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ADC1205 View Datasheet(PDF) - National ->Texas Instruments

Part NameDescriptionManufacturer
ADC1205 12-Bit Plus Sign ?P Compatible A/D Converters National-Semiconductor
National ->Texas Instruments National-Semiconductor
ADC1205 Datasheet PDF : 18 Pages
First Prev 11 12 13 14 15 16 17 18
Functional Description (Continued)
A simpler although slightly less accurate approach is to
ground VIN(a) and VIN(b) and adjust for all zeros at the
output Error will be well under LSB if the adjustment is
done so that the potentiometer is ‘‘centered’’ within the
0 000 000 range A positive voltage at the VOS input will
reduce the output code The adjustment range is a4 to
b30 LSB
TL H 5676–11
FIGURE 15 Zero Adjust Circuit
7 2 POSITIVE AND NEGATIVE FULL-SCALE
ADJUSTMENT
Unipolar Inputs
Apply a differential input voltage which is 1 5 LSB below the
desired analog full-scale voltage (VF) and adjust the magni-
Typical Applications
tude of the VREF input so that the output code is just chang-
ing from 0 1111 1111 1110 to 0 1111 1111 1111
Bipolar Inputs
Do the same procedure outlined above for the unipolar case
and then change the differential input voltage so that the
digital output code is just changing from 1 0000 0000 0001
to 1 0000 0000 0000 Record the differential input voltage
VX the ideal differential input voltage for that transition
should be
 J bVF
a
VF
8192
Calculate the difference between Vx and the ideal voltage
 J D e VX b
bVF
a
VF
8192
Then apply a differential input voltage of
 JD
VX b 2
and adjust the magnitude of VREF so the digital output
code is just changing from 1 0000 0000 0001 to
1 0000 0000 0000 That will obtain the positive and negative
full-scale transition with symmetrical minimum error
Input must have some
current return path to
signal ground
TL H 5676 – 12
14
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