Freescale Semiconductor
Data Sheet: Technical Data
MMA3221KEG
Rev 1, 11/2012
Surface Mount
Micromachined Accelerometer
The MMA3221 series of dual axis (X and Y) silicon capacitive,
micromachined accelerometers features signal conditioning, a 4-pole low
pass filter and temperature compensation and separate outputs for the two
axes. Zero-g offset full scale span and filter cut-off are factory set and require
no external devices. A full system self-test capability verifies system
functionality.
Features
• Sensitivity in two separate axes: 50g X-axis and 20g Y-axis
• Integral Signal Conditioning
• Linear Output
• Ratiometric Performance
• 4th Order Bessel Filter Preserves Pulse Shape Integrity
• Calibrated Self-test
• Low Voltage Detect, Clock Monitor, and EPROM Parity Check Status
• Transducer Hermetically Sealed at Wafer Level for Superior Reliability
• Robust Design, High Shocks Survivability
• Qualified AEC-Q100, Rev. F Grade 2 (-40C/ +105C)
Typical Applications
• Vibration Monitoring and Recording
• Impact Monitoring
• Appliance Control
• Mechanical Bearing Monitoring
• Computer Hard Drive Protection
• Computer Mouse and Joysticks
• Virtual Reality Input Devices
• Sports Diagnostic Devices and Systems
ORDERING INFORMATION
Device
MMA3221EG
MMA3221EGR2
MMA3221KEG*
MMA3221KEGR2*
Temperature Range
–40 to +125°C
–40 to +125°C
–40 to +125°C
–40 to +125°C
Case No.
475A-02
475A-02
475A-02
475A-02
Package
SOIC-20
SOIC-20, Tape & Reel
SOIC-20
SOIC-20, Tape & Reel
MMA3221KEG
MMA3221KEG: XY-AXIS SENSITIVITY
MICROMACHINED
ACCELEROMETER
±50/20g
KEG SUFFIX (Pb-FREE)
20-LEAD SOIC
CASE 475A-02
*Part number sourced from a different facility.
AV
DD
V
DD
N/C
N/C
N/C
N/C
ST
X
OUT
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
GND
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
Y
OUT
G-Cell
Sensor
Integrator
Gain
Filter
Temp
X
OUT
Y
OUT
ST
Self-Test
Control Logic &
EPROM
Trim Circuits
Oscillator
Clock
Gen.
V
SS
STATUS
V
SS
V
DD
AV
DD
Status
Figure 1. Simplified Accelerometer Functional Block Diagram
Figure 2. Pin Connections
© 2011, 2012 Freescale Semiconductor, Inc. All rights reserved.
Table 1. Maximum Ratings
(Maximum ratings are the limits to which the device can be exposed without causing permanent damage.)
Rating
Powered Acceleration (all axes)
Unpowered Acceleration (all axes)
Supply Voltage
Drop Test
(1)
Storage Temperature Range
NOTES:
1. Dropped onto concrete surface from any axis.
Symbol
G
pd
G
upd
V
DD
D
drop
T
stg
Value
1500
2000
–0.3 to +7.0
1.2
–40 to +125
Unit
g
g
V
m
°C
ELECTRO STATIC DISCHARGE (ESD)
WARNING: This device is sensitive to electrostatic
discharge.
Although the Freescale accelerometers contain internal
2kV 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.
MMA3221KEG
2
Sensors
Freescale Semiconductor, Inc.
Table 2. Operating Characteristics
(Unless otherwise noted: –40°C
T
A
+105°C,
4.75
V
DD
5.25,
Acceleration = 0g, Loaded output.
(1)
)
Characteristic
Operating Range
(2)
Supply Voltage
(3)
Supply Current
Operating Temperature Range
Acceleration Range X-axis
Acceleration Range Y-axis
Output Signal
Zero g X-axis (T
A
= 25°C, V
DD
= 5.0 V)
(4)
Zero g Y-axis (T
A
= 25°C, V
DD
= 5.0 V)
(4)
Zero g X-axis
Zero g Y-axis
Sensitivity X-axis (T
A
= 25°C, V
DD
= 5.0 V)
(5)
Sensitivity Y-axis (T
A
= 25°C, V
DD
= 5.0 V)
(5)
Sensitivity X-axis
Sensitivity Y-axis
Bandwidth Response
Nonlinearity
Noise
RMS (.01 Hz – 1 kHz)
Power Spectral Density
Clock Noise (without RC load on output)
(6)
Self-Test
Output Response
(7)
Input Low
Input High
Input Loading
(8)
Response Time
(9)
Status
(13)(14)
Output Low (I
load
= 100
A)
Output High (I
load
= 100
A)
Minimum Supply Voltage (LVD Trip)
Clock Monitor Fail Detection Frequency
Output Stage Performance
Electrical Saturation Recovery Time
(10)
Full Scale Output Range (I
OUT
= 200
A)
Capacitive Load Drive
(11)
Output Impedance
Mechanical Characteristics
Transverse Sensitivity
(12)
Package Resonance
NOTES:
1. For a loaded output the measurements are observed after an RC filter consisting of a 1 k resistor and a 0.01
F
capacitor to ground.
Symbol
V
DD
I
DD
T
A
g
FS
g
FS
V
OFF
V
OFF
V
OFF,V
V
OFF,V
S
S
S
V
S
V
f
–3dB
NL
OUT
n
RMS
n
PSD
n
CLK
g
ST
V
IL
V
IH
I
IN
t
ST
V
OL
V
OH
V
LVD
f
min
t
DELAY
V
FSO
C
L
Z
O
V
XZ,YZ
f
PKG
Min
4.75
6
–40
—
—
2.30
2.30
0.41 V
DD
0.44 V
DD
38
95
7.44
18.6
360
–1.0
—
—
—
9.6
V
SS
0.7
V
DD
–30
—
—
V
DD
–0.8
2.7
50
—
0.25
—
—
—
—
Typ
5.00
8
—
112.5
33.75
2.5
2.5
0.50 V
DD
0.50 V
DD
40
100
8
20
400
—
—
110
2.0
12
—
—
–100
2.0
—
—
3.25
—
0.2
—
—
300
—
10
Max
5.25
10
+125
—
—
2.70
2.70
0.56 V
DD
0.56 V
DD
42
105
8.56
21.4
440
+1.0
2.8
—
—
14.4
0.3
V
DD
V
DD
–300
–
0.4
—
4.0
260
—
V
DD
– 0.25
100
—
5.0
—
Unit
V
mA
°C
g
g
V
V
V
V
mV/g
mV/g
mV/g/V
mV/g/V
Hz
% FSO
mVrms
V/(Hz
1/2
)
mVpk
g
V
V
A
ms
V
V
V
kHz
ms
V
pF
% FSO
kHz
2. These limits define the range of operation for which the part will meet specification.
3. Within the supply range of 4.75 and 5.25 volts, 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. The device can measure both + and – acceleration. With no input acceleration the output is at mid-supply. For positive acceleration the
output will increase above V
DD
/2 and for negative acceleration the output will decrease below V
DD
/2.
5. The device is calibrated at 20g.
6. At clock frequency
70
kHz.
7.
V
OFF
calculated with typical sensitivity.
8. The digital input pin has an internal pull-down current source to prevent inadvertent self test initiation due to external board level leakages.
9. Time for the output to reach 90% of its final value after a self-test is initiated.
10. Time for amplifiers to recover after an acceleration signal causing them to saturate.
11. Preserves phase margin (60°) to guarantee output amplifier stability.
12. A measure of the device's ability to reject an acceleration applied 90° from the true axis of sensitivity.
13. The Status pin output is not valid following power-up until at least one rising edge has been applied to the self-test pin. The Status pin is
high whenever the self-test input is high, as a means to check the connectivity of the self-test and Status pins in the application.
14. The Status pin output latches high if a Low Voltage Detection or Clock Frequency failure occurs, or the EPROM parity changes to odd. The
Status pin can be reset low if the self-test pin is pulsed with a high input for at least 100
s,
unless a fault condition continues to exist.
MMA3221KEG
Sensors
Freescale Semiconductor, Inc.
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 CMOS signal
conditioning ASIC contained in a single integrated circuit
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 two
stationary plates with a moveable plate in-between. The
center plate can be deflected from its rest position by
subjecting the system to an acceleration (Figure
3).
When the center plate deflects, the distance from it to one
fixed plate will increase by the same amount that the distance
to the other plate decreases. The change in distance is a
measure of acceleration.
The g-cell plates form two back-to-back capacitors
(Figure
4).
As the center plate moves with acceleration, the
distance between the plates changes and each capacitor's
value will change, (C = A/D). Where A is the area of the
plate,
is the dielectric constant, and D is the distance
between the plates.
The CMOS 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
Figure 3. Transducer
Physical Model
Figure 4. Equivalent
Circuit Model
SPECIAL FEATURES
Filtering
The Freescale accelerometers contain an onboard 2-pole
switched capacitor filter. A Bessel implementation is used
because it provides a maximally flat delay response (linear
phase) thus preserving pulse shape integrity. 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.
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 automotive airbag
systems where system integrity must be ensured over the life
of the vehicle. A fourth “plate'' is used in the g-cell as a self-
test plate. When the user applies a logic high input to the self-
test pin, a calibrated potential is applied across the self-test
plate and the moveable plate. The resulting electrostatic
2
1
V
force
Fe
=
--
A
------
causes the center plate to deflect.
-
2
d
2
The resultant deflection is measured by the accelerometer's
control ASIC and a proportional output voltage results. This
procedure assures that both the mechanical (g-cell) and
electronic sections of the accelerometer are functioning.
Status
Freescale accelerometers include fault detection circuitry
and a fault latch. The Status pin is an output from the fault
latch, OR'd with self-test, and is set high whenever the
following event occurs:
• Parity of the EPROM bits becomes odd in number.
The fault latch can be reset by a rising edge on the self-test
input pin, unless one (or more) of the fault conditions
continues to exist.
MMA3221KEG
4
Sensors
Freescale Semiconductor, Inc.
BASIC CONNECTIONS
Pinout Description
PCB Layout
P1
P0
R
A/D In
Microcontroller
N/C
N/C
N/C
N/C
ST
X
OUT
STATUS
V
SS
V
DD
AV
DD
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
GND
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
Y
OUT
STATUS
Accelerometer
ST
X
OUT
1 k C
0.01
F
Y
OUT
V
SS
V
DD
V
SS
R
1 k
C
0.1
F
A/D In
C
0.01
F
C
V
DD
0.1
F
V
RH
C
0.1
F
Power Supply
Pin No.
1 thru 3
4
5
6
7
8
9
10
11
12 thru 16
17 thru 19
20
Pin Name
—
—
ST
X
OUT
STATUS
V
SS
V
DD
AV
DD
Y
OUT
—
—
GND
Description
Leave unconnected.
No internal connection. Leave
unconnected.
Logic input pin used to initiate
self-test.
Output voltage of the
accelerometer. X Direction.
Logic output pin to indicate
fault.
The power supply ground.
The power supply input.
Power supply input (Analog).
Output voltage of the
accelerometer. Y Direction.
Used for factory trim. Leave
unconnected.
No internal connection. Leave
unconnected.
Ground.
Figure 4. Recommended PCB Layout for Interfacing
Accelerometer to Microcontroller
NOTES:
• Use a 0.1
F
capacitor on V
DD
to decouple the power
source.
• Physical coupling distance of the accelerometer to the
microcontroller should be minimal.
• 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 4.
• Use an RC filter of 1 k and 0.01
F
on the output of the
accelerometer to minimize clock noise (from the switched
capacitor filter circuit).
• PCB layout of power and ground should not couple power
supply noise.
• Accelerometer and microcontroller should not be a high
current path.
• 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. This will prevent aliasing errors.
V
DD
Logic
Input
C1
0.1
F
5
9
10
8
MMA3221KEG
ST
V
DD
AV
DD
V
SS
Y
OUT
X
OUT
7
R1
1 k
Status
6
X Output
Signal
C2
0.01
F
R2
1 k
Y Output
Signal
11
C3
0.01
F
Figure 3. SOIC Accelerometer with Recommended
Connection Diagram
MMA3221KEG
Sensors
Freescale Semiconductor, Inc.
5
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