ADC08138CIWM datasheet(16/21 Pages) NSC

Part #	ADC08138CIWM

Description	8-Bit High-Speed Serial I/O A/D Converters with Multiplexer Options, Voltage Reference, and Track/Hold Function

PDF	21 Pages

Scroll/Zoom	100%

Manufacturer	NSC [National Semiconductor (TI)]

Direct Link	http://www.national.com

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16 / 21 page

Functional Description (Continued)

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 V

IN (+) 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 00

HEX to 01HEX code tran-

sition.

The full-scale adjustment should be made [with the proper

IN (−) voltage applied] by forcing a voltage to the VIN (+) in-

put which is given by:

where:

MAX = the high end of the analog input range

and

MIN = the low end (the offset zero) of the analog range.

(Both are ground referenced.)

The V

REFIN (or VCC) voltage is then adjusted to provide a

code change from FE

HEX to FFHEX. This completes the ad-

justment procedure.

Applications

A “Stand-Alone” Hook-Up for ADC08138 Evaluation

DS010749-45

*Pinouts shown for ADC08138.

For all other products tie to pin functions as shown.

ADC08138CIWM Datasheet(PDF) 16 Page - National Semiconductor (TI)