Freescale Semiconductor
Technical Data
Document Number: MMA6231Q
Rev 2, 10/2006
±10g
Dual Axis
Micromachined Accelerometer
The MMA6200 series of low cost capacitive micromachined accelerometers
feature signal conditioning, a 1-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
•
•
•
•
•
•
•
•
•
•
Low Noise
Low Cost
Low Power
2.7 V to 3.6 V Operation
6mm x 6mm x 1.98 mm QFN
Integral Signal Conditioning with Low Pass Filter
Linear Output
Ratiometric Performance
Self-Test
Robust Design, High Shocks Survivability
MMA6231Q
MMA6233Q
MMA6230Q Series: X-Y AXIS
SENSITIVITY MICROMACHINED
ACCELEROMETER
±10
g
Bottom View
Typical Applications
•
•
•
•
•
•
•
Pedometer
Appliance Control
Impact Monitoring
Vibration Monitoring and Recording
Position & Motion Sensing
Freefall Detection
Smart Portable Electronics
16-LEAD
QFN
CASE 1477-02
Top View
X
OUT
Y
OUT
N/C
ORDERING INFORMATION
Device Name
MMA6231Q
MMA6231QR2
MMA6233Q
MMA6233QR2
Bandwidth
Response
300 Hz
300 Hz
900 Hz
900 Hz
NC
1
2
3
4
16 15
14 13
12 ST
11 N/C
10 N/C
9 N/C
I
DD
1.2 mA
1.2 mA
2.2 mA
2.2 mA
Case No.
1477-02
1477-02
1477-02
1477-02
Package
QFN-16, Tube
QFN-16,Tape & Reel
QFN-16, Tube
QFN-16,Tape & Reel
NC
V
DD
V
SS
5
N/C
6
N/C
7
N/C
Figure 1. Pin Connections
© Freescale Semiconductor, Inc., 2006. All rights reserved.
N/C
N/C
8
G-Cell
Sensor
X-Integrator
X-Gain
X-Filter
X-Temp
Comp
V
DD
X
OUT
ST
Self Test
Control Logic &
EEPROM Trim Circuits
Oscillator
Clock Generator
Y-Integrator
Y-Gain
Y-Filter
Y-Temp
Comp
Y
OUT
V
SS
Figure 2. Simplified Accelerometer Functional Block Diagram
Table 1. Maximum Ratings
(Maximum ratings are the limits to which the device can be exposed without causing permanent damage.)
Rating
Maximum Acceleration (all axis)
Supply Voltage
Drop Test
(1)
Storage Temperature Range
1. Dropped onto concrete surface from any axis.
Symbol
g
max
V
DD
D
drop
T
stg
Value
Unit
g
V
m
°C
±
2000
–0.3 to +3.6
1.2
–40 to +125
ELECTRO STATIC DISCHARGE (ESD)
WARNING: This device is sensitive to electrostatic
discharge.
Although the Freescale accelerometers contain internal
2 kV 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.
MMA6231Q
2
Sensors
Freescale Semiconductor
Table 2. Operating Characteristics
Unless otherwise noted: -20°C < T
A
< 85°C, 3.0 V < V
DD
< 3.6 V, Acceleration = 0g, Loaded output
(1)
Characteristic
Operating Range
(2)
Supply Voltage
(3)
Supply Current
MMA6231Q
MMA6233Q
Operating Temperature Range
Acceleration Range
Output Signal
Zero g (T
A
= 25°C, V
DD
= 3.3 V)
(4)
Zero g
Sensitivity (T
A
= 25°C, V
DD
= 3.3 V)
Sensitivity
Bandwidth Response
MMA6231Q
MMA6233Q
Nonlinearity
Noise
MMA6231Q RMS (0.1 Hz – 1 kHz)
MMA6233Q RMS (0.1 Hz – 1 kHz)
Power Spectral Density RMS (0.1 Hz – 1 kHz)
MMA6231Q
MMA6233Q
Self-Test
Output Response
Input Low
Input High
Pull-Down Resistance
(5)
Response
Time
(6)
Output Stage Performance
Full-Scale Output Range (I
OUT
= 200 µA)
Capacitive Load
Drive
(7)
Output Impedance
Power-Up Response Time
MMA6231Q
MMA6233Q
Mechanical Characteristics
Transverse Sensitivity
(8)
V
ZX
,
YX
,
ZY
–5.0
—
+5.0
% FSO
t
RESPONSE
t
RESPONSE
—
—
2.0
0.7
—
—
ms
ms
V
FSO
C
L
Z
O
V
SS
+0.25
—
—
—
—
50
V
DD
–0.25
100
300
V
pF
Ω
g
ST
V
IL
V
IH
R
PO
t
ST
2.0
—
0.7 V
DD
43
—
—
—
—
57
2.0
—
0.3 V
DD
V
DD
71
—
g
V
V
kΩ
ms
n
PSD
n
PSD
—
—
50
30
—
—
ug/√Hz
n
RMS
n
RMS
—
—
0.7
0.6
—
—
mVrms
f
_3dB
f
_3dB
NL
OUT
—
—
–1.0
300
900
—
—
—
+1.0
Hz
Hz
% FSO
V
OFF
V
OFF
, T
A
S
S, T
A
1.485
—
111
—
1.65
2.0
120
0.015
1.815
—
129
—
V
mg/°C
mV/g
%/°C
I
DD
I
DD
T
A
g
FS
—
—
–20
—
1.2
2.2
—
10
1.5
3.0
+85
—
mA
mA
°C
g
V
DD
2.7
3.3
3.6
V
Symbol
Min
Typ
Max
Unit
1. For a loaded output, the measurements are observed after an RC filter consisting of a 1.0 kΩ resistor and a 0.1 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 2.7 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. The device can measure both + and – acceleration. With no input acceleration the output is at midsupply. For positive acceleration the output
will increase above V
DD
/2. For negative acceleration, the output will decrease below V
DD
/2.
5. The digital input pin has an internal pull-down resistance to prevent inadvertent self-test initiation due to external board level leakages.
6. Time for the output to reach 90% of its final value after a self-test is initiated.
7. Preserves phase margin (60°) to guarantee output amplifier stability.
8. A measure of the device’s ability to reject an acceleration applied 90° from the true axis of sensitivity.
MMA6231Q
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 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 a set
of beams attached to a movable central mass that moves
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 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 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
These Freescale accelerometers contain 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.
Self-Test
The sensor provides a self-test feature allowing the
verification of the mechanical and electrical integrity of the
accelerometer at any time before or after installation. A fourth
plate
is used in the g-cell as a self-test plate. When a logic
high input to the self-test pin is applied, 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 ASIC and a proportional output
voltage results. This procedure assures both the mechanical
(g-cell) and electronic sections of the accelerometer are
functioning.
Freescale accelerometers include fault detection circuitry
and a fault latch. Parity of the EEPROM bits becomes odd in
number.
Self-test is disabled when EEPROM parity error occurs.
Ratiometricity
Ratiometricity simply means the output offset voltage 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
Figure 3. Transducer
Physical Model
Figure 4. Equivalent
Circuit Model
MMA6231Q
4
Sensors
Freescale Semiconductor
BASIC CONNECTIONS
Pinout Description
PCB Layout
Top View
X
OUT
Y
OUT
N/C
N/C
ST
Accelerometer
X
OUT
Y
OUT
V
SS
V
DD
R
1 kΩ
R
1 kΩ
C 0.1
µF
C
C
0.1
µF
P0
Microcontroller
A/D IN
A/D IN
0.1
µF
16 15
NC
NC
V
DD
V
SS
1
2
3
4
5
N/C
6
N/C
14 13
12 ST
11 N/C
10 N/C
9 N/C
7
N/C
8
N/C
V
SS
C 0.1
µF
V
DD
V
RH
C 0.1
µF
Figure 4. Pinout Description
Pin No.
1, 5–7, 13, 16
14
15
3
4
2, 8–11
12
Pin
Name
N/C
Y
OUT
X
OUT
V
DD
V
SS
N/C
ST
Description
No internal connection.
Leave unconnected.
Output voltage of the accelerometer.
Y Direction.
Output voltage of the accelerometer.
X Direction.
Power supply input.
The power supply ground.
Used for factory trim.
Leave unconnected.
Logic input pin used to initiate
self-test.
Power Supply
Figure 6. Recommend PCB Layout for Interfacing
Accelerometer to Microcontroller
NOTES:
1. Use 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. Flag underneath package is connected to ground.
4. 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.
5. Use an RC filter with 1.0 kΩ and 0.1 µF on the outputs
of the accelerometer to minimize clock noise (from the
switched capacitor filter circuit).
6. PCB layout of power and ground should not couple
power supply noise.
V
DD
3
0.1
µF
4
12
V
SS
V
DD
MMA6200Q
Series
Y
OUT
14
1 kΩ
0.1
µF
X Output
Signal
7. Accelerometer and microcontroller should not be a
high current path.
8. 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 (16 kHz for Low I
DD
and 52 kHz for
Standard I
DD
for the sampling frequency). This will
prevent aliasing errors.
9. PCB layout should not run traces or vias under the
QFN part. This could lead to ground shorting to the
accelerometer flag.
Logic
Input
X
OUT
15
ST
1 kΩ
0.1
µF
Y Output
Signal
Figure 5. Accelerometer with Recommended
Connection Diagram
MMA6231Q
Sensors
Freescale Semiconductor
5
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