AS8501 - Data Sheet

austriamicrosystems

Revision 1.1, 04-April-06

www.austriamicrosystems.com

Page 23 of 40

subregister TRIMA

change of amplifier offset with TRIMA bits

The offset of the PGA should be trimmed to a mimimum absolute value to guarantee the

full dynamic range with all gain settings.

Nr.

trima0

Notes

trimas

trima3

trima2

trima1

mV

0

0

0

0

0

0

Uos

1),2) ,3)

1

0

0

0

0

1

Uos -1*1.34

1),2)

2

0

0

0

1

0

Uos -2*1.34

1),2)

..

..

..

..

..

..

..

14

0

1

1

1

0

Uos –14*1.34

1),2)

15

0

1

1

1

1

Uos –15*1.34

1),2)

16

1

0

0

0

0

Uos

1),2)

17

1

0

0

0

1

Uos +1*1.34

18

1

0

0

1

0

Uos +2*1.34

1),2)

..

..

..

..

..

..

..

30

1

1

1

1

0

Uos +14*1.34

1),2)

31

1

1

1

1

1

Uos +15*1.34

Notes:

1)

Uos is the input offset voltage in mV at TRIMA = 00000

2)

Every step of TRIMA settings brings

$offset=1.34 mV change in absolute value of the input offset voltage.

If the measured value is Uos then the number that should be written into the TRIMA for minimum

final absolute value is calculated as TRIMA=int((Uos)/1.34) for Uos above zero and

TRIMA=16+int(-Uos)/1.34) for Uos below zero.

3)

The input offset voltage can be measured with chopping and dechopping bits being cleared in register CRG.

Any input channel as well as gain settings can be used. The input should be shorted to avoid any external voltages to interfere with the

measurement. If the measured output voltage is Va then the offset voltage is calculated acc. Vos = Va/gain.

subregister TRIMBV

change of reference voltage Uo with TRIMBV bits

Nr.

trimbv0

Notes

trimbvs

trimbv3

trimbv2

trimbv1

mV

0

0

0

0

0

0

Ua

1),2)

1

0

0

0

0

1

Ua -1*5.1

1),2)

2

0

0

0

1

0

Ua -2*5.1

1),2)

..

..

..

..

..

..

..

14

0

1

1

1

0

Ua –14*5.1

1),2)

15

0

1

1

1

1

Ua –15*5.1

1),2)

16

1

0

0

0

0

Ua

1),2)

17

1

0

0

0

1

Ua +1*5.1

18

1

0

0

1

0

Ua +2*5.1

1),2)

..

..

..

..

..

..

..

30

1

1

1

1

0

Ua +14*5.1

1),2)

31

1

1

1

1

1

Ua +15*5.1

Notes:

1)

Ua is the reference voltage in mV at TRIMBTC = 00000, the optimum value is 1.232V.

2)

Every step of TRIMBV settings brings

For trimming the TC value and absolute value of the reference voltage it is recommended to trim the TC

value first and then trim the absolute value since TRIMBTC is changing both TC and absolute value, whereas

TRIMBV is changing only the absolute value.

If the measured absolute value is Uam then the number that should be written into the TRIMBV for optimum

final absolute value is calculated as TRIMBV=int((Uam-1.231)/0.0051) for Uam above the ideal value and

TRIMBV=16+int(-(Uam-1.232)/0.0051) for Uam below the ideal value.