Datasheet

SRC
-+
IN0 (+)
ADC128D818
IN1 (-)
IN3 (+)
IN2 (-)
IN7 (+)
IN6 (-)
IN4 (+)
IN5 (-)
SRC
-+
IN0
ADC128D818
IN1
IN2
IN3
IN6
IN7
IN4
IN5
GND
ADC128D818
SNAS483E –FEBRUARY 2010–REVISED MARCH 2013 www.ti.com
Figure 24. Single-Ended Configuration
Pseudo-Differential Input
Pseudo-differential mode is defined as the positive input voltage applied differentially to the ADC128D818, as
shown in Figure 25. The input that is digitized is (ΔVIN = IN+ - IN-), where (IN+ - IN-) is (IN0-IN1), (IN3-IN2),
(IN4-IN5), or (IN7-IN6). Be aware of this input configuration because the order is swapped. In theory, ΔVIN can
be of any value between 0V and (VREF-3LSb/2),where LSb = VREF/2
12
.
By using this pseudo-differential input, small signals common to both inputs are rejected. Thus, operation with a
pseudo-differential input signal will provide better performance than with a single-ended input. Refer to the
Table 3 section for more information.
Figure 25. Pseudo-Differential Configuration
Modes of Operation
ADC128D818 allows 4 modes of operation, as summarized in the following table. Set the desired mode of
operation using the Advanced Configuration Register — Address 0Bh, bits [2:1]).
Table 3. Modes of Operation
Ch. Mode 0 Mode 1 Mode 2 Mode 3
1 IN0 IN0 IN0 (+) & IN1 (-) IN0
2 IN1 IN1 IN3 (+) & IN2 (-) IN1
3 IN2 IN2 IN4 (+) & IN5 (-) IN2
4 IN3 IN3 IN7 (+) & IN6 (-) IN3
5 IN4 IN4 IN4 (+) & IN5 (-)
6 IN5 IN5 IN7 (+) & IN6 (-)
7 IN6 IN6
8 nc
(1)
IN7
Local Temp Yes No Yes Yes
(1) nc = No Connect
DIGITAL OUTPUT (D
OUT
)
The digital output code for a 12-bit ADC can be calculated as:
D
OUT
= [ΔVIN / VREF] x 2
12
(1)
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