MMA766OFC加速度计用于手机

　　MMA766OFC Accelerometer for Mobile Handsets

　　作者：Michelle Kelsey， Laura Salhuana， Mathieu Forget， Nigel Drew

　　Accelerometers are proliferating rapidly in the mobile phone market， enabling clever innovations that continue to help developers differentiate their products from the competition.

　　According to iSuppli， accelerometers are rapidly penetrating the mobile handset market， and there seems to be no letup in the near future. As they predicted， approximately one-third of all mobile phones shipped in 2010 included MEMS accelerometers. That was up from one in five shipped in 2009 and one out of 11 in 2008. Accelerometers allow users to employ finger tapping and three dimensional motion to execute specific commands， often replacing the need for multiple keystrokes.

　　Cell phone users， for instance， are demanding sophisticated user interfaces that allow fast， precise communications without complicated data entry. They also want these capabilities in budget -priced phones as well as in the high-end models. Freescale‘s MMA7660FC low-g， three-axis digital accelerometer is the company’s first to be designed specifically for m obile phones and other small， hand-held appliances. Low-cost， low-power intelligent sensing in a compact package can add tremendous functionality to portable battery-powered devices with no room to spare.

　　Essentially， MEMS combine silicon-based microelectronics with micromachining technology. A three-axis accelerometer can detect motion on three different planes， or axes. This allows developers to implement a single accelerometer to incorporate tap， shake， and orientation detection in a mobile device. For instance， a back-and-forth shake and an up-and-down shake can be used to execute two different commands. Although accelerometers can be used in a number of hand-held applications， mobile phones have dominated the market. Accelerometers not only enable developers to incorporate clever innovations that differentiate their products from the competition， but also to extend revenue opportunities to ISVs （independent software vendors）， interface providers， and wireless service carriers.

　　The MMA7660FC accelerometer can be employed to detect natural user interactions， including：

　　· Orientation detection that goes beyond automatically adjusting to a portrait or landscape configuration

　　· Single-tap detection， which can be configured at user-selectable thresholds and time duration on the X， Y， and Z-axes

　　· Shake， which can be used to represent specific keystrokes or a series of keystrokes

　　· Gesturing and gaming moves， such as three-dimensional tilt， turn， and twist

　　However， portable devices such as mobile phones demand more than improved functionality alone if they want to carve out a profitable piece of the market. The inherent limitations of size and battery life， among others， must also be addressed.

　　Four good reasons to use MMA7660FC accelerometers

　　As more applications require motion detection， the MMA7660FC features four key requirements： digital

　　output， small package， low power consumption， and embedded intelligence.

　　Digital output

　　The MMA7660FC accelerometer has I²C output for communicating directly with the processor， eliminating the need for an ADC. With 6-bit output values of X， Y， or Z， you can configure an interrupt for one or multiple options of motion detection such as orientation， tap， shake， or data ready. Once an interrupt occurs， the processor can then interrogate the accelerometer via the I²C to understand exactly which interrupt has been triggered.

　　Small footprint

　　The MMA7660FC is contained in a 3 x 3 x 0.9 mm dual， flat， no-lead （DFN） package with 0.5 mm pitch. This is critical for portable， handheld devices， such as mobile phones， because it enables designers to add all the useful functionalities of a three-axis accelerometer without straining the limits of a space-constrained PCB.

　　To help ensure proper mounting， Freescale offers an application note， “AN3839： MMA7660FC Board Mounting Guidelines，” available as a PDF download from www.freescale.com/xyz. It discusses the minimum recommended footprint for surface mount applications that can significantly affect the soldering connection interface between the board and the package. The application note also provides soldering and mounting guidelines that will minimize the stress on the package after board mount. Following these guidelines and considerations for board mounting will result in optimal performance from the MMA7660FC sensor.

　　Low-power consumption in end applications

　　Freescale is a recognized leader in the design of high-performance， energy-efficient semiconductor

　　products. Underscoring this， Freescale has introduced the Energy-Efficient Solutions mark. This mark highlights selected products that excel in the effective implementation of energy-efficiency technologies， and that deliver market-leading performance in the application spaces they are designed to address. Visit the latest list of these products.

　　The MMA7660FC accelerometer has earned the Freescale Energy-Efficient Solutions mark through a distinctive combination of advanced architectural and circuit techniques with the latest design methodology and process technology， which deliver energy-efficient performance to provide the highest possible performance levels within a restricted energy budget. This is the result of Freescale working closely with customers in a targeted market to define their specific performance and energy requirements， and developing optimized solutions that yield exceptionally energy-efficient performance for the life of the application. The MMA7660FC accelerometer has very low current consumption： an off mode of 0.4 µA， a standby mode of 2 µA， and an active mode down to 47 µA （1 sample/second）。

　　In addition， the MMA7660FC accelerometer offers extremely flexible performance/power consumption options through user-configurable sample rates. The rates can be adjusted to provide only the performance needed for specific functions， and each configuration corresponds with different current consumption （see Table 1）。