SCA100T Series

Murata Electronics Oy

Subject to changes

13/17

www.muratamems.fi

Doc. nr. 8261800

Rev.B2































LSB/g

LSB

LSB

arcsin

0

@

Sens

D

D

out

out



where;

digital output (

RDAX or RDAY)

digital offset value, nominal value = 1024



angle

Sens

sensitivity of the device

. (SCA100T-D01: 1638, SCA100T-D02: 819)

As an example following table contains data register values and calculated differential digital

output values with -5, -1 0, 1 and 5 degree tilt angles.

Angle

[°]

Acceleration

[mg]

RDAX (SCA100T-

D01)

RDAX (SCA100T-

D02)

-5

-87.16

dec: 881

bin: 011 0111 0001

dec: 953

bin: 011 1011 1001

-1

-17.45

dec: 995

bin: 011 1110 0011

dec: 1010

bin: 011 1111 0010

0

0

dec: 1024

bin: 100 0000 0000

dec: 1024

bin: 100 0000 0000

1

17.45

dec: 1053

bin: 100 0001 1101

dec: 1038

bin: 100 0000 1110

5

87.16

dec: 1167

bin: 100 1000 1111

dec: 1095

bin: 100 0100 0111

2.6

Self Test and Failure Detection Modes

To ensure reliable measurement results the SCA100T has continuous interconnection failure and

calibration memory validity detection. A detected failure forces the output signal close to power

supply ground or VDD level, outside the normal output range.

The calibration memory validity is verified by continuously running parity check for the control

register memory content. In the case where a parity error is detected, the control register is

automatically re-loaded from the EEPROM. If a new parity error is detected after re-loading data

both analog output voltages are forced to go close to ground level (<0.25 V) and SPI outputs go

below 102 counts.

The SCA100T also includes a separate self test mode. The true self test simulates acceleration, or

deceleration, using an electrostatic force. The electrostatic force simulates acceleration that is high

enough to deflect the proof mass to the extreme positive position, and this causes the output signal

to go to the maximum value. The self test function is activated either by a separate on-off

command on the self test input, or through the SPI. To ensure that output goes to positive end

product must be in 0g position. For position below 0g output change might be limited to +1g

change of the output.

The self-

test generates an electrostatic force, deflecting the sensing element’s proof mass, thus

checking the complete signal path. The true self test performs following checks:



Sensing element movement check



ASIC signal path check



PCB signal path check



Micro controller A/D and signal path check

The created deflection can be seen in both the SPI and analogue output.s The self test function is

activated digitally by a STX or STY command, and de-activated by a MEAS command. Self test

can

be also activated applying logic”1” (positive supply voltage level) to ST pins (pins 9 & 10) of

SCA100T. The self test Input high voltage level is 4

– Vdd+0.3 V and input low voltage level is 0.3

– 1 V. The self test function must not be activated for both channels at the same time.