Freescale Semiconductor
Technical Data
MMA1260D
Rev. 1, 10/2004
Low G
Micromachined Accelerometer
The MMA series of silicon capacitive, micromachined accelerometers
features 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
•
2nd Order Bessel Filter
•
Calibrated Self--test
•
EPROM Parity Check Status
•
Transducer Hermetically Sealed at Wafer Level for Superior Reliability
•
Robust Design, High Shock Survivability
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
MMA1260D
MMA1260D: Z AXIS SENSITIVITY
MICROMACHINED
ACCELEROMETER
±1.5g
16
9
1
8
16 LEAD SOIC
CASE 475--01
Pin Assignment
V
SS
V
SS
V
SS
V
OUT
STATUS
V
DD
V
SS
ST
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
ORDERING INFORMATION
Device
MMA1260D
Temperature Range
--40 to +105°C
Case No.
Case 475--01
Package
SOIC--16
SIMPLIFIED ACCELEROMETER FUNCTIONAL BLOCK DIAGRAM
V
DD
G--CELL
SENSOR
INTEGRATOR
GAIN
FILTER
TEMP COMP
& GAIN
V
OUT
ST
SELF--TEST
CONTROL LOGIC &
EPROM TRIM CIRCUITS
OSCILLATOR
CLOCK GEN.
V
SS
STATUS
Figure 1. Simplified Accelerometer Functional Block Diagram
REV 1
©
Freescale Semiconductor, Inc., 2004. All rights reserved.
MMA1260D
1
Sensor Device Data
Freescale Semiconductor
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
g
pd
g
upd
V
DD
H
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 Semiconductor accelerometers
contain internal 2kV ESD protection circuitry, extra precau-
tion 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 magni-
tude 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 dis-
charges which may be detrimental to its performance.
MMA1260D
2
Sensor Device Data
Freescale Semiconductor
(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 (V
DD
= 5.0 V)
Sensitivity (T
A
= 25°C, V
DD
= 5.0 V)
(5)
Sensitivity (V
DD
= 5.0 V)
Bandwidth Response
Nonlinearity
Noise
RMS (0.1 Hz -- 1.0 kHz)
Spectral Density (RMS, 0.1 Hz -- 1.0 kHz)
(6)
Self--Test
Output Response (V
DD
= 5.0 V)
Input Low
Input High
Input Loading
(7)
Response Time
(8)
Status
(12)(13)
Output Low (I
load
= 100
µA)
Output High (I
load
= --100
µA)
Output Stage Performance
Electrical Saturation Recovery Time
(9)
Full Scale Output Range (I
OUT
= --200
µA)
Capacitive Load Drive
(10)
Output Impedance
Mechanical Characteristics
Transverse Sensitivity
(11)
Symbol
V
DD
I
DD
T
A
g
FS
V
OFF
V
OFF
S
S
f
--3dB
NL
OUT
n
RMS
n
SD
∆V
ST
V
IL
V
IH
I
IN
t
ST
V
OL
V
OH
t
DELAY
V
FSO
C
L
Z
O
V
XZ,YZ
Min
4.75
1.1
−40
—
2.25
2.2
1140
1110
40
−1.0
—
—
0.3
V
SS
0.7 V
DD
−50
—
—
V
DD
−0.8
—
V
SS
+0.25
—
—
—
Typ
5.00
2.2
—
1.5
2.5
2.5
1200
1200
50
—
5.0
500
0.6
—
—
−125
10
—
—
—
—
—
50
—
Max
5.25
3.2
+105
—
2.75
2.8
1260
1290
60
+1.0
9.0
—
0.9
0.3 V
DD
V
DD
−300
25
0.4
—
2.0
V
DD
−0.25
100
—
5.0
Unit
V
mA
°C
g
V
V
mV/g
mV/g
Hz
% FSO
mVrms
µg/√Hz
V
V
V
µA
ms
V
V
ms
V
pF
Ω
% FSO
OPERATING CHARACTERISTICS
NOTES:
1. For a loaded output the measurements are observed after an RC filter consisting of a 1 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 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 V
DD
/2 and for negative acceleration the output will decrease below V
DD
/2.
5. Sensitivity limits apply to 0 Hz acceleration.
6. At clock frequency
≅
34 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 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.
MMA1260D
Sensor Device Data
Freescale Semiconductor
3
PRINCIPLE OF OPERATION
The Freescale Semiconductor 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 us-
ing 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 (Fig-
ure 3). As the center plate moves with acceleration, the dis-
tance 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 be-
tween 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
SPECIAL FEATURES
Filtering
The Freescale Semiconductor accelerometers contain an
onboard 2--pole switched capacitor filter. A Bessel imple-
mentation is used because it provides a maximally flat delay
response (linear phase) thus preserving pulse shape integri-
ty. 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 fre-
quency.
Self-
-Test
The sensor provides a self--test feature that allows the ver-
ification of the mechanical and electrical integrity of the ac-
celerometer at any time before or after installation. 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 cali-
brated 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 re-
sultant deflection is measured by the accelerometer’s control
ASIC and a proportional output voltage results. This proce-
dure assures that both the mechanical (g--cell) and electronic
sections of the accelerometer are functioning.
Status
Freescale Semiconductor accelerometers include fault
detection circuitry and a fault latch. The Status pin is an out-
put 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.
Figure 2. Transducer
Physical Model
Figure 3. Equivalent
Circuit Model
MMA1260D
4
Sensor Device Data
Freescale Semiconductor
BASIC CONNECTIONS
V
SS
V
SS
V
SS
V
OUT
STATUS
V
DD
V
SS
ST
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
PCB Layout
STATUS
ACCELEROMETER
ST
V
OUT
V
SS
V
DD
R
1 kΩ
C 0.1
µF
V
RH
C
0.1
µF
C 0.1
µF
P1
P0
A/D IN
MICROCONTROLLER
V
SS
C 0.1
µF
V
DD
Figure 4. Pinout Description
Pin No.
1 thru 3
4
5
6
7
8
9 thru 13
14 thru 16
Pin Name
V
SS
V
OUT
STATUS
V
DD
V
SS
ST
Trim pins
—
Description
Redundant connections to the internal
V
SS
and may be left unconnected.
Output voltage of the accelerometer.
Logic output pin used to indicate fault.
The power supply input.
The power supply ground.
Logic input pin used to initiate self--
test.
Used for factory trim.
Leave unconnected.
No internal connection.
Leave unconnected.
POWER SUPPLY
Figure 6. Recommended PCB Layout for Interfacing
Accelerometer to Microcontroller
NOTES:
•
Use a 0.1
µF
capacitor on V
DD
to decouple the power
source.
•
Physical coupling distance of the accelerometer to the mi-
crocontroller should be minimal.
•
Place a ground plane beneath the accelerometer to reduce
noise, the ground plane should be attached to all internal
V
SS
terminals shown in Figure 4.
STATUS
V
DD
MMA1260D
LOGIC
INPUT
8 ST
6 V
DD
5
R1
1 kΩ
V
OUT
4
C1
0.1
µF
7 V
SS
OUTPUT
SIGNAL
•
Use an RC filter of 1 kΩ and 0.1
µF
on the output of the ac-
celerometer 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.
C2
0.1
µF
Figure 5. SOIC Accelerometer with Recommended
Connection Diagram
MMA1260D
Sensor Device Data
Freescale Semiconductor
5
京公网安备 11010802033920号
EEWORLD
