Freescale Semiconductor
Technical Data
Document Number: MMA7261QT
Rev 3, 09/2007
±2.5g
- 10g Three Axis Low-g
Micromachined Accelerometer
The MMA7261QT low cost capacitive micromachined accelerometer
features signal conditioning, a 1-pole low pass filter, temperature
compensation and g-Select which allows for the selection among 4
sensitivities. Zero-g offset full scale span and filter cut-off are factory set and
require no external devices. Includes a Sleep Mode that makes it ideal for
handheld battery powered electronics.
Features
•
•
•
•
•
•
•
•
•
•
•
Selectable Sensitivity (2.5g/3.3g/6.7g/10g)
Low Current Consumption: 500
μA
Sleep Mode: 3
μA
Low Voltage Operation: 2.2 V – 3.6 V
6mm x 6mm x 1.45mm QFN
Fast Turn On Time
High Sensitivity (2.5 g)
Integral Signal Conditioning with Low Pass Filter
Robust Design, High Shocks Survivability
Environmentally Preferred Package
Low Cost
MMA7261QT
MMA7261QT: XYZ AXIS
ACCELEROMETER
±2.5g/3.3g/6.7g/10g
Bottom View
Typical Applications
•
•
•
•
•
•
•
•
HDD MP3 Player: Freefall Detection
Laptop PC: Freefall Detection, Anti-Theft
Cell Phone: Image Stability, Text Scroll, Motion Dialing, E-Compass
Pedometer: Motion Sensing
PDA: Text Scroll
Navigation and Dead Reckoning: E-Compass Tilt Compensation
Gaming: Tilt and Motion Sensing, Event Recorder
Robotics: Motion Sensing
ORDERING INFORMATION
Device Name
MMA7261QT
MMA7261QR2
Temperature
Range
– 40 to +105°C
– 40 to +105°C
Package
Drawing
1622-02
1622-02
Package
QFN-16, Tray
QFN-16,Tape & Reel
g-Select1 1
g-Select2 2
V
DD
3
V
SS
4
16-LEAD
QFN
CASE 1622-02
Top View
X
OUT
Y
OUT
Z
OUT
N/C
16 15
14 13
12
Sleep
Mode
11 N/C
10 N/C
9 N/C
5
N/C
6
N/C
7
N/C
8
N/C
Figure 1. Pin Connections
© Freescale Semiconductor, Inc., 2005-2007. All rights reserved.
V
DD
g-Select1
g-Select2
Oscillator
Clock
Generator
X-Temp
Comp
X
OUT
Sleep Mode
G-Cell
Sensor
C to V
Converter
Gain
+
Filter
Y-Temp
Comp
Y
OUT
Control Logic
EEPROM Trim Circuits
Z-Temp
Comp
Z
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
±2000
–0.3 to +3.6
1.8
–40 to +125
Unit
g
V
m
°C
ELECTRO STATIC DISCHARGE (ESD)
WARNING: This device is sensitive to electrostatic
discharge.
Although the Freescale accelerometer contains internal
2000 V 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.
MMA7261QT
2
Sensors
Freescale Semiconductor
Table 2. Operating Characteristics
Unless otherwise noted: –40°C < T
A
< 105°C, 2.2 V < V
DD
< 3.6 V, Acceleration = 0g, Loaded output
(1)
Characteristic
Operating Range
(2)
Supply Voltage
(3)
Supply Current
Supply Current at Sleep Mode
(4)
Operating Temperature Range
Acceleration Range, X-Axis, Y-Axis, Z-Axis
g-Select1 & 2: 00
g-Select1 & 2: 10
g-Select1 & 2: 01
g-Select1 & 2: 11
Output Signal
Zero-g (T
A
= 25°C, V
DD
= 3.3 V)
(5)
Zero-g
(4)
X-axis
Y-axis
Z-axis
Sensitivity (T
A
= 25°C, V
DD
= 3.3 V)
2.5g
3.3g
6.7g
10g
Sensitivity
(4)
X-axis
Y-axis
Z-axis
Bandwidth Response
XY
Z
Noise
RMS (0.1 Hz – 1 kHz)
(4)
Power Spectral Density RMS (0.1 Hz – 1 kHz)
(4)
Control Timing
Power-Up Response Time
(8)
Enable Response Time
(9)
Sensing Element Resonant Frequency
XY
Z
Internal Sampling Frequency
Output Stage Performance
Full-Scale Output Range (I
OUT
= 30 µA)
Nonlinearity, X
OUT
, Y
OUT
, Z
OUT
Cross-Axis Sensitivity
(10)
Symbol
Min
Typ
Max
Unit
V
DD
I
DD
I
DD
T
A
g
FS
g
FS
g
FS
g
FS
2.2
—
—
-40
—
—
—
—
3.3
500
3
—
±2.5
±3.3
±6.7
±10.0
3.6
800
10
+105
—
—
—
—
V
μA
μA
°C
g
g
g
g
V
OFF
V
OFF
, T
A
V
OFF
, T
A
V
OFF
, T
A
S
2.5g
S
3.3g
S
6.7g
S
10g
S,T
A
S,T
A
S,T
A
f
-3dB
f
-3dB
1.485
-0.5
(6)
-4.2
(6)
-2.5
(6)
444
333
167
111
±0.02
(6)
±0.01
(6)
±0.01
(6)
—
—
1.65
-4.5
-6.2
-3.1
480
360
180
120
±0.02
±0.01
±0.00
350
150
1.815
-7.0
(7)
-6.9
(7)
-3.8
(7)
516
387
193
129
±0.02
(7)
±0.01
(7)
±0.01
(7)
—
—
V
mg/°C
mg/°C
mg/°C
mV/g
mV/g
mV/g
mV/g
%/°C
%/°C
%/°C
Hz
Hz
n
RMS
n
PSD
t
RESPONSE
t
ENABLE
f
GCELL
f
GCELL
f
CLK
—
—
4.7
350
—
—
mVrms
μg/
Hz
ms
ms
kHz
kHz
kHz
—
—
—
—
—
1.0
0.5
6.0
3.4
11
2.0
2.0
—
—
—
V
FSO
NL
OUT
V
XY, XZ, YZ
V
SS
+0.25
–1.0
—
—
—
—
V
DD
–0.25
+1.0
5.0
V
%FSO
%
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 on V
DD
-GND.
2. These limits define the range of operation for which the part will meet specification.
3. Within the supply range of 2.2 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. This value is measured with g-Select in 2.5g mode.
5. 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.
6.These values represent the 10th percentile, not the minimum.
7.These values represent the 90th percentile, not the maximum.
8. The response time between 10% of full scale V
DD
input voltage and 90% of the final operating output voltage.
9. The response time between 10% of full scale Sleep Mode input voltage and 90% of the final operating output voltage.
10. A measure of the device’s ability to reject an acceleration applied 90° from the true axis of sensitivity.
MMA7261QT
Sensors
Freescale Semiconductor
3
PRINCIPLE OF OPERATION
The Freescale accelerometer is a surface-micromachined
integrated-circuit accelerometer.
The device consists of two surface micromachined
capacitive sensing cells (g-cell) and a signal conditioning
ASIC contained in a single integrated circuit package. The
sensing elements are sealed hermetically at the wafer level
using a bulk micromachined cap wafer.
The g-cell is a mechanical structure formed from
semiconductor materials (postillion) using semiconductor
processes (masking and etching). It can be modeled as a set
of beams attached to a movable central mass that move
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 beams form two back-to-back capacitors
(Figure
3).
As the center beam moves with acceleration, the
distance between the beams changes and each capacitor's
value will change, (C = Aε/D). Where A is the area of the
beam,
ε
is the dielectric constant, and D is the distance
between the beams.
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.
Acceleration
SPECIAL FEATURES
g-Select
The g-Select feature allows for the selection among 4
sensitivities present in the device. Depending on the logic
input placed on pins 1 and 2, the device internal gain will be
changed allowing it to function with a 2.5g, 3.3g, 6.7g, or 10g
sensitivity (Table
3).
This feature is ideal when a product has
applications requiring different sensitivities for optimum
performance. The sensitivity can be changed at anytime
during the operation of the product. The g-Select1 and g-
Select2 pins can be left unconnected for applications
requiring only a 2.5g sensitivity as the device has an internal
pull-down to keep it at that sensitivity (480mV/g).
Table 3. g-Select pin Descriptions
g-Select2
0
0
1
1
g-Select1
0
1
0
1
g-Range
2.5g
3.3g
6.7g
10g
Sensitivity
480mV/g
360mV/g
180mV/g
120mV/g
Sleep Mode
The 3 axis accelerometer provides a Sleep Mode that is
ideal for battery operated products. When Sleep Mode is
active, the device outputs are turned off, providing significant
reduction of operating current. A low input signal on pin 12
(Sleep Mode) will place the device in this mode and reduce
the current to 3uA typ. For lower power consumption, it is
recommended to set g-Select1 and g-Select2 to 2.5g mode.
By placing a high input signal on pin 12, the device will
resume to normal mode of operation.
Filtering
The 3 axis accelerometer contains onboard single-pole
switched capacitor filters. 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.
Figure 3. Simplified Transducer Physical Model
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.
MMA7261QT
4
Sensors
Freescale Semiconductor
BASIC CONNECTIONS
Pin Descriptions
Top View
X
OUT
Y
OUT
N/C
N/C
POWER SUPPLY
PCB Layout
16 15
g-Select1
g-Select2
V
DD
V
SS
1
2
3
4
5
N/C
6
N/C
14 13
12
11
10
9
7
N/C
8
N/C
Sleep Mode
N/C
Accelerometer
N/C
N/C
V
DD
V
SS
Sleep Mode
g-Select1
g-Select2
X
OUT
Y
OUT
Z
OUT
R
C
R
C
R
C
C
C
V
RH
P0
P1
P2
A/D
IN
A/D
IN
A/D
IN
Microcontroller
V
DD
V
SS
C
Figure 4. Pinout Description
Table 4. Pin Descriptions
Pin No.
1
2
3
4
5-7
8 - 11
12
13
14
15
16
Pin Name
g-Select1
g-Select2
V
DD
V
SS
N/C
N/C
Sleep Mode
Z
OUT
Y
OUT
X
OUT
N/C
Description
Logic input pin to select g level.
Logic input pin to select g level.
Power Supply Input
Power Supply Ground
No internal connection.
Leave unconnected.
Unused for factory trim.
Leave unconnected.
Logic input pin to enable product or
Sleep Mode.
Z direction output voltage.
Y direction output voltage.
X direction output voltage.
No internal connection.
Leave unconnected.
Figure 6. Recommended PCB Layout for Interfacing
Accelerometer to Microcontroller
NOTES:
1. Use 0.1 µF capacitor on V
DD
to decouple the power
source. Do not exceed capacitor values of 2.2 or
3.3 µF. Slow dV/dt rise times on V
DD
may cause the
device to not power up below 0
°
C.To ensure
operation below 0
°
C ensure V
DD
line has the ability
to reach 2.2V in < 0.1 ms as measured on the device
at the V
DD
pin. If output signal does not assert itself,
then the dv/dt at the V
DD
pin of the device should be
measured.
2. Physical coupling distance of the accelerometer to
the microcontroller should be minimal.
3. The flag underneath the package is internally
connected to ground. It is not recommended for the
flag to be soldered down.
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.
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 (11 kHz 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.
MMA7261QT
Logic
Inputs
1
g-Select1
Z
OUT
13
1 kΩ
0.1
μF
V
DD
2 g-Select2
MMA7261QT
3
V
DD
Y
OUT
14
1 kΩ
0.1
μF
0.1
μF
4
V
SS
X
OUT
15
Sleep Mode
1 kΩ
0.1
μF
12
Logic
Input
Figure 5. Accelerometer with Recommended
Connection Diagram
Sensors
Freescale Semiconductor
5
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