MOTOROLA
SEMICONDUCTOR TECHNICAL DATA
Micromachined Accelerometer
The MMA series of silicon capacitive, micromachined accelerometers
features 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
•
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
•
Two Packaging Options Available:
1) Plastic DIP for Z Axis Sensing (MMA1201P)
2) Wingback for X Axis Sensing (MMA2200W)
Typical Applications
•
Vibration Monitoring and Recording
•
Appliance Control
•
Mechanical Bearing Monitoring
•
Computer Hard Drive Protection
•
Computer Mouse and Joysticks
•
Virtual Reality Input Devices
•
Sports Diagnostic Devices and Systems
MMA1201P
MMA2200W
MMA1201P: Z AXIS SENSITIVITY
MMA2200W: X AXIS SENSITIVITY
MICROMACHINED
ACCELEROMETER
±
40g
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
DIP PACKAGE
CASE 648C
MMA1201P
12
3
4
5
6
WB PACKAGE
CASE 456
MMA2200W
SIMPLIFIED ACCELEROMETER FUNCTIONAL BLOCK DIAGRAM
VDD
G–CELL
SENSOR
INTEGRATOR
GAIN
FILTER
TEMP
COMP
VOUT
VST
SELF–TEST
CONTROL LOGIC &
EPROM TRIM CIRCUITS
OSCILLATOR
CLOCK GEN.
VSS
STATUS
Figure 1. Simplified Accelerometer Functional Block Diagram
REV 0
2–12
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Motorola Sensor Device Data
MMA1201P MMA2200W
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
Gpd
Gupd
VDD
Ddrop
Tstg
Value
500
2000
–0.3 to +7.0
1.2
– 40 to +105
Unit
g
g
V
m
°C
ELECTRO STATIC DISCHARGE (ESD)
WARNING: This device is sensitive to electrostatic
discharge.
Although the Motorola 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 per-
formance 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.
Motorola Sensor Device Data
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2–13
MMA1201P MMA2200W
OPERATING CHARACTERISTICS
(Unless otherwise noted: –40°C
v
TA
v
+85°C, 4.75
v
VDD
v
5.25, Acceleration = 0g, Loaded output(1))
Symbol
VDD
IDD
TA
gFS
VOFF
VOFF,V
S
SV
f –3dB
NLOUT
nRMS
nPSD
nCLK
gST
VIL
VIH
IIN
tST
VOL
VOH
VLVD
fmin
tDELAY
VFSO
CL
ZO
VZX,YX
fPKG
Min
4.75
4.0
40
—
Typ
5.00
5.0
—
38
2.5
0.50 VDD
50
10
400
—
—
110
2.0
—
—
—
110
2.0
—
—
3.25
—
0.2
—
—
300
—
10
Max
5.25
6.0
+85
—
2.8
0.56 VDD
52.5
10.7
440
+1.0
3.5
—
—
30
0.3 x VDD
VDD
300
10
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
Ω
% FSO
kHz
Characteristic
Operating Range(2)
Supply Voltage(3)
Supply Current
Operating Temperature Range
Acceleration Range
Output Signal
Zero g (VDD = 5.0 V)(4)
Zero g
Sensitivity (TA = 25°C, VDD = 5.0 V)(5)
Sensitivity (VDD = 5.0 V)
Bandwidth Response
Nonlinearity
Noise
RMS (.01–1 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(12)(13)
Output Low (Iload = 100
µA)
Output High (Iload = 100
µA)
Minimum Supply Voltage (LVD Trip)
Clock Monitor Fail Detection Frequency
Output Stage Performance
Electrical Saturation Recovery Time(9)
Full Scale Output Range (IOUT = 200
µA)
Capacitive Load Drive(10)
Output Impedance
Mechanical Characteristics
Transverse Sensitivity(11)
Package Resonance
*
2.2
0.44 VDD
47.5
9.3
360
1.0
*
—
—
—
20
VSS
0.7 x VDD
30
—
*
*
*
—
VDD
*
.8
0.4
—
4.0
260
—
2.7
50
—
0.3
—
—
—
—
VDD 0.3
100
—
5.0
—
*
NOTES:
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 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 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 20g.
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. Time for amplifiers to recover after an acceleration signal causing them to saturate.
10. Preserves phase margin (60°) to guarantee output amplifier stability.
11. A measure of the device’s ability to reject an acceleration applied 90° from the true axis of sensitivity.
12. 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.
13. 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 by a rising edge on self–test, unless a fault condition continues to exist.
*
^
2–14
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Motorola Sensor Device Data
MMA1201P MMA2200W
PRINCIPLE OF OPERATION
The Motorola accelerometer is a surface–micromachined
integrated–circuit accelerometer.
The device consists of a surface micromachined capaci-
tive 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 semicon-
ductor materials (polysilicon) using semiconductor pro-
cesses (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 sub-
jecting the system to an acceleration (Figure 2).
When the center plate deflects, the distance from it to one
fixed plate will increase by the same amount that the dis-
tance 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 3). 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 ratio-
metric and proportional to acceleration.
Acceleration
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 elec-
trostatic force (Fe = 1/2 AV2/d2) causes the center plate to
deflect. The resultant deflection is measured by the accel-
erometer’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
Motorola 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 rising edge on the self–
test input pin, unless one (or more) of the fault conditions
continues to exist.
BASIC CONNECTIONS
Pinout Description for the Wingback Package
Figure 2. Transducer
Physical Model
Figure 3. Equivalent
Circuit Model
12
3
4
5
SPECIAL FEATURES
Filtering
The Motorola accelerometers contain an onboard 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 fil-
ter 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
Pin No.
1
2
3
4
5
6
—
Pin Name
—
ST
VOUT
Status
VSS
VDD
Wings
6
Description
Leave unconnected or connect to sig-
nal ground
Logic input pin to initiate self test
Output voltage
Logic output pin to indicate fault
Signal ground
Supply voltage (5 V)
Support pins, internally connected to
lead frame. Tie to VSS.
Motorola Sensor Device Data
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2–15
MMA1201P MMA2200W
VDD
MMA2200W
LOGIC
INPUT
2 ST
6 VDD
C1
0.1
µF
5 VSS
VOUT
3
4
R1
1 kΩ
STATUS
VDD
MMA1201P
LOGIC
INPUT
4 ST
8 VDD
C1
0.1
µF
7 VSS
VOUT
5
6
R1
1 kΩ
STATUS
OUTPUT
SIGNAL
OUTPUT
SIGNAL
C2
0.01
µF
C2
0.01
µF
Figure 4. Wingback Accelerometer with
Recommended Connection Diagram
Figure 5. DIP Accelerometer with Recommended
Connection Diagram
PCB Layout
STATUS
ACCELEROMETER
ST
VOUT
VSS
VDD
R
1 kΩ
C 0.1
µF
VRH
C
0.1
µF
C 0.01
µF
P1
MICROCONTROLLER
P0
A/D IN
Pinout Description for the DIP Package
N/C
N/C
N/C
ST
VOUT
STATUS
VSS
VDD
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
VSS
C 0.1
µF
VDD
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
POWER SUPPLY
Figure 6. Recommend PCB Layout for Interfacing
Accelerometer to Microcontroller
NOTES:
•
Use a 0.1
µF
capacitor on VDD 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 kΩ and 0.01
µF
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 inter-
fere with the internal accelerometer sampling frequency.
This will prevent aliasing errors.
Pin No.
1
2 thru 3
4
5
6
7
8
9 thru 13
14 thru 16
Pin Name
—
—
ST
VOUT
Status
VSS
VDD
Trim Pins
—
Description
Leave unconnected or connect to
signal ground.
No internal connection. Leave un-
connected.
Logic input pin to initiate self test.
Output voltage
Logic output pin to indicate fault.
Signal ground
Supply voltage (5 V)
Used for factory trim. Leave un-
connected.
No internal connection. Leave un-
connected.
2–16
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Motorola Sensor Device Data
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