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ADC08038 View Datasheet(PDF) - National ->Texas Instruments

Part NameDescriptionManufacturer
ADC08038 8-Bit High-Speed Serial I/O A/D Converters with Multiplexer Options, Voltage Reference, and Track/Hold Function National-Semiconductor
National ->Texas Instruments National-Semiconductor
ADC08038 Datasheet PDF : 24 Pages
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Functional Description (Continued)
put 0000 0000 digital code for this minimum input voltage by
biasing any VIN (−) input at this VIN(MIN) value. This utilizes
the differential mode operation of the A/D.
The zero error of the A/D converter relates to the location of
the first riser of the transfer function and can be measured by
grounding the VIN (−) input and applying a small magnitude
positive voltage to the VIN (+) input. Zero error is the differ-
ence between the actual DC input voltage which is neces-
sary to just cause an output digital code transition from 0000
0000 to 0000 0001 and the ideal 12 LSB value (12 LSB =
9.8mV for VREF = 5.000VDC).
5.2 Full Scale
The full-scale adjustment can be made by applying a differ-
ential input voltage which is 112 LSB down from the desired
analog full-scale voltage range and then adjusting the mag-
nitude of the VREFIN input (or VCC for the ADC08032) for a
digital output code which is just changing from 1111 1110 to
1111 1111.
5.3 Adjusting for an Arbitrary Analog Input
Voltage Range
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 12 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 tran-
The full-scale adjustment should be made [with the proper
VIN (−) voltage applied] by forcing a voltage to the VIN (+) in-
put 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 ad-
justment procedure.
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