Freescale MMA7368L User Manual

Freescale Semiconductor

Technical Data

±1.5g Three Axis Low-g

Document Number: MMA7368L

Rev 0, 05/2008

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 Mode: 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 Reckoning: E-Compass Tilt Compensation

• Robotics: Motion Sensing

ORDERING INFORMATION

Part Number

MMA7368LR2

Temperature

Range

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

Package
Drawing

Package Shipping

MMA7368L

MMA7368L: XYZ AXIS

ACCELEROMETER

±1.5g

Bottom View

14 LEAD

LGA

CASE 1977-01

Top View

N/C

14

7

X

Y

Z

N/C

OUT

OUT

OUT

V

SS

V

DD

123456

Self Test

N/C

N/C

N/C

N/C

8 9 10 11 12 13

N/C

© Freescale Semiconductor, Inc., 2008. All rights reserved.

Sleep

Figure 1. Pin Connections

OSCILLATOR

CLOCK

GEN

X-TEMP

COMP

X

OUT

Sleep Mode

Selftest

G-CELL

SENSOR

C to V

CONVERTER

SELFTEST

CONTROL LOGIC

V

SS

GAIN

+

FILTER

NVM TRIM
CIRCUITS

Y-TEMP

COMP

Z-TEMP

COMP

Figure 2. 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 Value Unit

Maximum Acceleration (all axis) g
Supply Voltage V
Drop Test
Storage Temperature Range T

1. Dropped onto concrete surface from any axis.

(1)

max

DD

D

drop

stg

±5000 g

–0.3 to +3.6 V

1.8 m

–40 to +125 °C

Y

OUT

Z

OUT

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

MMA7368L

2 Freescale Semiconductor

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.

Sensors

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

Supply Voltage
Supply Current
Supply Current at Sleep Mode
Operating Temperature Range
Acceleration Range, X-Axis, Y-Axis, Z-Axis

(2)

(3)

(4)

(4)

V

DD

I

DD

I

DD

T

A

g

FS

2.2
—
—

-40
—

3.3

400

3

—

±1.5

3.6

600

10

+85

—

V

μA
μA

°C

g

Output Signal

Zero-g (T

(4)

Zero-g

= 25°C, VDD = 3.3 V)

A

(5), (6)

V

OFF

V

, T

OFF

A

1.485

-2.0

1.65
±0.5

1.815
+2.0

V

mg/°C

Sensitivity (TA = 25°C, VDD = 3.3 V)

1.5g

Sensitivity

S

(4)

S,T

1.5g
A

740

-0.0075

800

±0.002

860

+0.0075

mV/g
%/°C

Bandwidth Response

XY
Z

f

-3dBXY

f

-3dBZ

—
—

400
300

—
—

Hz
Hz

Self Test

Output Response

X

, Y

OUT

Z

OUT

Input Low
Input High

OUT

Δg

Δg

STXY

STZ

V

IL

V

IH

-0.05
+0.8

V

0.7 V

SS

DD

-0.1

+1.0

—
—

—

+1.2

0.3 V
V

DD

DD

g
g
V
V

Noise

Power Spectral Density RMS (0.1 Hz – 1 kHz)

(4)

n

PSD

— 350 — μg/

Hz

Control Timing

Power-Up Response Time
Enable Response Time

(8)

Self Test Response Time

(7)

(9)

t

RESPONSE

t

ENABLE

t

ST

—
—
—

1.0

0.5

2.0

2.0

2.0

5.0

ms
ms
ms

Sensing Element Resonant Frequency

XY
Z

Internal Sampling Frequency

f

GCELLXY

f

GCELLZ

f

CLK

—
—
—

6.0

3.4
11

—
—
—

kHz
kHz
kHz

Output Stage Performance

Full-Scale Output Range (I

Nonlinearity, X
Cross-Axis Sensitivity

OUT

, Y

OUT

(10)

= 3 µA) V

OUT

, Z

OUT

FSO

NL

OUT

V

XY, XZ, YZ

VSS+0.1 — VDD–0.1 V

-1.0 — +1.0 %FSO

-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 V

2. These limits define the range of operation for which the part will meet specification.

- GND.

DD

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 V

/2. For negative acceleration, the output will decrease below VDD/2.

DD

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

7. The response time between 10% of full scale V

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

input voltage and 90% of the final operating output voltage.

DD

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.

MMA7368L

Sensors
Freescale Semiconductor 3

PRINCIPLE OF OPERATION

The Freescale 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.

Acceleration

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.
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 slightly
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.

This

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

Figure 3. Simplified Transducer Physical Model

MMA7368L

4 Freescale Semiconductor

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.

Sensors