Datasheet
ADC1213X
V
A
+
LM4040-2.5
(LM4041-1.2)
430:
+5.0V
(+3.3V)
V
D
+
V
REF
+
V
REF
-
+2.5V
(+1.25V)
DGNDAGND
ANALOG INPUT VOLTAGE
GROUND REFERENCE
CH0
CH1
CH2
to
CH7
COM
ANALOG INPUT
VOLTAGE RANGE
0V to 5V
(0V to 2.5V)
12-BITS SIGNED
ASSIGNED
(+) INPUT
ASSIGNED
(-) INPUT
R2
600:
R1
(DEPENDS UPON
ACQUISITION TIME)
0.01 uF 0.1 uF 10 uF
0.01 uF 0.1 uF 10 uF
0.01 uF 0.1 uF 10 uF
ADC1213X
V
A
+
0.01 uF 0.1 uF 10 uF
LM4040-4.1
(LM4040-2.5)
1k
+5.0V
(+3.3V)
V
D
+
V
REF
+
V
REF
-
+2.048V
(+2.5)
DGNDAGND
ANALOG INPUT VOLTAGE
GROUND REFERENCE
CH0
CH1
CH2
to
CH7
COM
ASSIGNED
(+) INPUT
ASSIGNED
(-) INPUT
ANALOG INPUT
VOLTAGE RANGE
0 TO 4.096V
(0V TO 2.5V)
12-BITS UNSIGNED
0.01 uF 0.1 uF 10 uF
0.01 uF 0.1 uF 10 uF
ADC12130, ADC12132, ADC12138
www.ti.com
SNAS098G –MARCH 2000–REVISED MARCH 2013
Figure 69. Single-Ended Biasing
For pseudo-differential signed operation, the circuit of Figure 70 shows a signal AC coupled to the ADC. This
gives a digital output range of −4096 to +4095. With a 2.5V reference, 1 LSB is equal to 610 μV. Although the
ADC is not production tested with a 2.5V reference, when V
A
+
and V
D
+
are +5.0V, linearity error typically will not
change more than 0.1 LSB (see the curves in Typical Performance Characteristics). With the ADC set to an
acquisition time of 10 clock periods, the input biasing resistor needs to be 600Ω or less. Notice though that the
input coupling capacitor needs to be made fairly large to bring down the high pass corner. Increasing the
acquisition time to 34 clock periods (with a 5 MHz CCLK frequency) would allow the 600Ω to increase to 6k,
which would set the high pass corner at 26 Hz. Increasing R, to 6k would allow R
2
to be 2k with a 1 μF coupling
capacitor.
Figure 70. Pseudo-Differential Biasing with the Signal Source AC Coupled Directly into the ADC
An alternative method for biasing pseudo-differential operation is to use the +2.5V from the LM4040 to bias any
amplifier circuits driving the ADC as shown in Figure 71. The value of the resistor pull-up biasing the LM4040-2.5
will depend upon the current required by the op amp biasing circuitry.
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