Motorola Sensor Device Data

Surface Mount

Micromachined Accelerometer

The MMA series of silicon capacitive, micromachined accelerometers

features signal conditioning, a 4pole low pass filter and temperature
compensation. Zerog offset full scale span and filter cutoff are factory set and
require no external devices. A full system selftest capability verifies system
functionality.

Features

Integral Signal Conditioning

Linear Output

Ratiometric Performance

4th Order Bessel Filter Preserves Pulse Shape Integrity

Calibrated Selftest

Low Voltage Detect, Clock Monitor, and EPROM Parity Check Status

Transducer Hermetically Sealed at Wafer Level for Superior Reliability

Robust Design, High Shocks Survivability

Typical Applications

Vibration Monitoring and Recording

Impact Monitoring

Appliance Control

Mechanical Bearing Monitoring

Computer Hard Drive Protection

Computer Mouse and Joysticks

Virtual Reality Input Devices

Sports Diagnostic Devices and Systems

SIMPLIFIED ACCELEROMETER FUNCTIONAL BLOCK DIAGRAM

G-CELL

SENSOR

INTEGRATOR

GAIN

FILTER

TEMP

COMP

SELF-TEST

CONTROL LOGIC &

EPROM TRIM CIRCUITS

CLOCK GEN.

OSCILLATOR

OUT

Figure 1. Simplified Accelerometer Functional Block Diagram

STATUS

REV 0

Order this document

by MMA2202D/D

MOTOROLA

SEMICONDUCTOR TECHNICAL DATA

MMA2202D

MMA2202D: X AXIS SENSITIVITY

MICROMACHINED

ACCELEROMETER

50g

16 LEAD SOIC

CASE 47501

N/C

N/C
N/C

OUT

STATUS

N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C

Pin Assignment

Motorola, Inc. 2001

MMA2202D

Motorola Sensor Device Data

MAXIMUM RATINGS

(Maximum ratings are the limits to which the device can be exposed without causing permanent damage.)

Rating

Symbol

Value

Unit

Powered Acceleration (all axes)

500

Unpowered Acceleration (all axes)

upd

2000

Supply Voltage

0.3 to +7.0

Drop Test

(1)

drop

1.2

Storage Temperature Range

stg

40 to +105

NOTES:

1. Dropped onto concrete surface from any axis.

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.

MMA2202D

Motorola Sensor Device Data

OPERATING CHARACTERISTICS

(Unless otherwise noted: 40

+85

C, 4.75

5.25, Acceleration = 0g, Loaded output

(1)

)

Characteristic

Symbol

Min

Typ

Max

Unit

Operating Range

(2)

Supply Voltage

(3)

Supply Current
Operating Temperature Range
Acceleration Range

4.75

4.0

5.00

5.0

5.25

6.0

+85

Output Signal

Zero g (V

= 5.0 V)

(4)

Zero g
Sensitivity (T

= 25

C, V

= 5.0 V)

(5)

Sensitivity
Bandwidth Response
Nonlinearity

OFF

OFF,V

3dB

OUT

2.3

0.44 V

7.4

360

1.0

2.5

0.50 V

400

2.7

0.56 V

8.6

440

+1.0

V
V

mV/g

mV/g/V

% FSO

Noise

RMS (.011 kHz)
Power Spectral Density
Clock Noise (without RC load on output)

(6)

RMS

PSD

CLK

--
--
--

110

2.0

2.8

--
--

mVrms

V/(Hz

1/2

)

mVpk

SelfTest

Output Response
Input Low
Input High
Input Loading

(7)

Response Time

(8)

0.7 x V

--
--

110

2.0

0.3 x V

300

V
V

Status

(12)(13)

Output Low (I

load

= 100

Output High (I

load

= 100

--
--

0.4

V
V

Minimum Supply Voltage (LVD Trip)

LVD

2.7

3.25

4.0

Clock Monitor Fail Detection Frequency

min

150

400

kHz

Output Stage Performance

Electrical Saturation Recovery Time

(9)

Full Scale Output Range (I

OUT

= 200

Capacitive Load Drive

(10)

Output Impedance

DELAY

FSO

0.3

--
--

0.2

--
--

300

0.3

100

Mechanical Characteristics

Transverse Sensitivity

(11)

Package Resonance

ZX,YX

PKG

--
--

5.0

% FSO

kHz

NOTES:

1. For a loaded output the measurements are observed after an RC filter consisting of a 1 k

resistor and a 0.01

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 4.75 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

/2 and for negative acceleration the output will decrease below V

/2.

5. The device is calibrated at 20g.
6. At clock frequency

70 kHz.

7. The digital input pin has an internal pulldown 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 selftest 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 powerup until at least one rising edge has been applied to the selftest pin. The Status pin is

high whenever the selftest 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 selftest, unless a fault condition continues to exist.

MMA2202D

Motorola Sensor Device Data

PRINCIPLE OF OPERATION

The Motorola accelerometer is a surfacemicromachined

integratedcircuit accelerometer.

The device consists of a surface micromachined capaci-

tive sensing cell (gcell) 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 gcell 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 inbetween. 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 gcell plates form two backtoback capacitors

(Figure 3). 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 gcell 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

Figure 2. Transducer

Physical Model

Figure 3. Equivalent

Circuit Model

SPECIAL FEATURES

Filtering

The Motorola accelerometers contain an onboard 4pole

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 cutoff frequency.

SelfTest

The sensor provides a selftest 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 gcell as a self
test plate. When the user applies a logic high input to the
selftest pin, a calibrated potential is applied across the
selftest plate and the moveable plate. The resulting elec-
trostatic force (Fe =

) 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
(gcell) 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 selftest, 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

N/C

N/C
N/C

OUT

STATUS

N/C
N/C
N/C
N/C
N/C
N/C
N/C
N/C

Pinout Description

MMA2202D

Motorola Sensor Device Data

Pin No.

Pin Name

Description

1 thru 3

No internal connection. Leave

unconnected.

Logic input pin used to initiate

selftest.

OUT

Output voltage of the accelerome-

ter.

STATUS

Logic output pin to indicate fault.

The power supply ground.

The power supply input.

9 thru 13

Trim pins

Used for factory trim. Leave

unconnected.

14 thru 16

No internal connection. Leave

unconnected.

MMA2202D

OUT

OUTPUT

SIGNAL

1 k

0.01

LOGIC

INPUT

0.1

Figure 4. SOIC Accelerometer with Recommended

Connection Diagram

STATUS

PCB Layout

A/D IN

OUT

0.01

1 k

0.1

C 0.1

POWER SUPPLY

0.1

MICROCONTROLLER

ACCELEROMETER

Figure 5. Recommend PCB Layout for Interfacing

Accelerometer to Microcontroller

STATUS

NOTES:

Use a 0.1

F capacitor on V

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 5.

Use an RC filter of 1 k

and 0.01

F 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.

Part Number MMA2202D