Freescale MMA7331L User Manual

Freescale Semiconductor

Technical Data

±4g, ±12g Three Axis Low-g

Document Number: MMA7331L

Rev 0, 04/2008

Micromachined Accelerometer

The MMA7331L is a low power, low profile capacitive micromachined accelerometer featuring signal conditioning, a 1-pole low pass filter, temperature compensation, self test, and g-Select which allows for the selection between 2 sensitivities. Zero-g offset and sensitivity are factory set and require no external devices. The MMA7331L 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

• Selectable Sensitivity (±4g, ±12g)

• 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

MMA7331LT

MMA7331LR1 MMA7331LR2

Temperature

Range

-40 to +85°C 1977-01 LGA-14 Tray

-40 to +85°C 1977-01 LGA-14 7” Tape & Reel

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

Package Drawing

Package Shipping

MMA7331L

MMA7331L: XYZ AXIS

ACCELEROMETER

±4g, ±12g

Bottom View

14 LEAD

LGA

CASE 1977-01

Top View

N/C

123456

OUT

Sleep

Self Test

N/C

g-Select

N/C

8 9 10 11 12 13

N/C

* This document contains certain information on a new product. Specifications and information herein are subject to change without notice.

Figure 1. Pin Connections

g-Select

Sleep

Self Test

G-CELL

SENSOR

OSCILLATOR

C to V

CONVERTER

SELFTEST

CLOCK

GEN

GAIN

FILTER

CONTROL LOGIC

NVM TRIM

CIRCUITS

X-TEMP

COMP

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.)

OUT

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)

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.

max

drop

stg

±5000 g

–0.3 to +3.6 V

1.8 m

–40 to +125 °C

MMA7331L

Sensors

2 Freescale Semiconductor

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

(2)

(3)

(4)

2.2 — —

-40

2.8

400

—

3.6

600

+85

μA μA

°C

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

g-Select: 0 g-Select: 1

— —

±4

±12

— —

g g

Output Signal

Zero g (T

(4)

Zero g

= 25°C, VDD = 2.8 V)

(5), (6)

OFF

, T

OFF

1.316

-2.0

1.4

±0.5

1.484 +2.0

mg/°C

Sensitivity (TA = 25°C, VDD = 2.8 V)

4g 12g

Sensitivity

(4)

S,T

12g

289.5

75.2

-0.0075

308

83.6

±0.002

326.5

91.9

+0.0075

mV/g mV/g %/°C

Bandwidth Response

XY Z

Output Impedance

-3dBXY

-3dBZ

— — 24

400 300

— — 40

Hz Hz kΩ

Self Test

Output Response

, Y

OUT

Input Low Input High

OUT

Δg

STXY

STZ

+0.05

+0.8

0.7 V

-0.1

+1.0

— —

—

+1.2

0.3 V V

g g V V

Noise

Power Spectral Density RMS (0.1 Hz – 1 kHz)

(4)

PSD

— 350 — μg/

Control Timing

Power-Up Response Time Enable Response Time Self Test Response Time

(7)

(8)

(9)

RESPONSE

ENABLE

— — —

1.0

0.5

2.0

5.0

ms ms ms

Sensing Element Resonant Frequency

XY Z

Internal Sampling Frequency

GCELLXY

GCELLZ

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

OUT

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 32kΩ resistor and an external 3.3nF capacitor (recommended as a minimum to filter clock noise) on the analog output for each axis and a 0.1μF capacitor on V bandwidth is determined by the Capacitor added on the output. f = 1/2π * (32 x 10

) * C. C = 3.3 nF corresponds to BW = 1507HZ, which is

- GND. The output sensor

the minimum to filter out internal clock noise.

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 4g 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.

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

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

input voltage and 90% of the final operating 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.

MMA7331L

Sensors Freescale Semiconductor 3

PRINCIPLE OF OPERATION

The Freescale accelerometer is a s urface-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

g-Select

The g-Select feature allows for the selection between two sensitivities. Depending on the logic input placed on pin 10, the device internal gain will be changed allowing it to function with a 4g or 12g sensitivity (Table 3). This feature is ideal when a product has applications requiring two different sensitivities for optimum performance. The sensitivity can be changed at anytime during the operation of the product. The g-Select pin can be left unconnected for applications requiring only a 4g sensitivity as the device has an internal pull-down to keep it at that sensitivity (308mV/g)).

Table 3. g-Select Pin Description

g-Select g-Range Sensitivity

0 4g 308 mV/g 1 12g 83.6 mV/g

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 4g 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

Figure 3. Simplified Transducer Physical Model

SPECIAL FEA T URES

it provides system level cancellation of supply induced errors in the analog to digital conversion process.

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. 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.

MMA7331L

Sensors

4 Freescale Semiconductor

+ 7 hidden pages

Freescale MMA7331L User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

ELECTRO STATIC DISCHARGE (ESD)

PRINCIPLE OF OPERATION

Table 3. g-Select Pin Description

SPECIAL FEA T URES