MMA1252 [FREESCALE]
Low-g Micromachined Accelerometer; 低g加速度计微机械
| 型号： | MMA1252 |
| 厂家： | 
Freescale |
| 描述： | Low-g Micromachined Accelerometer |
| 文件： | 总10页 (文件大小：133K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Document Number: MMA1252
Rev 1, 07/2012
Freescale Semiconductor
Data Sheet: Technical Data
Low-g
MMA1252
Micromachined Accelerometer
The MMA series of silicon capacitive, micromachined accelerometers feature
signal conditioning, a 2-pole low pass filter and temperature compensation.
Zero-g offset full scale span and filter cutoff 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
16-LEAD SOIC
Pb-FREE
CASE 475-01
EPROM Parity Check Status
Transducer Hermetically Sealed at Wafer Level for Superior Reliability
Robust Design, High Shock Survivability
Qualified AECQ100, Rev. F Grade 2 (-40C/ +105C)
Top View
Typical Applications
•
•
•
•
•
•
•
Vibration Monitoring and Recording
Appliance Control
16
15
14
13
12
11
10
9
VSS
VSS
VSS
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
1
2
3
4
5
6
7
8
Mechanical Bearing Monitoring
Computer Hard Drive Protection
Computer Mouse and Joysticks
Virtual Reality Input Devices
Sports Diagnostic Devices and Systems
VOUT
STATUS
VDD
VSS
ST
ORDERING INFORMATION
Pin Connections
Device Name
Temperature Range
–40to 105C
Case No.
475-01
475-01
475-01
475-01
Package
SOIC-16
MMA1252EG
MMA1252EGR2
MMA1252KEG*
MMA1252KEGR2*
–40to 105C
SOIC-16, Tape & Reel
SOIC-16
–40to 105C
–40to 105C
SOIC-16, Tape & Reel
*Part number sourced from a different facility.
© 2012 Freescale Semiconductor, Inc. All rights reserved.
VDD
Temp Comp
and Gain
G-Cell
Sensor
VOUT
Integrator
Gain
Filter
ST
Control Logic &
EPROM Trim Circuits
Clock
Generator
Oscillator
Self-test
VSS
STATUS
Figure 1 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
Symbol
Gpd
Value
1500
Unit
g
Powered Acceleration (all axes)
Unpowered Acceleration (all axes)
Supply Voltage
Gupd
VDD
2000
g
–0.3 to +7.0
1.2
V
Drop Test (1)
Ddrop
Tstg
m
Storage Temperature Range
–40 to +125
°C
1. Dropped onto concrete surface from any axis.
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.
MMA1252
Sensors
2
Freescale Semiconductor, Inc.
Table 2. Operating Characteristics
(Unless otherwise noted: –40°C TA +105°C, 4.90 VDD 5.10, Acceleration = 0g, Loaded output.(1)
)
Characteristic
Symbol
Min
Typ
Max
Unit
Operating Range(2)
Supply Voltage(3)
Supply Current
VDD
IDD
TA
4.90
1.1
–40
—
5.00
2.1
—
5.10
3.0
V
mA
°C
g
Operating Temperature Range
Acceleration Range
+105
—
gFS
5
Output Signal
+1g(4)
VOFF
S
0.41 VDD
380
0.5 VDD
400
0.58 VDD
420
V
Sensitivity (TA = 25°C, VDD = 5.0 V)(5)
Sensitivity
mV/g
mV/g/V
Hz
S
74.4
80.0
50
85.6
Bandwidth Response
Nonlinearity
f-3dB
NLOUT
42.5
57.5
–1.0
—
+1.0
% FSO
Noise
RMS (0.1 Hz – 1.0 kHz)
Spectral Density (RMS, 0.1 Hz – 1.0 KHz)(6)
nRMS
nSD
—
—
2.0
2.8
—
mVrms
Hz
600
g/
Self-Test
Output Response
Input Low
VST
VIL
VIH
IIN
0.2
VSS
0.7VDD
–300
—
0.25
—
0.3
0.3 VDD
VDD
V/V
V
Input High
—
V
Input Loading(7)
Response Time(8)
–125
2.0
–50
A
ms
tST
25
Status(9), (10)
Output Low (Iload = 100 A)
Output High (Iload = 100 A)
VOL
VOH
—
—
—
0.4
—
V
V
VDD – 0.8
Output Stage Performance
Electrical Saturation Recovery Time(11)
Full Scale Output Range (IOUT = 200 A)
Capacitive Load Drive(12)
tDELAY
VFSO
CL
—
VSS + 0.25
—
—
—
—
50
2.0
VDD – 0.25
100
ms
V
pF
Output Impedance
ZO
—
—
Mechanical Characteristics
Transverse Sensitivity(13)
VXZ,YZ
—
—
5.0
% FSO
1. For a loaded output the measurements are observed after an RC filter consisting of a 1 k resistor and a 0.1 F capacitor to ground.
2. These limits define the range of operation for which the part will meet specification.
3. Within the supply range of 4.9 and 5.1 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 +1g 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 3g. Sensitivity limits apply to 0Hz acceleration.
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 s, 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.
MMA1252
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Freescale Semiconductor, Inc.
3
PRINCIPLE OF OPERATION
The Freescale accelerometer is a surface-micromachined
SPECIAL FEATURES
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 (polysilicon) 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 = A/D). Where A is the area of the
plate, 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.
Filtering
The Freescale accelerometers contain an onboard 2-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 cutoff 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
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
2
2
1
2
V
force F = --A------ causes the center plate to deflect.
e
d
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.
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 the
following event occurs:
Acceleration
•
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 3. Transducer
Physical Model
Figure 4. Equivalent
Circuit Model
MMA1252
Sensors
Freescale Semiconductor, Inc.
4
BASIC CONNECTIONS
PCB Layout
Pinout Description
STATUS
ST
P1
16
15
14
13
12
11
10
9
VSS
VSS
VSS
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
1
2
3
4
5
6
7
8
P0
VSS
VOUT
VSS
A/D In
R
VOUT
STATUS
VDD
C
0.1 F
1 k
0.1 F
0.1 F
C
VDD
0.1 F
C
VSS
ST
VDD
VRH
C
Table 3. Pin Descriptions
Power Supply
Pin No.
Pin Name
Description
1 thru 3
VSS
Redundant connections to the internal
VSS and may be left unconnected.
Figure 6. Recommended PCB Layout for Interfacing
Accelerometer to Microcontroller
4
VOUT
Output voltage of the accelerometer.
NOTES:
5
STATUS Logic output pin to indicate fault.
1. Use a 0.1 F capacitor on VDD to decouple the power
source.
6
VDD
VSS
ST
The power supply input.
2. Physical coupling distance of the accelerometer to the
microcontroller should be minimal.
7
8
The power supply ground.
Logic input pin used to initiate self-test.
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.
9 thru 13
Trim pins Used for factory trim. Leave
unconnected.
4. Use an RC filter of 1 k and 0.1 F on the output of the
accelerometer to minimize clock noise (from the
switched capacitor filter circuit).
14 thru 16
—
No internal connection. Leave
unconnected.
5. PCB layout of power and ground should not couple
power supply noise.
6. Accelerometer and microcontroller should not be a
high current path.
5
MMA1252
STATUS
VDD
8
6
ST
LOGIC
INPUT
R1
1 k
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.
4
VDD
VOUT
OUTPUT
SIGNAL
VSS
VSS
VSS
1
2
3
C1
0.1 F
C2
0.1 F
7 VSS
Figure 5. SOIC Accelerometer with Recommended
Connection Diagram
MMA1252
Sensors
Freescale Semiconductor, Inc.
5
ACCELERATION SENSING DIRECTIONS
DYNAMIC ACCELERATION
16
15
14
13
12
11
VSS
VSS
N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C
1
2
3
4
5
6
7
8
VSS
+g
VOUT
STATUS
VDD
VSS
10
9
ST
16-Pin SOIC Package
N/C pins are recommended to be left FLOATING
–g
STATIC ACCELERATION
Direction of Earth's gravity field(1)
+1g
V
OUT = 2.5 V
0g
0g
VOUT = 2.1 V
VOUT = 2.1 V
-1g
VOUT = 1.7 V
1. When positioned as shown, the Earth's gravity will result in a positive 1g output
MMA1252
Sensors
Freescale Semiconductor, Inc.
6
PACKAGE DIMENSIONS
PAGE 1 OF 2
CASE 475-01
ISSUE C
16 LEAD SOIC
MMA1252
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Freescale Semiconductor, Inc.
7
PACKAGE DIMENSIONS
PAGE 2 OF 2
CASE 475-01
ISSUE C
16 LEAD SOIC
MMA1252
Sensors
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Freescale Semiconductor, Inc.
Revision History
Revision Revision
Description of changes
number
date
0
1
11/2009
07/2012
• Initial Release
• Removed KEG suffix from Device Number
• In Table 2. Operating Characteristics; updated min and typ values under Operating Range,
Supply Voltage, updated min and typ values under Output Signal, +1g, and updated min and typ
values under Output Signal, Sensitivity, and updated Noise, RMS max, Spectural Density, typ,
and updated footnotes 3 and 4, on page 6 updated Static Acceleration values
MMA1252
Sensors
9
Freescale Semiconductor, Inc.
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MMA1252
Rev. 1
07/2012
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