Freescale Semiconductor
Technical Data
MMA1212D
Rev 4, 03/2006
Surface Mount
Micromachined Accelerometer
The MMA series of silicon capacitive, micromachined accelerometers feature
signal conditioning, a 4-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
4
th
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
MMA1212
MMA1212D: Z AXIS SENSITIVITY
MICROMACHINED
ACCELEROMETER
±200g
Functional Description
•
•
Vibration Monitoring and Recording
Impact Monitoring
D SUFFIX
EG SUFFIX (Pb-FREE)
16-LEAD SOIC
CASE 475-01
ORDERING INFORMATION
Device Name
MMA1212D
MMA1212DR2
MMA1212EG
MMA1212EGR2
Temperature Range
–40°
to 125°C
–40°
to 125°C
–40°
to 125°C
–40°
to 125°C
Case No.
475-01
475-01
475-01
475-01
Package
SOIC-16
SOIC16, Tape & Reel
SOIC-16
SOIC16, Tape & Reel
V
DD
G-Cell
Sensor
Integrator
Gain
Filter
Temp
Comp
V
OUT
N/C
N/C
N/C
ST
V
OUT
STATUS
V
SS
V
DD
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
ST
Self-test
Control Logic &
EPROM Trim Circuits
Oscillator
Clock
Generator
V
SS
STATUS
Figure 1. Simplified Accelerometer Functional Block Diagram
Figure 2. Pin Connections
© Freescale Semiconductor, Inc., 2006. 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
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.
MMA1212D
2
Sensors
Freescale Semiconductor
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
Output Signal
Zero g (T
A
= 25°C, V
DD
= 5.0 V)
(4)
Zero g
Sensitivity (T
A
= 25°C, V
DD
= 5.0 V)
(5)
Sensitivity
Bandwidth Response
Nonlinearity
Noise
RMS (0.1-1 kHz)
Power Spectral Density
Clock Noise (without RC load on output)
(6)
Self-Test
Output Response
Input Low
Input High
Input Loading
(7)
Response Time
(8)
Status
(9), (10)
Output Low (I
load
= 100
µA)
Output High (I
load
= 100
µA)
Minimum Supply Voltage (LVD Trip)
Clock Monitor Fail Detection Frequency
Output Stage Performance
Electrical Saturation Recovery Time
(11)
Full Scale Output Range (I
OUT
= 200
µA)
Capacitive Load Drive
(12)
Output Impedance
Mechanical Characteristics
Transverse Sensitivity
(13)
Package Resonance
Symbol
V
DD
I
DD
T
A
g
FS
V
OFF
V
OFF,V
S
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
3.0
–40
—
2.35
0.47V
DD
9.5
1.86
360
–2.0
—
—
—
55
V
SS
0.7
×
V
DD
–30
—
—
V
DD
–.8
2.7
50
—
0.25
—
—
—
—
Typ
5.00
—
—
225
2.5
0.50 V
DD
10
2
400
—
—
110
2.0
75
—
—
–100
2.0
—
—
3.25
—
0.2
—
—
300
—
10
Max
5.25
6.0
+125
—
2.65
0.53 V
DD
10.5
2.14
440
2.0
2.8
—
—
95
0.3
×
V
DD
V
DD
–260
10
0.4
—
4.0
260
—
V
DD
–0.25
100
—
5.0
—
Unit
V
mA
C
g
V
V
mV/g
mV/g/V
Hz
% FSO
mVrms
µV/(Hz
1/2
)
mVpk
g
V
V
µA
ms
V
V
V
kHz
ms
V
pF
W
% FSO
kHz
1. For a loaded output the measurements are observed after an RC filter consisting of a 1 kΩ resistor and a 0.01
µF
capacitor to ground.
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 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. 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 35g.
6. At clock frequency
≅70
kHz.
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.
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 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
µs,
unless a fault condition continues to exist.
11. Time for amplifiers to recover after an acceleration signal causes them to saturate.
12. Preserves phase margin (60°) to guarantee output amplifier stability.
13. A measure of the device's ability to reject an acceleration applied 90° from the true axis of sensitivity.
MMA1212D
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 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 (poly silicon) 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 = Aε/D). Where A is the area of the
plate,
ε
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 on board 4-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 air bag
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
force (Fe =
1
/
2
AV
2
/d
2
) 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 functioning.
Ratiometricity
Ratiometricity simply means that the output offset voltage
and sensitivity will scale linearly with applied supply voltage.
That is, as you increase supply voltage 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.
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 one (or
more) of the following events occur:
• Supply voltage falls below the Low Voltage Detect (LVD)
voltage threshold
• Clock oscillator falls below the clock monitor minimum
frequency
• Parity of the EPROM bits becomes odd in number.
The fault latch can be reset by a falling 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
MMA1212D
4
Sensors
Freescale Semiconductor
BASIC CONNECTIONS
Pinout Description
PCB Layout
N/C
N/C
N/C
ST
V
OUT
STATUS
V
SS
V
DD
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
STATUS
Accelerometer
ST
V
OUT
V
SS
V
DD
R
1 kΩ
C 0.1
µF
C 0.01
µF
P1
Microcontroller
P0
A/D In
V
SS
C 0.1
µF
V
DD
V
RH
C 0.1
µF
Table 3. Pin Descriptions
Pin No.
1 thru 3
4
5
6
7
8
9 thru 13
14 thru 16
Pin Name
—
ST
V
OUT
STATUS
V
SS
V
DD
Trim pins
—
Description
Leave unconnected
Logic input pin used to initiate self-test
Output voltage of the accelerometer
Logic output pin to indicate fault
The power supply ground
The power supply input
Used for factory trim. Leave
unconnected
No internal connection. Leave
unconnected
Power Supply
Figure 6. Recommended PCB Layout for Interfacing
Accelerometer to Microcontroller
NOTES:
1. Use a 0.1
µF
capacitor on V
DD
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 an RC filter of 1 kΩ and 0.01
µF
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.
V
DD
Logic
Input
4
MMA1212D
ST
V
OUT
6
R1
1 kΩ
STATUS
Output
Signal
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 will prevent aliasing errors.
8 V
DD
5
C1
0.1
µF
7 V
SS
C2
0.01
µF
Figure 5. SOIC Accelerometer with Recommended
Connection Diagram
MMA1212D
Sensors
Freescale Semiconductor
5
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