ADuCM310 Hardware Reference Manual
UG-549
Rev. C | Page 21 of 192
O
U
T
P
U
T
C
O
D
E
VOLT AGE INPUT
0000 1111 1111 1111 1111
0000 1111 1111 1111 1110
0000 1111 1111 1111 1101
0000 1111 1111 1111 1100
0000 0000 0000 0000 0011
1LSB
0V
V
REF
– 1LSB
0000 0000 0000 0000 0010
0000 0000 0000 0000 0001
0000 0000 0000 0000 0000
1LSB =
V
REF
65536
ADCDATx[31:12]
1
1461-
006
Figure 6. ADC Transfer Function: Single-Ended Mode
Differential Mode
The amplitude of the differential signal is the difference between the signals applied to the positive and negative AINx pins (that is,
AIN+ − AIN−). The maximum amplitude of the differential signal is, therefore, −V
REF
to +V
REF
p-p (2 × V
REF
). This is regardless of the
common mode (CM). The common mode is the average of the two signals (AIN+ + AIN−)/2, and is, therefore, the voltage that the two
inputs are centered on. This results in the span of each input being CM ± V
REF
/2. This voltage must be set up externally, and its range
varies with V
REF
. The voltage at the positive and negative AINx pins must be within the allowed input voltage range.
The output coding is twos complement in fully differential mode, with
1 LSB = 2 V
REF
/65,536
Or
2 × 2.5 V/65,536 = 76.29 µV
where V
REF
= 2.5 V.
The ideal input/output transfer characteristic is shown in Figure 7.
VOLTAGE INPUT (V
IN
+ – V
IN
–)
O
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P
U
T
C
O
D
E
0000 0000 1111 1111 1110
0000 0000 1111 1111 1100
0000 0000 1111 1111 1010
0000 0000 0000 0000 0010
0000 0000 0000 0000 0000
1111 1111 1111 1111 1110
1111 0000 0000 0000 0100
1111 0000 0000 0000 0010
1111 0000 0000 0000 0000
1LSB =
2 × V
REF
65536
ADCDATx[31:12]
–V
REF
+ 1LSB
+V
REF
– 1LSB
0LSB
1
1461-
007
Figure 7. ADC Transfer Function: Differential Mode