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ADXL202AQC-1 数据手册 - ADI（亚德诺）

制造商:

ADI（亚德诺）

分类:

加速度传感器

封装:

14-CerPak

Pictures:

3D模型

符号图

焊盘图

引脚图

产品图

页面导航:

原理图在P1P7

封装尺寸在P11

功能描述在P1

技术参数、封装参数在P2

应用领域在P1P2P6P10

6 应用领域

导航目录

原理图在P1 P7
封装尺寸在P11
功能描述在P1
技术参数、封装参数在P2
应用领域在P1 P2 P6 P10

ADXL202AQC-1数据手册

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ADXL202/ADXL210

REV. B

–6–

DEFINITIONS

T1 Length of the “on” portion of the cycle.

T2 Length of the total cycle.

Duty Cycle Ratio of the “on” time (T1) of the cycle to the total

cycle (T2). Defined as T1/T2 for the ADXL202/

ADXL210.

Pulsewidth Time period of the “on” pulse. Defined as T1 for

the ADXL202/ADXL210.

THEORY OF OPERATION

The ADXL202/ADXL210 are complete dual axis acceleration

measurement systems on a single monolithic IC. They contain a

polysilicon surface-micromachined sensor and signal condition-

ing circuitry to implement an open loop acceleration measure-

ment architecture. For each axis, an output circuit converts the

analog signal to a duty cycle modulated (DCM) digital signal

that can be decoded with a counter/timer port on a micropro-

cessor. The ADXL202/ADXL210 are capable of measuring

both positive and negative accelerations to a maximum level of

±2 g or ±10 g. The accelerometer measures static acceleration

forces such as gravity, allowing it to be used as a tilt sensor.

The sensor is a surface micromachined polysilicon structure

built on top of the silicon wafer. Polysilicon springs suspend the

structure over the surface of the wafer and provide a resistance

against acceleration forces. Deflection of the structure is mea-

sured using a differential capacitor that consists of independent

fixed plates and central plates attached to the moving mass. The

fixed plates are driven by 180° out of phase square waves. An

acceleration will deflect the beam and unbalance the differential

capacitor, resulting in an output square wave whose amplitude

is proportional to acceleration. Phase sensitive demodulation

techniques are then used to rectify the signal and determine the

direction of the acceleration.

The output of the demodulator drives a duty cycle modulator

(DCM) stage through a 32 kΩ resistor. At this point a pin is

available on each channel to allow the user to set the signal

bandwidth of the device by adding a capacitor. This filtering

improves measurement resolution and helps prevent aliasing.

After being low-pass filtered, the analog signal is converted to a

duty cycle modulated signal by the DCM stage. A single resistor

sets the period for a complete cycle (T2), which can be set be-

tween 0.5 ms and 10 ms (see Figure 12). A 0 g acceleration

produces a nominally 50% duty cycle. The acceleration signal

can be determined by measuring the length of the T1 and T2

pulses with a counter/timer or with a polling loop using a low

cost microcontroller.

An analog output voltage can be obtained either by buffering the

signal from the X

FILT

and Y

FILT

pin, or by passing the duty cycle

signal through an RC filter to reconstruct the dc value.

The ADXL202/ADXL210 will operate with supply voltages as

low as 3.0 V or as high as 5.25 V.

) = (T1/T2 – 0.5)/12.5%

= 50% DUTY CYCLE

T2(s) = R

SET

(V)/125MV

Figure 12. Typical Output Duty Cycle

APPLICATIONS

POWER SUPPLY DECOUPLING

For most applications a single 0.1 µF capacitor, C

, will ad-

equately decouple the accelerometer from signal and noise on

the power supply. However, in some cases, especially where digital

devices such as microcontrollers share the same power supply, digi-

tal noise on the supply may cause interference on the ADXL202/

ADXL210 output. This is often observed as a slowly undulating

fluctuation of voltage at X

FILT

and Y

FILT

. If additional decou-

pling is needed, a 100 Ω (or smaller) resistor or ferrite beads,

may be inserted in the ADXL202/ADXL210’s supply line.

DESIGN PROCEDURE FOR THE ADXL202/ADXL210

The design procedure for using the ADXL202/ADXL210 with a

duty cycle output involves selecting a duty cycle period and a

filter capacitor. A proper design will take into account the appli-

cation requirements for bandwidth, signal resolution and acqui-

sition time, as discussed in the following sections.

The ADXL202/ADXL210 have two power supply (V

) Pins:

13 and 14. These two pins should be connected directly together.

COM

The ADXL202/ADXL210 have two commons, Pins 4 and 7.

These two pins should be connected directly together and Pin 7

grounded.

This pin is to be left open; make no connections of any kind to

this pin.

Decoupling Capacitor C

A 0.1 µF capacitor is recommended from V

to COM for

power supply decoupling.

The ST pin controls the self-test feature. When this pin is set to

, an electrostatic force is exerted on the beam of the acceler-

ometer. The resulting movement of the beam allows the user to

test if the accelerometer is functional. The typical change in

output will be 10% at the duty cycle outputs (corresponding to

800 mg). This pin may be left open circuit or connected to

common in normal use.

Duty Cycle Decoding

The ADXL202/ADXL210’s digital output is a duty cycle modu-

lator. Acceleration is proportional to the ratio T1/T2. The

nominal output of the ADXL202 is:

0 g = 50% Duty Cycle

Scale factor is 12.5% Duty Cycle Change per g

The nominal output of the ADXL210 is:

0 g = 50% Duty Cycle

Scale factor is 4% Duty Cycle Change per g

These nominal values are affected by the initial tolerance of the

device including zero g offset error and sensitivity error.

T2 does not have to be measured for every measurement cycle.

It need only be updated to account for changes due to tempera-

ture, (a relatively slow process). Since the T2 time period is

shared by both X and Y channels, it is necessary only to mea-

sure it on one channel of the ADXL202/ADXL210. Decoding

algorithms for various microcontrollers have been developed.

Consult the appropriate Application Note.

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