MMA1212D - Freescale Semiconductor

MMA1212D

Rev 4, 03/2006

Freescale Semiconductor

Technical Data

Surface Mount

Micromachined Accelerometer

The MMA series of silicon capacitive, micromachined accelerometers feature

signal conditioning, a 4-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

• Ratiometric Performance

•4

th Order Bessel Filter Preserves Pulse Shape Integrity

• Calibrated Self-test

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

• Transducer Hermetically Sealed at Wafer Level for Superior Reliability

• Robust Design, High Shocks Survivability

Functional Description

• Vibration Monitoring and Recording

• Impact Monitoring

ORDERING INFORMATION

Device Name Temperature Range Case No. Package

MMA1212D –40° to 125°C475-01 SOIC-16

MMA1212DR2 –40° to 125°C475-01 SOIC16, Tape & Reel

MMA1212EG –40° to 125°C475-01 SOIC-16

MMA1212EGR2 –40° to 125°C475-01 SOIC16, Tape & Reel

MMA1212

MMA1212D: Z AXIS SENSITIVITY

MICROMACHINED

ACCELEROMETER

±200g

D SUFFIX

EG SUFFIX (Pb-FREE)

16-LEAD SOIC

CASE 475-01

G-Cell

Sensor Integrator Gain Filter Temp

Comp

Self-test Control Logic &

EPROM Trim Circuits Clock

Generator

Oscillator

VDD

VOUT

VSS

STATUS

Figure 1. Simplified Accelerometer Functional Block Diagram

N/C

VOUT

STATUS

VSS

VDD

N/C

Figure 2. Pin Connections

MMA1212D

Sensors

2Freescale Semiconductor

ELECTRO STATIC DISCHARGE (ESD)

WARNING: This device is sensitive to electrostatic

discharge.

Although the Freescale 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

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.

Table 1. 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) Gpd 1500 g

Unpowered Acceleration (all axes) Gupd 2000 g

Supply Voltage VDD –0.3 to +7.0 V

Drop Test (1)

1. Dropped onto concrete surface from any axis.

Ddrop 1.2 m

Storage Temperature Range Tstg –40 to +125 °C

MMA1212D

Sensors

Freescale Semiconductor 3

Table 2. Operating Characteristics

(Unless otherwise noted: –40°C ≤ TA ≤ +105°C, 4.75 ≤ VDD ≤ 5.25, Acceleration = 0g, Loaded output.(1))

1. For a loaded output the measurements are observed after an RC filter consisting of a 1 kΩ resistor and a 0.01 µF capacitor to ground.

Characteristic Symbol Min Typ Max Unit

Operating Range (2)

Supply Voltage(3)

Supply Current

Operating Temperature Range

Acceleration Range

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 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.

VDD

IDD

gFS

4.75

3.0

–40

—

5.00

—

225

5.25

6.0

+125

—

Output Signal

Zero g (TA = 25°C, VDD = 5.0 V)(4)

Zero g

Sensitivity (TA = 25°C, VDD = 5.0 V)(5)

Sensitivity

Bandwidth Response

Nonlinearity

4. The device can measure both + and – acceleration. With no input acceleration the output is at mid supply. 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 35g.

VOFF

VOFF,V

f–3dB

NLOUT

2.35

0.47VDD

9.5

1.86

360

–2.0

2.5

0.50 VDD

400

—

2.65

0.53 VDD

10.5

2.14

440

2.0

mV/g

mV/g/V

% FSO

Noise

RMS (0.1-1 kHz)

Power Spectral Density

Clock Noise (without RC load on output)(6)

6. At clock frequency ≅70 kHz.

nRMS

nPSD

nCLK

—

110

2.0

2.8

—

mVrms

µV/(Hz1/2)

mVpk

Self-Test

Output Response

Input Low

Input High

Input Loading(7)

Response Time(8)

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.

gST

VIL

VIH

IIN

tST

VSS

0.7 × VDD

–30

—

–100

2.0

0.3 × VDD

VDD

–260

µA

Status(9), (10)

Output Low (Iload = 100 µA)

Output High (Iload = 100 µA)

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 µs, unless a fault condition continues to exist.

VOL

VOH

—

VDD –.8

—

0.4

—

Minimum Supply Voltage (LVD Trip) VLVD 2.7 3.25 4.0 V

Clock Monitor Fail Detection Frequency fMIN 50 —260 kHz

Output Stage Performance

Electrical Saturation Recovery Time(11)

Full Scale Output Range (IOUT = 200 µA)

Capacitive Load Drive(12)

Output Impedance

11. Time for amplifiers to recover after an acceleration signal causes them to saturate.

12. Preserves phase margin (60°) to guarantee output amplifier stability.

tDELAY

VFSO

—

0.25

—

0.2

—

300

—

VDD–0.25

100

—

Mechanical Characteristics

Transverse Sensitivity(13)

Package Resonance

13. A measure of the device's ability to reject an acceleration applied 90° from the true axis of sensitivity.

VXZ,YZ

fPKG

—

5.0

—

% FSO

kHz

MMA1212D

Sensors

4Freescale Semiconductor

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 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 (poly silicon) 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 = Aε/D). Where A is the area of the

plate, ε 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.

SPECIAL FEATURES

Filtering

The Freescale accelerometers contain an on board 4-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 cut-off 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 air bag

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

force (Fe = 1/2AV2/d2) causes the center plate to deflect. 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.

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

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 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 falling edge on the self-

test input pin, unless one (or more) of the fault conditions

continues to exist.

Acceleration

Figure 3. Transducer

Physical Model

Figure 4. Equivalent

Circuit Model

MMA1212D

Sensors

Freescale Semiconductor 5

BASIC CONNECTIONS

Pinout Description

Figure 5. SOIC Accelerometer with Recommended

Connection Diagram

PCB Layout

Figure 6. Recommended PCB Layout for Interfacing

Accelerometer to Microcontroller

NOTES:

1. Use a 0.1 µF capacitor on VDD to decouple the power

source.

2. Physical coupling distance of the accelerometer to the

microcontroller should be minimal.

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.

4. Use an RC filter of 1 kΩ and 0.01 µF on the output of

the accelerometer to minimize clock noise (from the

switched capacitor filter circuit).

5. PCB layout of power and ground should not couple

power supply noise.

6. Accelerometer and microcontroller should not be a

high current path.

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.

Table 3. Pin Descriptions

Pin No. Pin Name Description

1 thru 3 —Leave unconnected

4ST Logic input pin used to initiate self-test

5 VOUT Output voltage of the accelerometer

6STATUS Logic output pin to indicate fault

7 VSS The power supply ground

8 VDD The power supply input

9 thru 13 Trim pins Used for factory trim. Leave

unconnected

14 thru 16 —No internal connection. Leave

unconnected

N/C

VOUT

STATUS

VSS

VDD

N/C

MMA1212D

VOUT Output

Signal

1 kΩ

0.01 µF

Logic

Input

VDD

0.1 µF

6STATUS

8VDD

VSS

A/D In

VRH

VSS

VDD

VOUT

VSS

VDD

0.01 µF1 kΩ

0.1 µF

Power Supply

0.1 µF

P1STATUS

Microcontroller

Accelerometer

MMA1212D

Sensors

6Freescale Semiconductor

Acceleration of the package in the

+Z direction (center plate moves in

the −Z direction) will result in an

increase in the output.

−Z

Side View

Activation of Self test moves the

center plate in the −Z direction,

resulting in an increase in the output.

1. When positioned as shown, the Earth's gravity will result in a positive 1g output.

Direction of Earth's gravity field(1)

Side View

Dynamic Acceleration Sensing Direction

Static Acceleration Sensing Direction

Sensors

Freescale Semiconductor 7

MMA1212D

MINIMUM RECOMMENDED FOOTPRINT FOR SURFACE MOUNTED APPLICATIONS

Surface mount board layout is a critical portion of the total

design. The footprint for the surface mount packages must be

the correct size to ensure proper solder connection interface

between the board and the package. With the correct

footprint, the packages will self-align when subjected to a

solder reflow process. It is always recommended to design

boards with a solder mask layer to avoid bridging and

shorting between solder pads.

Figure 7. Footprint SOIC-16 (Case 475-01)

0.380 in.

9.65 mm

0.050 in.

1.27 mm

0.024 in.

0.610 mm

0.080 in.

2.03 mm

MMA1212D

Sensors

8Freescale Semiconductor

PACKAGE DIMENSIONS

CASE 475-01

ISSUE C

16-LEAD SOIC

PAGE 1 OF 2

MMA1212D

Sensors

Freescale Semiconductor 9

PACKAGE DIMENSIONS

CASE 475-01

ISSUE C

16-LEAD SOIC

PAGE 2 OF 2

How to Reach Us:

Home Page:

www.freescale.com

E-mail:

support@freescale.com

USA/Europe or Locations Not Listed:

Freescale Semiconductor

Technical Information Center, CH370

1300 N. Alma School Road

Chandler, Arizona 85224

+1-800-521-6274 or +1-480-768-2130

support@freescale.com

Europe, Middle East, and Africa:

Freescale Halbleiter Deutschland GmbH

Technical Information Center

Schatzbogen 7

81829 Muenchen, Germany

+44 1296 380 456 (English)

+46 8 52200080 (English)

+49 89 92103 559 (German)

+33 1 69 35 48 48 (French)

support@freescale.com

Japan:

Freescale Semiconductor Japan Ltd.

Headquarters

ARCO Tower 15F

1-8-1, Shimo-Meguro, Meguro-ku,

Tokyo 153-0064

Japan

0120 191014 or +81 3 5437 9125

support.japan@freescale.com

Asia/Pacific:

Freescale Semiconductor Hong Kong Ltd.

Technical Information Center

2 Dai King Street

Tai Po Industrial Estate

Tai Po, N.T., Hong Kong

+800 2666 8080

support.asia@freescale.com

For Literature Requests Only:

Freescale Semiconductor Literature Distribution Center

P.O. Box 5405

Denver, Colorado 80217

1-800-441-2447 or 303-675-2140

Fax: 303-675-2150

LDCForFreescaleSemiconductor@hibbertgroup.com

MMA1212D

Rev. 4

03/2006

RoHS-compliant and/or Pb-free versions of Freescale products have the functionality

and electrical characteristics of their non-RoHS-compliant and/or non-Pb-free

counterparts. For further information, see http://www.freescale.com or contact your

Freescale sales representative.

For information on Freescale’s Environmental Products program, go to http://

www.freescale.com/epp.

Information in this document is provided solely to enable system and software

implementers to use Freescale Semiconductor products. There are no express or

implied copyright licenses granted hereunder to design or fabricate any integrated

circuits or integrated circuits based on the information in this document.

Freescale Semiconductor reserves the right to make changes without further notice to

any products herein. Freescale Semiconductor makes no warranty, representation or

guarantee regarding the suitability of its products for any particular purpose, nor does

Freescale Semiconductor assume any liability arising out of the application or use of any

product or circuit, and specifically disclaims any and all liability, including without

limitation consequential or incidental damages. “Typical” parameters that may be

provided in Freescale Semiconductor data sheets and/or specifications can and do vary

in different applications and actual performance may vary over time. All operating

parameters, including “Typicals”, must be validated for each customer application by

customer’s technical experts. Freescale Semiconductor does not convey any license

under its patent rights nor the rights of others. Freescale Semiconductor products are

not designed, intended, or authorized for use as components in systems intended for

surgical implant into the body, or other applications intended to support or sustain life,

or for any other application in which the failure of the Freescale Semiconductor product

could create a situation where personal injury or death may occur. Should Buyer

purchase or use Freescale Semiconductor products for any such unintended or

unauthorized application, Buyer shall indemnify and hold Freescale Semiconductor and

its officers, employees, subsidiaries, affiliates, and distributors harmless against all

claims, costs, damages, and expenses, and reasonable attorney fees arising out of,

directly or indirectly, any claim of personal injury or death associated with such

unintended or unauthorized use, even if such claim alleges that Freescale

Semiconductor was negligent regarding the design or manufacture of the part.

Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc.

All other product or service names are the property of their respective owners.