ADC12130CIWM datasheet(33/42 Pages) NSC

Part #	ADC12130CIWM

Description	Self-Calibrating 12-Bit Plus Sign Serial I/O A/D Converters with MUX and Sample/Hold

PDF	42 Pages

Scroll/Zoom	100%

Manufacturer	NSC [National Semiconductor (TI)]

Direct Link	http://www.national.com

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33 / 42 page

Application Information (Continued)

fier circuits driving the ADC as shown in Figure 13. The value

of the resistor pull-up biasing the LM4040-2.5 will depend

upon the current required by the op amp biasing circuitry.

In the circuit of Figure 13 some voltage range is lost since

the amplifier will not be able to swing to +5V and GND with

a single +5V supply. Using an adjustable version of the

LM4041 to set the full scale voltage at exactly 2.048V and a

lower grade LM4040D-2.5 to bias up everything to 2.5V as

shown in Figure 14 will allow the use of all the ADC’s digital

output range of −4096 to +4095 while leaving plenty of head

room for the amplifier.

Fully differential operation is shown in Figure 15. One LSB

for this case is equal to (4.1V/4096)=1mV.

01207940

FIGURE 13. Alternative Pseudo-Differential Biasing

01207941

FIGURE 14. Pseudo-Differential Biasing without the Loss of Digital Output Range

ADC12130CIWM Datasheet(PDF) 33 Page - National Semiconductor (TI)