Freescale MMA6271QT User Manual

Freescale Semiconductor

Technical Data

±2.5g - 10g Two Axis Low-g Micromachined Accelerometer

The MMA6271QT low cost capacitive micromachined accelerometer features
signal conditioning, a 1-pole low pass filter, temperature compensation and g­Select which allows for the selection among 4 sensitivities. Zero-g offset full scale
span and filter cut-off are factory set and require no external devices. Includes a
Sleep Mode that makes it ideal for handheld battery powered electronics.

Document Number: MMA6271QT

Rev 2, 06/2007

MMA6271QT

Features

• Selectable Sensitivity (2.5g/3.3g/6.7g/10g)

• Low Current Consumption: 500 μA

• Sleep Mode: 3 μA

• Low Voltage Operation: 2.2 V – 3.6 V

• 6mm x 6mm x 1.45mm QFN

• Fast Turn On Time

• High Sensitivity (2.5 g)

• Integral Signal Conditioning with Low Pass Filter

• Robust Design, High Shocks Survivability

• Environmentally Preferred Package

• Low Cost

Typical Applications

• Laptop PC: Freefall Detection, Anti-Theft

• Cell Phone: Image Stability, Text Scroll, Motion Dialing, E-Compass

• Motion Sensing

• PDA: Text Scroll

• Navigation and Dead Reckoning: E-Compass Tilt Compensation

• Gaming: Tilt and Motion Sensing, Event Recorder

• Vibration: Shock Sensing

ORDERING INFORMATION

Device Temp. Range Case No. Package

MMA6271QT

MMA6271QR2

– 40 to +105°C 1622-02 QFN-16, Tray
– 40 to +105°C 1622-02 QFN-16,Tape & Reel

MMA6271QT: XY AXIS

ACCELEROMETER
±2.5g/3.3g/6.7g/10g

Bottom View

16-LEAD

QFN

CASE 1622-02

Top View

N/CN/C

1516 14 13

g-Select1

1

2

3

V

DD

V

4

SS

OUTYOUT

X

N/C

Sleep

12

Mode

11

N/Cg-Select2

10

N/C

9

N/C

© Freescale Semiconductor, Inc., 2005-2007. All rights reserved.

5678

N/C

N/C

N/C

Figure 1. Pin Connections

g-Select1
g-Select2

V

DD

Sleep Mode

G-Cell

Sensor

Oscillator

C to V

Converter

Control Logic

EEPROM Trim Circuits

Clock

Generator

Gain

+

Filter

V

SS

X-Temp

Comp

Y-Temp

Comp

Figure 2. Simplified Accelerometer Functional Block Diagram

T able 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

±2000 g

–0.3 to +3.6 V

1.8 m

–40 to +125 °C

X

OUT

Y

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

MMA6271QT

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: –20°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

(2)

(3)

(4)

V

DD

I

DD

I

DD

T

A

2.2
—
—

–40

3.3

500

3

—

3.6

800

10

+105

V

μA
μA

°C

Acceleration Range, X-Axis, Y-Axis

g-Select1 & 2: 00
g-Select1 & 2: 10
g-Select1 & 2: 01
g-Select1 & 2: 11

g

FS

g

FS

g

FS

g

FS

—
—
—
—

±2.5
±3.3
±6.7

±10.0

—
—
—
—

g
g
g
g

Output Signal

Zero-g (T
Zero-g

= 25°C, VDD = 3.3 V)

A

(4)

X-axis
Y-axis

Sensitivity (T

= 25°C, VDD = 3.3 V)

A

2.5g

3.3g

6.7g
10g

Sensitivity

(4)

X-axis
Y-axis

Bandwidth Response, XY

(5)

V

OFF

V

, T

OFF

A

V

, T

OFF

A

S

2.5g

S

3.3g

S

6.7g

S

10g

S,T

A

S,T

A

f

-3dB

1.485

±2.6
±5.8

444
333
167
111

±0.02
±0.01

—

1.65

(6)
(6)

±0.6
±5.8

480
360
180
120

(6)

±0.02

(6)

±0.01

350

1.815

±3.8
±5.9

516
387
193
129

±0.02
±0.01

—

(7)
(7)

(7)
(7)

V

mg/°C
mg/°C

mV/g
mV/g
mV/g
mV/g

%/°C
%/°C

Hz

Noise

RMS (0.1 Hz – 1 kHz)

(4)

Power Spectral Density RMS (0.1 Hz – 1 kHz)

(4)

n
n

RMS
PSD

—
—

3.0

350

—
—

mVrms

μg/

Hz

Control Timing

Power-Up Response Time
Enable Response Time

(8)

(9)

Sensing Element Resonant Frequency, XY
Internal Sampling Frequency

t

RESPONSE

t

ENABLE

f

GCELL

f

CLK

—
—
—
—

1.0

0.5

6.0
11

2.0

2.0
—
—

ms

ms
kHz
kHz

Output Stage Performance

Full-Scale Output Range (I

Nonlinearity, X
Cross-Axis Sensitivity

OUT

, Y

OUT

(10)

= 30 µA) V

OUT

NL

FSO

V

OUT

XY

1.For a loaded output, the measurements are observed after an RC filter consisting of a 1.0 kΩ resistor and a 0.1 µF capacitor on V

VSS+0.25 — VDD–0.25 V

–1.0 — +1.0 %FSO

——5.0 %

-GND.

DD

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 2.5g 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. These values represent the 10th percentile, not the minimum.

7. These values represent the 90th percentile, not the maximum.

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

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

DD

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

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

MMA6271QT

Sensors
Freescale Semiconductor 3

PRINCIPLE OF OPERATION

The Freescale accelerometer is a s urface-micromachined

integrated-circuit accelerometer.

The device consists of two surface micromachined

capacitive sensing cells (g-cell) and a signal conditioning
ASIC contained in a single integrated circuit package. The
sensing elements are sealed hermetically at the wafer level
using a bulk micromachined cap wafer.

The g-cell is a mechanical structure formed from

semiconductor materials (postillion) 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

g-Select

The g-Select feature allows for the selection among 4
sensitivities present in the device. Depending on the logic
input placed on pins 1 and 2, the device internal gain will be
changed allowing it to function with a 2.5g, 3.3g, 6.7g, or 10g
sensitivity (Table 3). This feature is ideal when a product has
applications requiring different sensitivities for optimum
performance. The sensitivity can be changed at anytime
during the operation of the product. The g-Select1 and g­Select2 pins can be left unconnected for applications
requiring only a 2.5g sensitivity as the device has an internal
pull-down to keep it at that sensitivity (480 mV/g).

Table 3. g-Select Pin Descriptions

g-Select2 g-Select1 g-Range Sensitivity

0 0 2.5g 480 mV/g
0 1 3.3g 360 mV/g
1 0 6.7g 180 mV/g
1 1 10g 120 mV/g

Sleep Mode

The 2 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 12
(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-Select1 and g-Select2 to 2.5g mode.
By placing a high input signal on pin 12, the device will
resume to normal mode of operation.

Filtering

The 2 axis accelerometer contains onboard single-pole
switched capacitor filters. 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.

Figure 3. Simplified Transducer Physical Model

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.

MMA6271QT

Sensors

4 Freescale Semiconductor