Datasheet

18
ADS1250
®
SOFTWARE GAIN
The excellent performance, flexibility, and low cost of the
ADS1250 allows the converter to be considered for designs
which would not normally need a 20-bit ADC. For example,
many designs utilize a 12-bit converter and a high gain INA
or PGA for digitizing low amplitude signals. For some of these
applications, the ADS1250 by itself may be a solution. The
digital result of the converter can simply be shifted up by “n”
bits in the main controller, resulting in a gain of “n” times G,
where G is the gain setting. While this type of manipulation of
the output data is obvious, it is easy to miss how much the gain
can be increased in this manner on a 20-bit converter. For
example, shifting the result by 4 bits when the ADS1250 is set
to a gain of 8 results in an effective gain of 128.
Isolation
The serial interface of the ADS1250 provides for simple
isolation methods. An example of an isolated four-wire
interface is shown in Figure 19. The ISO150 is used to
transmit the digital clocks over the isolation barrier. In
addition, the digital output of the ADS1250 can, in some
cases, drive opto-isolators directly. Note that DOUT is tri-
stated for the majority of the conversion period and the opto-
isolator connection must take this into account.
FIGURE 24. Isolated Four-Wire Interface.
+V
IN
–V
IN
AGND
+V
S
V
REF
DSYNC
+V
D
DGND
DGND
G1
G0
CS
DRDY
CLK
SCLK
DOUT
V
DD1
V
REF
Circuit
AGND
AV
DD
DGND
ISO150
D
1A
R/T
1A
V
SA
G
B
R/T
1B
D
1B
D
2A
R/T
2A
G
A
V
SB
R/T
2B
D
2B
V
DD2
V
DD1
V
DD1
V
DD2
DGND
DGND
DGND
AGND
DOUT
SCLK
V
DD2
V
DD1
V
DD2
DGND
DGND
DGND
AGND
CLK
DRDY
ISO150
D
1A
R/T
1A
V
SA
G
B
R/T
1B
D
1B
D
2A
R/T
2A
G
A
V
SB
R/T
2B
D
2B
ADS1250