Document Number: MMA7331LC
Rev 3, 08/2011
Freescale Semiconductor
Data Sheet: Technical Data
© Freescale Semiconductor, Inc., 2010, 2011 . All rights reserved.
±4g, ±9g Three Axis Low-g
Micromachined Accelerometer
The MMA7331LC 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 two sensitivities. Zero-g offset and sensitivity are factory
set and require no external devices. The MMA7331LC includes a Sleep Mode
which makes it ideal for handh eld battery powered electronics.
Features
• 3mm x 5mm x 1.0mm LGA-14 Package
• Low Current Consumption: 400 μA
• Sleep Mod e : 3 μA
• Low Voltage Operation: 2.2 V – 3.6 V
• Selectable Sensitivity (±4g, ±9g)
• 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
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, eCompass
• Pedometer: Motion Sensing
• PDA: Text Scroll
• Navigation and Dead Reckoning: eCompass Tilt Compensation
• Robotics: Motion Sensing
ORDERING INFORMATION
Part Number Temperature
Range Package
Drawing Package Shipping
MMA7331LCT -40 to +85°C 1977-01 LGA-14 Tray
MMA7331LCR1 -40 to +85°C 1977-01 LGA-14 7” Tape & Reel
MMA7331LCR2 -40 to +85°C 1977-01 LGA-14 13” Tape & Reel
MMA7331LC
MMA7331LC: XYZ AXIS
ACCELEROMETER
±4g, ±9g
14 LEAD
LGA
CASE 1977-01
Bottom View
Figure 1. Pin Connectio ns
Top View
123456
7
8 9 10 11 12 13
14
N/C
X
OUT
Z
OUT
Y
OUT
V
SS
V
DD
Sleep
N/C
N/C
g-Select
Self Test
N/C
N/C
N/C
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2Freescale Semiconductor
MMA7331LC
Figure 2. Simplified Accelerometer Functional Block Diagram
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.
Table 1. Maximum Ratings
(Maximum ratings are the limits to which the device can be exposed without causing pe rmanent damage.)
Rating Symbol Value Unit
Maximum Acceleration (all axis) gmax ±5000 g
Supply Voltage VDD –0.3 to +3.6 V
Drop Test(1)
1. Dropped onto concrete surf ace from any axis.
Ddrop 1.8 m
Storage Temperature Range Tstg –40 to +125 °C
Sleep
Self Test
C to V
CONVERTER
XOUT
YOUT
ZOUT
OSCILLATOR CLOCK
GEN
g-Select
X-TEMP
COMP
G-CELL
SENSOR GAIN
+
FILTER
CONTROL LOGIC
NVM TRIM
CIRCUITS
Y-TEMP
COMP
Z-TEMP
COMP
VDD
VSS
SELFTEST
Sleep
Self Test
C to V
CONVERTER
XOUT
YOUT
ZOUT
OSCILLATOR CLOCK
GEN
g-Select
X-TEMP
COMP
G-CELL
SENSOR GAIN
+
FILTER
CONTROL LOGIC
NVM TRIM
CIRCUITS
Y-TEMP
COMP
Z-TEMP
COMP
VDD
VSS
SELFTEST
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MMA7331LC
Table 2. Operating Characteristics
Unless otherwise noted: -40°C < TA < 85°C, 2.2 V < VDD < 3.6 V, Acceleration = 0g, Loaded output(1)
Characteristic Symbol Min Typ Max Unit
Operating Range(2)
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
VDD
IDD
IDD
TA
gFS
gFS
2.2
—
—
-40
—
—
2.8
400
3
—
±4
±9
3.6
600
10
+85
—
—
V
μA
μA
°C
g
g
Output Signal
Zero g (TA = 25°C, VDD = 2.8 V)(5), (6)
XY
Z (7)
Zero g Temperature Coefficient(8)
X
Y
Z
Sensitivity (TA = 25°C, VDD = 2.8 V)
4g
9g
Sensitivity(4)
Bandwidth Response
XY
Z
Output Impedance
VOFF
VOFF
TCO4g
TCO9g
TCO9g
TCO9g
S4g
S9g
S,TA
f-3dBXY
f-3dBZ
ZO
1.316
1.45
-2
-12
-7.9
-8.4
289.5
75.2
-0.0075
—
—
24
1.4
1.4
±0.5
-6.4
-0.9
0
308
83.6
±0.002
400
300
32
1.484
1.484
2
-0.6
5.2
8.5
326.5
91.9
+0.0075
—
—
40
V
V
mg/°C
mg/°C
mg/°C
mg/°C
mV/g
mV/g
%/°C
Hz
Hz
kΩ
Self Test
Output Response
XOUT, YOUT
ZOUT
Input Low
Input High
ΔgSTXY
ΔgSTZ
VIL
VIH
+0.05
+0.5
VSS
0.7 VDD
-0.1
+1.75
—
—
—
+3.0
0.3 VDD
VDD
g
g
V
V
Noise
Power Spectral Density RMS (0.1 Hz – 1 kHz)(4) nPSD — 350 — μg/
Control Timing
Power-Up Response Time(9)
Enable Response Time(10)
Self Test Response Time(11)
Sensing Element Resonant Frequency
XY
Z
Internal Sampling Frequency
tRESPONSE
tENABLE
tST
fGCELLXY
fGCELLZ
fCLK
—
—
—
—
—
—
1.0
0.5
2.0
6.0
3.4
11
2.0
2.0
5.0
—
—
—
ms
ms
ms
kHz
kHz
kHz
Output Stage Performance
Full-Scale Output Range (IOUT = 3 µA) VFSO VSS+0.1 — VDD–0.1 V
Nonlinearity, XOUT, YOUT, ZOUT NLOUT -1.0 — +1.0 %FSO
Cross-Axis Sensitivity(12) VXY, XZ, YZ -5.0 — +5.0 %
1. For a loaded output, the measurements are observed after an RC filter consisting of an internal 32 kΩ resistor and an exte rnal 3 .3 n F cap acito r
(recommended as a minimum to filt er clock noise) on the analog output for each axis and a 0.1 μF capa citor on VDD - GND. The output senso r
bandwidth is determined by the Capacitor added on the output. f = 1/2π * (32 x 10 3) * C. C = 3.3 nF corresponds to BW = 1507 Hz, which is the minimum
to filter out intern al clock nois e.
2. These limits defin e th e ran g e of op er at ion for whic h the pa rt 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 4g 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 ab ove VDD/2. For negative ac ce le ration, the output will dec re as e be lo w VDD/2.
6. For optimal 0g offset perf ormance, adhe re to AN3484 and AN3447.
7. Product per formance will not exceed this minimu m level, however, measure ment over time will not be equa l to time zero measurements for this specific
parameter.
8. X, Y, Z = 0g
9. The response time between 1 0% of full scale V DD input voltage and 90% of the final operating output voltage.
10. The response time between 10% of full scale Sleep Mode input voltage and 90% of the final operating output voltage.
11. The response time between 10% of the full scale self test input voltage and 90% of the self test output voltage.
12. A measure of the device’s ability to reject an accelera tion applied 90° from the true a xis of sensitivity.
Hz
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4Freescale Semiconductor
MMA7331LC
PRINCIPLE OF OPERAT ION
The Freescal e accelerometer is a s urface-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 semiconducto r
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 = Aε/D). Where A is the area of the
beam, ε 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.
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 initia ted, 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 procedu re assures that both the
mechanical (g-cell) and electronic sections of the
accelerometer are functioning.
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 4g or 9g 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 4g
sensitivity as the device has an internal pull-down to keep it
at that sensitivity (308 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 μA typ. For lower power consumption, it is
recommended to set g-Select to 4g 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 volt age 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.
Acceleration
Table 3. g-Select Pin Description
g-Select g-Range Sensitivity
04g 308 mV/g
19g 83.6 mV/g
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MMA7331LC
BASIC CONNECTIONS
Pin Descriptions
Figure 4. Pinout Description
Figure 5. Acce lerometer with Recommended
Connection Diagram
PCB Layout
Figure 6. Recommende d PCB La y out for Interfacing
Accelerometer to Microcontroller
NOTES:
1. Use 0.1 µF 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 3.3 nF 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 inte rfere with the internal accelerometer
sampling frequency (11 kHz for the sampling
frequency). This will prevent aliasing errors.
8. 10 MΩ or higher is recommended on XOUT, YOUT and
ZOUT to prevent loss due to the voltage divider
relationship between the internal 32 kΩ resistor and
the measurement input impedance.
Table 4. Pin Descriptions
Pin No.
Pin Name Description
1N/C
No internal connection
Leave unconnected
2X
OUT X direction output voltage
3Y
OUT Y direction output voltage
4Z
OUT Z direction output voltage
5 VSS Power Supply Ground
6V
DD Power Supply Input
7Sleep
Logic input pin to enable product or Sleep Mode
8N/C
No internal connection
Leave unconnected
9N/C
No internal connection
Leave unconnected
10 g-Select Logic input pin to select g level
11 N/C Unused for factory trim
Leave unconnected
12 N/C Unused for factory trim
Leave unconnected
13 Self Test Input pin to initiate Self Test
14 N/C Unused for factory trim
Leave unconnected
123456
7
8 9 10 11 12 13
14
N/C
XOUT
ZOUT
YOUT
VSS
VDD
Sleep
N/C
N/C
g-Select
Self Test
N/C
N/C
N/C
Top View
2
3
4
3.3 nF
3.3 nF
3.3 nF
13
10
6
5
7
Logic
Input
Logic
Input
Logic
Input
0.1 μF
VDD
VDD
VSS
g-Select
Self Test
Sleep
XOUT
YOUT
ZOUT
MMA7331L
MMA7331LC
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6Freescale Semiconductor
MMA7331LC
Side View
XOUT @0g=1.4V
YOUT @ +1g = 1.708 V
ZOUT @0g=1.4V
XOUT @ +1g = 1.708 V
YOUT @0g=1.4V
ZOUT @0g=1.4V
XOUT @ -1g = 1.092 V
YOUT @0g=1.4V
ZOUT @0g=1.4V
XOUT @0g=1.4V
YOUT @ -1g = 1.092 V
ZOUT @0g=1.4V
Direction of Earth's gravity field.*
Top View
XOUT @0g=1.4V
YOUT @0g=1.4V
ZOUT @ -1g = 1.708 V
XOUT @0g=1.4V
YOUT @0g=1.4V
ZOUT @ +1g = 1.708 V
Top
Top
Bottom
Bottom
123456
7
8 9 10 11 12 13
14
123456
7
8 9 10 11 12 13
14
13 12 11 10 9 8
12 34 56
14 7
123456
7
8 9 10 11 12 13
14
Top View
Side View
+Y
-Y
+X +Z-X -Z
Top
Bottom
: Arrow indicates direction of package movement.
14-Pin LGA Package
123456
7
8 9 10 11 12 13
14
DYNAMIC ACCELERATION
STATIC ACCELERATION
* When positioned as shown, the Earth’s gravity will result in a positive 1g output.
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MMA7331LC
Figure 7. MMA7331LC (4g only) Temperature Coefficient of Offset (TCO) and
Temperature Coefficient of Sensitivity (TC S) Distributio n Charts
LSL USLTarget
-2 -1 0 1 2
X-TCO mg/degC
LSL USLTarget
-2 -1 0 1 2
Y-TCO mg/degC
LSL USLTarget
-2 -1 0 1 2
Z- TCO mg/ degC
LSL USLTarget
-0.01 -0.005 0.005 .01
X-TCS %/degC
LSL USLTarget
-0.01 -0.005 0.005 .01
Y-TCS %/degC
LSL USLTarget
-0.01 -0.005 0.005 .01
Z-TC S %/ degC
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MMA7331LC
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 shorti ng between solder pads.
Figure 8. LGA 14-Lead, 5 x 3 mm Die Sensor
6x2
12x1
14x0.9
14x0.6
10x0.8
113
68
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Freescale Semiconductor 9
MMA7331LC
PACKAGE DIMENSIONS
CASE 1977-01
ISSUE A
14-LEAD LGA
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10 Freescale Semiconductor
MMA7331LC
PACKAGE DIMENSIONS
CASE 1977-01
ISSUE A
14-LEAD LGA
MMA7331LC
Rev. 3
08/2011
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