MMA7368LR2 - Freescale Semiconductor / Motorola

Document Number: MMA7368L

Rev 0, 05/2008

Freescale Semiconductor

Technical Data

±1.5g Three Axis Low-g

Micromachined Accelerometer

The MMA7368L is a low power, low profile capacitive micromachined

accelerometer featuring signal conditioning, a 1-pole low pass filter,

temperature compensation, and self test. Zero-g offset and sensitivity are

factory set and require no external devices. The MMA7368L includes a Sleep

Mode that makes it ideal for handheld battery powered electronics.

Features

• 3mm x 5mm x 1.0mm LGA-14 Package

• Low Current Consumption: 400 μA

• Sleep Mod e : 3 μA

• Low Voltage Operation: 2.2 V – 3.6 V

• High Sensitivity (800 mV/g @ 1.5g)

• Fast Turn On Time (0.5 ms Enable Response Time)

• Self Test for Freefall Detect Diagnosis

• Signal Conditioning with Low Pass Filter

• Robust Design, High Shocks Survivability

• RoHS Compliant

• Environmentally Preferred Product

• Low Cost

Typical Applications

• 3D Gaming: Tilt and Motion Sensing, Event Recorder

• 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 Reckonin g: E-Compass Tilt Compensation

• Robotics: Motion Sensing

ORDERING INFORMATION

Part Number Temperature

Range Package

Drawing Package Shipping

MMA7368LR2 –40 to +85°C 1977-01 LGA-14 13” Tape & Reel

MMA7368L

MMA7368L: XYZ AXIS

ACCELEROMETER

±1.5g

14 LEAD

LGA

CASE 1977-01

Bottom View

Figure 1. Pin Connectio ns

Top View

123456

8 9 10 11 12 13

N/C

OUT

Sleep

N/C

Self Test

N/C

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MMA7368L

Figure 2. Simplified Accelerometer Functional Block Diagram

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.

Table 1. Maximum Ratings

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

Rating Symbol Value Unit

Maximum Acceleration (all axis) gmax ±5000 g

Supply Voltage VDD –0.3 to +3.6 V

Drop Test(1)

1. Dropped onto concrete surface from any axis.

Ddrop 1.8 m

Storage Temperature Range Tstg –40 to +125 °C

C to V

CONVERTER

XOUT

YOUT

ZOUT

OSCILLATOR CLOCK

GEN

Sleep Mode

X-TEMP

COMP

G-CELL

SENSOR GAIN

FILTER

CONTROL LOGIC

NVM TRIM

CIRCUITS

Y-TEMP

COMP

Z-TEMP

COMP

VSS

Selftest SELFTEST

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Table 2. Operating Characteristics

Unless otherwise noted: -40°C < TA < 85°C, 2.2 V < VDD < 3.6 V, Acceleration = 0g, Loaded output(1)

Characteristic Symbol Min Typ Max Unit

Operating Range(2)

Supply Voltage(3)

Supply Current(4)

Supply Current at Sleep Mode(4)

Operating Temperature Range

Acceleration Range, X-Axis, Y-Axis, Z-Axis

VDD

IDD

gFS

2.2

—

-40

—

3.3

400

—

±1.5

3.6

600

+85

—

μA

°C

Output Signal

Zero-g (TA = 25°C, VDD = 3.3 V)(5), (6)

Zero-g(4)

Sensitivity (TA = 25°C, VDD = 3.3 V)

1.5g

Sensitivity(4)

Bandwidth Response

VOFF

VOFF, TA

S1.5g

S,TA

f-3dBXY

f-3dBZ

1.485

-2.0

740

-0.0075

—

1.65

±0.5

800

±0.002

400

300

1.815

+2.0

860

+0.0075

—

mg/°C

mV/g

%/°C

Self Test

Output Response

XOUT, YOUT

ZOUT

Input Low

Input High

ΔgSTXY

ΔgSTZ

VIL

VIH

-0.05

+0.8

VSS

0.7 VDD

-0.1

+1.0

—

+1.2

0.3 VDD

VDD

Noise

Power Spectral Density RMS (0.1 Hz – 1 kHz)(4) nPSD — 350 — μg/

Control Timing

Power-Up Response Time(7)

Enable Response Time(8)

Self Test Response Time(9)

Sensing Element Resonant Frequency

Internal Sampling Frequency

tRESPONSE

tENABLE

tST

fGCELLXY

fGCELLZ

fCLK

—

1.0

0.5

2.0

6.0

3.4

2.0

5.0

—

kHz

Output Stage Performance

Full-Scale Output Range (IOUT = 3 µA) VFSO VSS+0.1 — VDD–0.1 V

Nonlinearity, XOUT, YOUT, ZOUT NLOUT -1.0 — +1.0 %FSO

Cross-Axis Sensitivity(10) VXY, XZ, YZ -5.0 — +5.0 %

1. For a loaded output, the measurements are observed after an RC filter consisting of an internal resistor and an external 0.1uF capacitor

(recommended as a minimum to filter clock noise) on the analog output for each axis and a 0.1μF capacitor on VDD - 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 1.5g 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 VDD/2. For negative acceleration, the output will decrease below VDD/2.

6. For optimal 0g offset performance, adhere to AN3484 and AN3447

7. The response time between 10% of full scale VDD input voltage and 90% of the final oper ating output voltage.

8. The response time between 10% of full scale Sleep Mode input voltage and 90% of the final operating output voltage.

9. The response time between 10% of the full scale self test input voltage and 90% of the self test output voltage.

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

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PRINCIPLE OF OPERAT ION

The Freescal e accelerometer is a surf ace-micromachined

integrated-circuit accelerometer.

The device consists of a surface micromachined

capacitive sensing cell (g-cell) and a signal conditioning ASIC

contained in a single 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 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.

Figure 3. Simplified Transducer Physical Model

SPECIAL FEATURES

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 hard disk drive

protection where system integrity must be ensured over the

life of the product. Customers can use self test to verify the

solderability to confirm that the part was mounted to the PCB

correctly. To use this feature to verify the 0g-Detect function,

the accelerometer should be held upside down so that the

z-axis experiences -1g. When the self test function is

initiated, an electrostatic force is applied to each axis to

cause it to deflect. The x- and y-axis are deflected slig htly

while the z-axis is trimmed to deflect 1g. This procedure

assures that both the mechanical (g-cell) and electronic

sections of the accelerometer are functioning.

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 7

(Sleep Mode) will place the device in this mode and reduce

the current to 3 μA typ. For lower power consumption, it is

recommended to set g-Select to 1.5g mode. By placing a high

input signal on pin 7, the device will resume to normal mode

of operation.

Filtering

The 3 axis accelerometer contains an onboard single-pole

switched capacitor filter. 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.

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.

Acceleration

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MMA7368L

BASIC CONNECTIONS

Pin Descriptions

Figure 4. Pinout Description

Figure 5. Acce lerometer with Recommended

Connection Diagram

PCB Layout

Figure 6. Recommende d PCB La y ou t for In terfa c ing

Accelerometer to Microcontroller

NOTES:

1. Use 0.1 µF capacitor on V DD 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 a 0.1uF capacitor on the outputs 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 shoul d 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.

Table 3 . Pin Descriptions

Pin No.

Pin Name Description

1 N/C No internal connection

Leave unconnected

OUT X direction output voltage

OUT Y direction output voltage

OUT Z direction output voltage

5 VSS Power Supply Ground

DD Power Supply Input

7 Sleep

Logic input pin to enable product or Sleep Mode

8 NC No internal connection

Leave unconnected

9 NC Leave unconnected

10 NC Leave unconnected

11 N/C Unused for factory trim

Leave unconnected

12 N/C Unused for factory trim

Leave unconnected

13 Self Test Input pin to initiate Self Test

14 N/C Unused for factory trim

Leave unconnected

123456

8 9 10 11 12 13

N/C

XOUT

ZOUT

YOUT

VSS

VDD

Sleep

N/C

Self Test

N/C

Top View

0.1 μF

Logic

Input

Logic

Input

0.1 μF

VDD

VSS

Self Test

Sleep

XOUT

YOUT

ZOUT

MMA7368L

POWER SUPPLY

VDD

VSS

Sleep

OUT

Accelerometer

VDD

VSS

VRH

A/DIN

CCC

Microcontroller

Self Test

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MMA7368L

Side View

XOUT @ 0g = 1.65 V

YOUT @ +1g = 2.45 V

ZOUT @ 0g = 1.65 V

XOUT @ +1g = 2.45 V

YOUT @ 0g = 1.65 V

ZOUT @ 0g = 1.65 V

XOUT @ -1g = 0.85 V

YOUT @ 0g = 1.65 V

ZOUT @0g=1.65V

XOUT @ 0g = 1.65 V

YOUT @ -1g = 0.85 V

ZOUT @ 0g = 1.65 V

Direction of Earth's gravity field.*

Top View

XOUT @ 0g = 1.65 V

YOUT @ 0g = 1.65 V

ZOUT @ -1g =0.85 V

XOUT @ 0g = 1.65 V

YOUT @ 0g = 1.65 V

ZOUT @ +1g = 2.45 V

Top

Bottom

123456

8 9 10 11 12 13

123456

8 9 10 11 12 13

13 12 11 10 9 8

12 34 56

14 7

123456

8 9 10 11 12 13

Top View

Side View

-Y

+X +Z-X -Z

Top

Bottom

: Arrow indicates direction of package movement.

14-Pin LGA Package

123456

8 9 10 11 12 13

DYNAMIC ACCELERATION

STATIC ACCELERATION

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

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MMA7368L

Figure 7. MMA7368L Temperature Coefficient of Offset (TCO) and

Temperature Coefficient of Sensitivity (TCS) Distributio n Ch arts

LSL USLTarget

-2 -1 0 1 2

X- T C O mg/degC

LSL USLTarget

-2 -1 0 1 2

Y- T C O mg/degC

LSL USLTarget

-2 -1 0 1 2

Z-TC O mg/ degC

LSL USLTarget

-0.01 -0.005 0.005 .01

X-TCS %/degC

LSL USLTarget

-0.01 -0.005 0.005 .01

Y-TCS %/degC

LSL USLTarget

-0.01 -0.005 0.005 .01

Z-TC S %/ degC

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MMA7368L

MINIMUM RECOMMENDED FOOTPRINT FOR SURFACE MOUNTED APPLICATIONS

PCB Mounting Recom mendations

MEMS based sensors are sensitive to Printed Circuit

Board (PCB) reflow processes. For optimal zero-g offset after

PCB mounting, care must be taken to PCB layout and reflow

conditions. Reference application note AN3484 for best

practices to minimize the zero-g offset shift after PCB

mounting.

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 shorti ng between solder pads. 6x2

12x1

14x0.9

14x0.6

10x0.8

113

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MMA7368L

PACKAGE DIMENSIONS

CASE 1977-01

ISSUE A

14-LEAD LGA

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MMA7368L

PACKAGE DIMENSIONS

CASE 1977-01

ISSUE A

14-LEAD LGA

MMA7368L

Rev. 0

05/2008

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