AS8500 - Data Sheet

austriamicrosystems

Revision 1.2, 08-Junel-06

www.austriamicrosystems.com

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41

Writing into subregister TRIMBV of TRR changes the absolute value linearly by 5.1 mV per digit as shown in the following graph and described in full

detail in 7.5.7

Trimming the TC value is similarly done by writing into subregister TRIMBTC. Since the TC trimming is also changing the absolute value it is important

to trim the TC first and then the absolute value.

The TC trimming also opens the unique possibility to change the TC-value within the time of reprogramming of the TRR-register (i.e. within µsec) to

allow the compensation of

different TC-values of the external circuitry for different channels.

In addition it can be used for very fast autocalibration of the total TC of a given channel. An external reference voltage is applied to the channel to be

checked. Then all numbers from 0 to 31 are written into subregister TRIMBTC and a reading is done for the input voltage and the internal temperature

as well. The same is repeated at any temperature above RT. From these data the TRIMBTC setting for a minimum drift can be easily calculated.

temperature coefficient as function of TRIMBTC setting

-250

-200

-150

-100

-50

0

50

100

150

200

0

5

10

15

20

25

30

35

setting of subregister TRIMBTC of TRR

change 12.7 ppm/K

per step

as function of temperature

1,16

1,20

1,24

1,28

1,32

1,36

0

5

10

15

20

25

30

content of TRIMBV in bits

75 °C

24 °C