ADI采用3轴数字加速度计的ADXL345血压计解决方案

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* ADI ADXL345血压计解决方案

ADI公司的血压计解决方案采用3轴±2 g/±4 g/±8 g/±16 g 数字加速度计ADXL345,12位电容-数字转换器AD7152/AD7153, 全速/低速USB数字绝缘器ADuM4160,单电极容性传感器CapTouch可编程控制器AD7147,以及带低部端口和数字输出的iMEMS麦克风ADMP421等器件.本文介绍了血压计解决方案方框图,以及所采用的主要元器件的主要特性,方框图和应用电路等.

图1.电子血压计方框图

主要元器件介绍:

ADXL345: 3-Axis, ±2 g/±4 g/±8 g/±16 g Digital Accelerometer

The ADXL345 is a small, thin, low power, 3-axis accelerometer with high resolution (13-bit) measurement at up to ±16 g. Digital output data is formatted as 16-bit twos complement and is acces-sible through either a SPI (3- or 4-wire) or I2C digital interface.

The ADXL345 is well suited for mobile device applications. It measures the static acceleration of gravity in tilt-sensing appli-cations, as well as dynamic acceleration resulting from motion or shock. Its high resolution (4 mg/LSB) enables measurement of inclination changes less than 1.0°.

Several special sensing functions are provided. Activity and inactivity sensing detect the presence or lack of motion and if the acceleration on any axis exceeds a user-set level. Tap sensing detects single and double taps. Free-fall sensing detects if the device is falling. These functions can be mapped to one of two interrupt output pins. An integrated, patent pending 32-level first in, first out (FIFO) buffer can be used to store data to minimize host processor intervention.

Low power modes enable intelligent motion-based power management with threshold sensing and active acceleration measurement at extremely low power dissipation.

The ADXL345 is supplied in a small, thin, 3 mm × 5 mm × 1 mm, 14-lead, plastic package.

ADXL345主要特性:

Ultralow power: as low as 40 μA in measurement mode and 0.1 μA in standby mode at VS = 2.5 V (typical)

Power consumption scales automatically with bandwidth

User-selectable resolution

Fixed 10-bit resolution

Full resolution, where resolution increases with g range, up to 13-bit resolution at ±16 g (maintaining 4 mg/LSB scale factor in all g ranges)

Embedded, patent pending FIFO technology minimizes host processor load

Tap/double tap detection

Activity/inactivity monitoring

Free-fall detection

Supply voltage range: 2.0 V to 3.6 V

I/O voltage range: 1.7 V to VS

SPI (3- and 4-wire) and I2C digital interfaces

Flexible interrupt modes mappable to either interrupt pin

Measurement ranges selectable via serial command

Bandwidth selectable via serial command

Wide temperature range (?40℃ to +85℃)

10,000 g shock survival

Pb free/RoHS compliant

Small and thin: 3 mm × 5 mm × 1 mm LGA package

ADXL345应用:

Handsets

Medical instrumentation

Gaming and pointing devices

Industrial instrumentation

Personal navigation devices

Hard disk drive (HDD) protection

Fitness equipment

图2. ADXL345方框图

图3.AD7152和AD7153方框图

图4.AD7153差分容性传感器基本应用电路图

Full/Low Speed USB Digital Isolator ADuM4160

The ADuM4160 is a USB port isolator, based on Analog Devices, Inc., iCoupler? technology. Combining high speed CMOS and monolithic air core transformer technology, these isolation components provide outstanding performance characteristics and are easily integrated with low and full speed USB-compatible peripheral devices.

Many microcontrollers implement USB so that it presents only the D+ and D? lines to external pins. This is desirable in many cases because it minimizes external components and simplifies the design; however, this presents particular challenges when isolation is required. USB lines must automatically switch between actively driving D+/D?, receiving data, and allowing external resistors to set the idle state of the bus. The ADuM4160 provides mechanisms for detecting the direction of data flow and control over the state of the output buffers. Data direction is determined on a packet-by-packet basis.