AS8501 - Data Sheet

austriamicrosystems

Revision 1.1, 04-April-06

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7.2.1

Reference voltage

The ASSP contains a highly sophisticated precision reference voltage. Its typical temperature dependence is a slight parabola shaped curve and is

shown in figure 21. This reference voltage is used mainly for the internal AD-converter, but can also be used for external purposes if the impedance of

the external circuitry is high enough.

The absolute value and its temperature coefficient (TC) is given by the content of the TRR register. This opens the possibility to calibrate the reference

voltage to the optimum absolute value (i.e. 1.28 V) and the TC value to zero thus eliminating fully the production spread.

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.

1,1 6

1,2 0

1,2 4

1,2 8

1,3 2

1,3 6

0

5

1 0

15

20

25

3 0

c onte n t of TR IM B V in bits

75 ° C

24 °C

1,12

1,14

1,16

1,18

1,20

1,22

1,24

1,26

10

30

50

70

90

110

resistan ce lo ad in kO h m

m eas u rem en t

o p en lo o p va lu e

Figure 4: Reference voltage as function of resistance load

Figure 5: Reference voltage as function of temperature