Functional Description (Continued)
Adjusting for an Arbitrary Analog Input
If the analog zero voltage of the A/D is shifted away from
ground (for example, to accommodate an analog input signal
which does not go to ground), this new zero reference
should be properly adjusted first. A VIN (+) voltage which
equals this desired zero reference plus 1⁄2 LSB (where the
LSB is calculated for the desired analog span, using 1 LSB =
analog span/256) is applied to selected “+” input and the
zero reference voltage at the corresponding “−” input should
then be adjusted to just obtain the 00HEX to 01HEX code
The full-scale adjustment should be made [with the proper
VIN (−) voltage applied] by forcing a voltage to the VIN (+)
input which is given by:
VMAX = the high end of the analog input range
VMIN = the low end (the offset zero) of the analog range.
(Both are ground referenced.)
The VREFIN (or VCC) voltage is then adjusted to provide a
code change from FEHEX to FFHEX. This completes the
A “Stand-Alone” Hook-Up for ADC08138 Evaluation
*Pinouts shown for ADC08138.
For all other products tie to pin functions as shown.