Document Number: MMA2241KEG
Rev 3, 11/2012
Freescale Semiconductor
Data Sheet: Technical Data
© 2011, 2012 Freescale Semiconductor, Inc. All rights reserved.
Surface Mount
Micromachined Accelerometer
The MMA2241KEG is a silicon capacitive, micromachined accelerometer
featuring signal conditioning, a 2-pole low pass filter and temperature
compensation. 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
• Integral Signal Conditioning
• Linear Output
• Ratiometric Performance
• 2nd Order Bessel Filter Preserves Pulse Shape Integrity
• Calibrated Self-test
• Low Voltage Detect, Clock Monitor, and EPROM Parity Check S tatus
• Transducer Hermetically Sealed at Wafer Level for Superior Reliability
• Robust Design, High Shocks Survivability
• Pb-Free Termination
• Environmentally Preferred Package
• Qualified AEC-Q100, Rev. F Grade 2 (-40C/ +105C)
Typical Applications
• Vibration Monitoring and Recording
• Dynamic Suspension Control
ORDERING INFORMATION
Device Name Temperature Range Case No. Package
MMA2241EG –40to 125C475-01 SOIC-16
MMA2241EGR2 –40to 125C475-01 SOIC-16, Tape & Reel
MMA2241KEG* –40to 125C475-01 SOIC-16
MMA2241KEGR2* –40to 125C475-01 SOIC-16, Tape & Reel
*Part number sourced from a different facility.
MMA2241KEG
X-AXIS SENSITIVITY
MICROMACHINED
ACCELEROMETER
±10g
KEG SUFFIX (Pb-FREE)
16-LEAD SOIC
CASE 475-01
G-Cell
Sensor Integrator Gain Filter Temp
Comp
Self-test Control Logic &
EPROM Trim Circuits Clock
Generator
Oscillator
VDD
VOUT
VSS
ST
STATUS
Figure 1. Simplified Accelerometer Functional Block Diagram
N/C
N/C
N/C
ST
VOUT
STATUS
VSS
VDD
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
Figure 2. Pin Connections
Document Number: MMA2241KEG
Sensors
2Freescale Semiconductor, Inc.
The block diagram of the MMA2241EG is shown in
Figure 1. The X-axis g-cell is constructed using surface
micromachining; and the interface IC is fabricated in a
1.2 micron (60%) silicon gate CMOS process.
The signal conditioning of the accele rometer channel
begins with a capacitance to voltage conversion (C to V)
followed by a 2-stage switched capacitor amplifier. This
2-stage amplifier has adjustable offset and gain trimming.
The offset and gain of the interface IC can be controlled by
the serially accessed EPROM trimming register.
Following the 2-stage amplifier the signal passes through
a 2-pole, switched capacitor filter with a Bessel characteristic.
The rolloff frequency of the filte r is trimmed by adjustin g the
frequency of the single on-chip oscillator. The frequency is
adjusted by trimming the bias current to the oscillator using
the EPROM trim register.
The output of the filter is then amplified by the output stage
which also has a temperature compensation circuit for
sensitivity which can be adjusted using the EPROM trim
register.
An adjustable self-test voltage to be applied to the
electrostatic deflection plate in the sensing element. Other
support circuits include a bandgap voltage reference for the
bias sources and the self-test voltage. The interface IC also
has its own power supply filter which feeds all the analog
functions in order to increase the power supply rejection ratio
(PSRR).
Included are several fault checks for low voltage detect
(L VD), clock and/or bias monitoring, and a check of the stored
“even” parity of the EPROM trim register. Failure of any of
these monitoring functions will result in the STATUS
input being driven high.
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, prop er 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 perma nent damage.)
Rating Symbol Value Unit
Unpowered Acceleration (all axes) gshock 2000
0.5 ms duration g
In use g shocks powered or unpowered
Capable of < 5 ppm device failure rate Gshock in use < 100
any duration g
In use g shocks powered or unpowered
Capable of < 50 ppm device failure rate Gshock in use < 100 - 1500
0.6 ms duration g
Supply Voltage VDD –0.3 to +7.0 V
Storage Temperature Range Tstg –40 to +125 °C
This is a mechanical shock sensitive device, improper handling can cause permanent damage to the part or
cause the part to otherwise fail.
Document Number: MMA2241KEG
Sensors
Freescale Semiconductor, Inc. 3
Table 2. Operating Characteristics
(Unless otherwise noted: –40°C TA +125°C, 4.75 VDD 5.25, Acceleration = 0g, Loaded output.(1))
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.
Characteristic Symbol Min Typ Max Unit
Operating Range(2)
Supply Voltage(3)
Supply Current
Operating Temperature Range
Acceleration Range
2. These limits define the range of operation for which the part will meet specification.
3. Within the supply range of 4.75 V and 5.25 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 guar anteed to be in calibration.
VDD
IDD
TA
gFS
4.75
4.0
40
—
5.00
5.0
—
10
5.25
6.0
+125
—
V
mA
C
g
Output Signal
Zero-g (TA = 25°C, VDD = 5.0 V)(4)
Zero-g
Sensitivity (TA = 25°C, VDD = 5.0 V)(5)
Sensitivity
Bandwidth Response
Nonlinearity
4. 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 and for negative acceleration the output will decrease below VDD/2.
5. The device is calibrated at 5g.
VOFF
VOFF,V
S
SV
f–3dB
NLOUT
2.30
0.46 VD
194.0
37.2
360
–1.0
2.500
0.50 VDD
200.0
40.0
400
—
2.70
0.54 VDD
206.0
42.8
440
+1.0
V
V
mV/g
mV/g/V
Hz
% FSO
Noise
RMS (10 Hz – 1 kHz) nRMS —3.5 5.0 mVrms
Self-Test
Output Response(6)
Input Low
Input High
Input Loading(7)
Response Time(8)
6. VOFF calculated with typical sensitivity.
7. The digital input pin has an internal pull-down current source to prevent inadvertent self test initiation due to external board level leakages.
8. Time for the output to reach 90% of its final value after a self-test is initiated.
gST
VIL
VIH
IIN
tST
4.0
VSS
0.7 xVDD
–30
—
5.0
—
—
–100
2.0
6.0
0.3 x VDD
VDD
–300
10
g
V
V
A
ms
Status(9), (10)
Output Low (Iload = 100 A)
Output High (Iload = 100 A)
9. 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.
10. The S t atus 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.
VOL
VOH
—
VDD –0.8 —
—0.4
—V
V
Minimum Supply Voltage (LVD Trip) VLVD 2.7 3.25 4.0 V
Clock Monitor Fail Detection Frequency fmin 150 —400 kHz
Output Stage Performance
Electrical Saturation Recovery Time(11)
Full Scale Output Range (IOUT = 200 A)
Capacitive Load Drive(12)
Output Impedance
11. Time for amplifiers to recover after an ac celeration signal causing them to saturate.
12. Preserves phase margin (60°) to guarantee output amplifier stability.
tDELAY
VFSO
CL
ZO
—
0.25
—
—
0.2
—
—
300
—
VDD –0.25
100
—
ms
V
pF
Mechanical Characteristics
Transverse Sensitivity(13)
Package Resonance
13. A measure of the device's ability to reject an acceleration applied 90° from the true axis of sensitivity.
VXZ,YZ
fPKG
—
——
10 5.0
—% FSO
kHz
Document Number: MMA2241KEG
Sensors
4Freescale Semiconductor, Inc.
PRINCIPLE OF OPERATION
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 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 semiconducto r
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.
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 shap e 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 al lows 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 . Th e resulting electrostatic
force causes the center plate to deflect.
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 fu nctioning.
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.
Acceleration
Figure 3. Transducer
Physical Model Figure 4. Equivalent
Circuit Model
Fe1
2
---AV2
d2
------=



Document Number: MMA2241KEG
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Freescale Semiconductor, Inc. 5
BASIC CONNECTIONS
Pinout Description
Figure 4. SOIC Accelerometer with Recommended
Terminations
PCB Layout
Figure 5. Recommended PCB Layout for Interfacing
Accelerometer to Microcontroller
NOTES:
1. Use a 0.1 F capacitor on VDD to decouple the power
source.
2. Physical coupling distance of the accelerometer to the
microcontro l l er should be minimal.
3. Place a ground plane ben eath the accelerometer to
reduce noise, the ground plane should be attached to
all of the open ended terminals shown in Figure 5.
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).
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. This wil l prevent aliasing errors.
Table 3. Pin Descriptions
Pin No. Pin Name Description
1 thru 3 —No internal connection. Leave
unconnected.
4ST Logic input pin used to initiate
self-test.
5 VOUT Output voltage of the
accelerometer.
6STATUS Logic output pin to indicate fault.
7 VSS The power supply ground.
8 VDD The power supply input.
9 thru 13 Trim pins Used for factory trim. Leave
unconnected.
14 thru 16 —No internal connection. Leave
unconnected.
N/C
N/C
N/C
ST
VOUT
STATUS
VSS
VDD
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
MMA2241KEG
ST
VOUT Output
Signal
R1
1 k
5
C2
0.01 F
4
7
Logic
Input
VDD
C1
0.1 F
6STATUS
8VDD
VSS
P0
A/D In
VRH
VSS
VDD
ST
VOUT
VSS
VDD
0.01 F1 k
0.1 F
0.1 F
Power Supply
0.1 F
P1STATUS
Microcontroller
Accelerometer
C
C
C
R
C
Document Number: MMA2241KEG
Sensors
6Freescale Semiconductor, Inc.
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
–x
Direction of Earth’s gravity field(1)
1. When positioned as shown, the Earth’s gravity will result in a positive 1g output.
87654321
910111213141516
+x
16-Pin SOIC Package
N/C pins are recommended to be left FLOATING
Front View Side View
Top View
Acceleration of the package in the
X direction (center plate moves in
the X direction) will result in an
increase in the output.
Dynamic Acceleration Sensing Direction
Static Acceleration Sensing Direction
Activation of Self Test moves the
center plate in the X direction,
resulting in an increase in the
output.
Document Number: MMA2241KEG
Sensors
Freescale Semiconductor, Inc. 7
MINIMUM RECOMMENDED FOOTPRINT FOR SURFACE MOUNTED APPLICATIONS
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 bridgi ng and
shorting between solder pads.
Figure 6. Footprint SOIC-16 (Case 475-01)
Document Number: MMA2241KEG
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8Freescale Semiconductor, Inc.
PACKAGE DIMENSIONS
CASE 475-01
ISSUE C
16-LEAD SOIC
PAGE 1 OF 2
Document Number: MMA2241KEG
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Freescale Semiconductor, Inc. 9
PACKAGE DIMENSIONS
CASE 475-01
ISSUE C
16-LEAD SOIC
PAGE 2 OF 2
Table 4. Revision History
Revision
number Revision
date Descriptio n of changes
3 11/2012 • Table 2. Operating Characteristics, added footnote f or Self-Test Output Response, updated page
4: Principle of Op eration
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© 2012 Freescale Semiconductor, Inc.
Document Number: MMA2241KEG
Rev. 3
11/2012