Freescale Semiconductor Technical Data
Document Number: MMA7260QT Rev 0, 10/2006
±1.5g - 6g Three Axis Low-g Micromachined Accelerometer
r />The MMA7260QT low cost capacitive micromachined accelerometer features signal conditioning, a 1-pole low pass filter, temperature compensation and g-Select 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. Features ? ? ? ? ? ? ? ? ? ? ? ? Selectable Sensitivity (1.5g/2g/4g/6g) Low Current Consumption: 500 ?A Sleep Mode: 3 ?A Low Voltage Operation: 2.2 V – 3.6 V 6mm x 6mm x 1.45mm QFN High Sensitivity (800 mV/g @ 1.5g) Fast Turn On Time Integral Signal Conditioning with Low Pass Filter Robust Design, High Shocks Survivability Pb-Free Terminations Environmentally Preferred Package Low Cost
MMA7260QT: XYZ AXIS ACCELEROMETER ±1.5g/2g/4g/6g
Typical Applications ? ? ? ? ? ? ? ? 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 Gaming: Tilt and Motion Sensing, Event Recorder Robotics: Motion Sensing
16 LEAD QFN CASE 1622-02
XOUT YOUT ZOUT
14 13 12 Sleep Mode
Device Name MMA7260QT MMA7260QR2 Temperature Range –20 to +85°C –20 to +85°C Package Drawing 1622-02 1622-02 Package QFN-16, Tray QFN-16,Tape & Reel
g-Select2 2 VDD 3 VSS 4 5 N/C 6 N/C 7 N/C 8 N/C
11 N/C 10 N/C 9 N/C
Figure 1. Pin Connections
? Freescale Semiconductor, Inc., 2006. All rights reserved.
g-Select1 g-Select2 Oscillator Clock Generator X-Temp Comp XOUT
C to V Converter
Gain + Filter
Control Logic EEPROM Trim Circuits
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 Maximum Acceleration (all axis) Supply Voltage Drop Test(1) Storage Temperature Range 1. Dropped onto concrete surface from any axis. Symbol gmax VDD Ddrop Tstg Value ±2000 –0.3 to +3.6 1.8 –40 to +125 Unit g V m °C
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.
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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 Operating Range(2) Supply Voltage(3) Supply Current Supply Current at Sleep Mode(4) Operating Temperature Range Acceleration Range, X-Axis, Y-Axis, Z-Axis g-Select1 & 2: 00 g-Select1 & 2: 10 g-Select1 & 2: 01 g-Select1 & 2: 11 Output Signal Zero g (TA = 25°C, VDD = 3.3 V)(5) Zero g(4) 1.5g 2g 4g 6g Sensitivity(4) Bandwidth Response XY Z Noise RMS (0.1 Hz – 1 kHz)(4) Power Spectral Density RMS (0.1 Hz – 1 kHz)(4) Control Timing Power-Up Response Time(6) Enable Response Time(7) Sensing Element Resonant Frequency XY Z Internal Sampling Frequency Output Stage Performance Full-Scale Output Range (IOUT = 30 ?A) Nonlinearity, XOUT, YOUT, ZOUT Cross-Axis Sensitivity(8) VFSO NLOUT VXY, XZ, YZ VSS+0.25 –1.0 — — — — VDD–0.25 +1.0 5.0 V %FSO % fGCELL fGCELL fCLK — — — 6.0 3.4 11 — — — kHz kHz kHz tRESPONSE tENABLE — — 1.0 0.5 2.0 2.0 ms ms nRMS nPSD — — 4.7 350 — — mVrms ?g/ Hz f-3dB f-3dB — — 350 150 — — Hz Hz Sensitivity (TA = 25°C, VDD = 3.3 V) S1.5g S2g S4g S6g S,TA 740 555 277.5 185 — 800 600 300 200 ±0.03 860 645 322.5 215 — mV/g mV/g mV/g mV/g %/°C VOFF VOFF, TA 1.485 — 1.65 ±2.0 1.815 — V mg/°C gFS gFS gFS gFS — — — — ±1.5 ±2.0 ±4.0 ±6.0 — — — — g g g g VDD IDD IDD TA 2.2 — — –20 3.3 500 3.0 — 3.6 800 10 +85 V ?A ?A °C Symbol Min Typ Max Unit
1. For a loaded output, the measurements are observed after an RC filter consisting of a 1.0 k? resistor and a 0.1 ?F 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. The response time between 10% of full scale Vdd input voltage and 90% of the final operating output voltage. 7. The response time between 10% of full scale Sleep Mode input voltage and 90% of the final operating output voltage. 8. 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 OPERATION
The Freescale accelerometer is a surface-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 (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 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 1.5g, 2g, 4g, or 6g 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 g-Select2 pins can be left unconnected for applications requiring only a 1.5g sensitivity as the device has an internal pull-down to keep it at that sensitivity (800mV/g). Table 3. g-Select pin Descriptions
g-Select2 0 0 1 1 g-Select1 0 1 0 1 g-Range 1.5g 2g 4g 6g Sensitivity 800 mV/g 600 mV/g 300 mV/g 200 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 12 (Sleep Mode) will place the device in this mode and reduce the current to 3 ?A typ. For lower power consumption, it is recommended to set g-Select1 and g-Select2 to 1.5g mode. By placing a high input signal on pin 12, the device will resume to normal mode of operation. Filtering The 3 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.
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Pin Descriptions Top View
XOUT YOUT ZOUT N/C POWER SUPPLY
16 15 g-Select1 g-Select2 VDD VSS 1 2 3 4 5 N/C 6 N/C
14 13 12 11 10 9 7 N/C 8 N/C Sleep Mode N/C Accelerometer N/C N/C VDD VSS Sleep Mode g-Select1 g-Select2 XOUT YOUT ZOUT Description R C R C R C C C VRH P0 P1 P2 A/DIN A/DIN A/DIN Microcontroller VDD VSS C
Figure 4. Pinout Description Table 4. Pin Descriptions
Pin No. 1 2 3 4 5-7 8 - 11 12 13 14 15 16 Pin Name g-Select1 g-Select2 VDD VSS N/C N/C Sleep Mode ZOUT YOUT XOUT N/C Logic input pin to select g level. Logic input pin to select g level. Power Supply Input Power Supply Ground No internal connection. Leave unconnected. Unused for factory trim. Leave unconnected. Logic input pin to enable product or Sleep Mode. Z direction output voltage. Y direction output voltage. X direction output voltage. No internal connection. Leave unconnected.
Figure 6. Recommended PCB Layout for Interfacing Accelerometer to Microcontroller NOTES: 1. Use 0.1 ?F capacitor on VDD to decouple the power source. Do not exceed capacitor values of 2.2 or 3.3 ?F. 2. Physical coupling distance of the accelerometer to the microcontroller should be minimal. 3. The flag underneath the package is internally connected to ground. It is not recommended for the flag to be soldered down. 4. 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. 5. Use an RC filter with 1.0 k? and 0.1 ?F on the outputs of the accelerometer to minimize clock noise (from the switched capacitor filter circuit). 6. PCB layout of power and ground should not couple power supply noise. 7. Accelerometer and microcontroller should not be a high current path. 8. 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 (11 kHz for the sampling frequency). This will prevent aliasing errors. 9. PCB layout should not run traces or vias under the QFN part. This could lead to ground shorting to the accelerometer flag.
1 k? 0.1 ?F
2 g-Select2 MMA7260QT 3 VDD YOUT 14
1 k? 0.1 ?F
0.1 ?F 4 12 Logic Input VSS Sleep Mode XOUT 15
1 k? 0.1 ?F
Figure 5. Accelerometer with Recommended Connection Diagram
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DYNAMIC ACCELERATION Top View
16 1 15 14 13 12
3 4 5 6 7 8
: Arrow indicates direction of mass movement. 16-Pin QFN Package
STATIC ACCELERATION Top View
Direction of Earth’s gravity field.*
XOUT@ 0g = 1.65 V YOUT @ -1g = 0.85 V ZOUT@ 0g = 1.65 V
XOUT @ 0g = 1.65 V YOUT @ 0g = 1.65 V ZOUT@ +1g = 2.45 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 = 1.65 V
XOUT @ 0g = 1.65 V YOUT @ 0g = 1.65 V ZOUT@ -1g = 0.85 V
XOUT @ 0g = 1.65 V YOUT @ +1g = 2.45 V ZOUT@ 0g = 1.65 V * When positioned as shown, the Earth’s gravity will result in a positive 1g output.
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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. The flag underneath the package is internally connected to ground. It is not recommended for the flag to be soldered down.
6.0 0.55 12 4.25 9
8 1.00 1 4 Flag Solder areas Non-Solder areas 5
Pin 1 ID (non metallic)
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CASE 1622-02 ISSUE B 16-LEAD QFN
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MMA7260QT Rev. 0 10/2006