MXR7900DF datasheet(5/6 Pages) MEMSIC

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MEMSIC MXR7900A/C/D Rev.A

Page 5 of 6

4/09/2009

Resolution: The accelerometer resolution is limited by

noise. The output noise will vary with the measurement

bandwidth. With the reduction of the bandwidth, by

applying an external low pass filter, the output noise drops.

Reduction of bandwidth will improve the signal to noise

ratio and the resolution. The output noise scales directly

with the square root of the measurement bandwidth. The

maximum amplitude of the noise, its peak- to- peak value,

approximately defines the worst case resolution of the

measurement. With a simple RC low pass filter, the rms

noise is calculated as follows:

Noise (mg rms) = Noise(mg/ Hz ) *

)

(

Bandwidth

The peak-to-peak noise is approximately equal to 6.6 times

the rms value (for an average uncertainty of 0.1%).

nd SOFTWARE COMPENSATAION

1.Block Diagram

2.Components:

2.1 Temperature Sensor

Any type of sensor which can have at least +/-3

°C

accuracy over -40~125

°C temperature range, one

possible choice is TMP141 from Texas

Instruments.

Also, the temperature sensor need to be mounted

as close as to MXR7900xF part as possible to

sense the temperature correctly.

2.2 Capacitor

C1: Grade higher than X7R, at least 0.22uF

capacitor

C2: 10uF electrolytic, Low-ESR capacitor

Both the two capacitors need to be soldered as

close as to the VDD pin, since the internal heater is

in PWM (1MHz) control mode, with all VDD on the

heater at some portion of the time, by using larger

value capacitor can minimize the induced noise on

the outputs.

2.3 MCU

Anyway type of MCU with 2 of 12bits A/D port is

OK.

Part Identity Reading

3.1 Digital Switching Characteristics

SYMBOL

PARAMETER

MIN

TYP

MAX

UNITS

td7

Rising edge of

CLK to rising

edge of TP

2.0

td8

Rising edge of TP

to valid data out

10.0

STin

Frequency

800

KHz

Note: Total delay time of td7+td8 should be less than half

of cycling time of STin signal to make sure the data can be

read out correctly at the falling edge of the STin signal.

3.2 Digital Parameters

SYM

BOL

PARAMETER

MIN

TYP

MAX

UNITS

VIH

High Level Input Voltage

VDD -.5

Volts

VIL

Low Level Input Voltage

0.5

Volts

IIL

Input Leakage, All Inputs

1.0

VOH

High Level Output Voltage

VDD -.5

Volts

VOL

Low Level Output Voltage

0.5

Volts

3.3 Waveform

3.4 Identity code number

After the first rising edge of the STin, the first bit of the

identity code will be appeared at pin Yout with a time

td8 delay and exists for the whole STin cycle, the

second bit of the identity code will be appeared at pin

Yout after the second rising edge of STin, etc.

There are totally 72bits, MEMSIC will use the 72bits

data to identify each device, and provide its offset,

sensitivity and selftest at 25

°C with the identity code.

MXR7900A

CLK

STin

Yout

Xout

VDD

GND

MCU

A/D

I/O

TEMP

I/O

CLK

STin

Yout

Timing for Identity Code

MXR7900DF Datasheet(PDF) 5 Page - MEMSIC Semiconductor (Tianjin) Co., Ltd.

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