after installation. This feature is critical in applications such as hard disk drive protection where system integrity must be ensured over the life of the product. Customers can use self test to verify the solderability to confirm that the part was mounted to the PCB correctly. When the self test function is initiated, an electrostatic force is applied to each axis to cause it to deflect. The x- and y-axis are deflected slightly while the z-axis is trimmed to deflect 1g. This procedure assures that both the mechanical (g-cell) and electronic sections of the accelerometer are functioning. MMA7340L 4
Sensors Freescale Semiconductor
BASIC CONNECTIONS
Pin Descriptions Top View PCB Layout
N/C N/C XOUT YOUT ZOUT VSS VDD 1 2 3 4 5 6 7 Sleep 14 13 Self Test 12 N/C 11 N/C 10 g-Select
Connection Diagram
POWER SUPPLY
VDD VSS Sleep Accelerometer g-Select Self Test XOUT YOUT C C C C C
VRH P0 P1 P2 A/DIN A/DIN A/DIN Microcontroller
VDD VSS
C
9 N/C 8 N/C
Figure 4. Pinout Description Table 4. Pin Descriptions
Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Pin Name N/C XOUT YOUT ZOUT VSS VDD Sleep N/C N/C g-Select N/C N/C Self Test N/C Description No internal connection Leave unconnected X direction output voltage Y direction output voltage Z direction output voltage Power Supply Ground Power Supply Input Logic input pin to enable product or Sleep Mode No internal connection Leave unconnected No internal connection Leave unconnected Logic input pin to select g level Unused for factory trim Leave unconnected Unused for factory trim Leave unconnected Input pin to initiate Self Test Unused for factory trim Leave unconnected
ZOUT
Figure 6. Recommended PCB Layout for Interfacing Accelerometer to Microcontroller NOTES: 1. Use 0.1 F capacitor on VDD to decouple the power source. 2. Physical coupling distance of the accelerometer to the microcontroller should be minimal. 3. Place a ground plane beneath the accelerometer to reduce noise, the ground plane should be attached to all of the open ended terminals shown in Figure 6. 4. Use a 3.3nF capacitor on the outputs of the accelerometer to minimize clock noise (from the switched capacitor filter circuit). 5. PCB layout of power and ground should not couple power supply noise. 6. Accelerometer and microcontroller should not be a high current path. 7. A/D sampling rate and any external power supply switching frequency should be selected such that they do not interfere with the internal accelerometer sampling frequency (11 kHz for the sampling frequency). This will prevent aliasing errors. 8. 10M or higher is recommended on XOUT, YOUT and ZOUT to prevent loss due to the voltage divider relationship between the internal 32 k resistor and the measurement input impedance.
Logic Input
10
g-Select XOUT 2
VDD
Logic Input
13
Self Test
3.3 nF
MMA7340L
6 0.1 F 5 VSS VDD YOUT
3
3.3 nF
ZOUT
4 3.3 nF
Logic Input
7
Sleep
Figure 5. Accelerometer with Recommended MMA7340L Sensors Freescale Semiconductor 5
DYNAMIC ACCELERATION
STATIC ACCELERATION
Top View
6 7 8 14 10 11 12 13
X Z
Direction of Earth's gravity field.*
2 1 14
5
4
3
9
OUT OUT
10 11 12 13 7
@ 0g = 1.65 V @ +1g = 2.09 V @ 0g = 1.65 V
Side View Top
8 6
1
2
Y
Bottom
X
OUT OUT
9
5
3
OUT
@ 0g = 1.65 V @ 0g = 1.65 V @ +1g = 2.09 V
10 11 12 13
4
Y Z
4
3
OUT
5
9
2
6
8
Bottom Top
X Z
OUT OUT
1
7
14
X Y Z
OUT OUT
@ +1g = 2.09 V @ 0g = 1.65 V @ 0g = 1.65 V
13 12 11 10 14 1
X Z
9
8 7
X Y Z
OUT OUT
@ -1g = 1.21 V @ 0g = 1.65 V @ 0g = 1.65 V
@ 0g = 1.65 V @ 0g = 1.65 V @ -1g = 1.21 V
Y
OUT
OUT
OUT
2
OUT OUT
3
4
5
6
@ 0g = 1.65 V @ -1g = 1.21 V @ 0g = 1.65 V
Y
OUT
* When positioned as shown, the Earth's gravity will result in a positive 1g output.
MMA7340L 6 Sensors Freescale Semiconductor
MINIMUM RECOMMENDED FOOTPRINT FOR SURFACE MOUNTED APPLICATIONS
PCB Mounting Recommendations MEMS based sensors are sensitive to Printed Circuit Board (PCB) reflow processes. For optimal zero-g offset after PCB mounting, care must be taken to PCB layout and reflow conditions. Reference application note AN3484 for best practices to minimize the zero-g offset shift after PCB mounting. Surface mount board layout is a critical portion of the total design. The footprint for the surface mount packages must be the correct size to ensure proper solder connection interface between the board and the package. With the correct footprint, the packages will self-align when subjected to a solder reflow process. It is always recommended to design boards with a solder mask layer to avoid bridging and shorting between solder pads.
1
13
10x0.8
6x2
6 8 14x0.6 14x0.9 12x1
Figure 7. LGA 14-Lead, 5 x 3 mm Die Sensor
MMA7340L Sensors Freescale Semiconductor 7
PACKAGE DIMENSIONS
CASE 1935-01 ISSUE 0 14-LEAD LGA
MMA7340L 8 Sensors Freescale Semiconductor
PACKAGE DIMENSIONS
CASE 1935-01 ISSUE 0 14-LEAD LGA
MMA7340L Sensors Freescale Semiconductor 9
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RoHS-compliant and/or Pb-free versions of Freescale products have the functionality and electrical characteristics of their non-RoHS-compliant and/or non-Pb-free counterparts. For further information, see http:/www.freescale.com or contact your Freescale sales representative. For information on Freescale's Environmental Products program, go to http://www.freescale.com/epp. MMA7340L Rev. 2 8/2007

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