used for each input range (see Figure 8). The input resistor
divider network provides inherent over-voltage protection to
at least
±5.5V
for R2
IN
and
±12V
for R1
IN
.
Analog inputs above or below the expected range will yield
either positive full-scale or negative full-scale digital outputs,
respectively. Wrapping or folding over for analog inputs
outside the nominal range will not occur.
INPUT RANGE
±10V
0 to 5V
0 to 4V
OFFSET ADJUST
RANGE (mV)
±15
±4
±3
GAIN ADJUST
RANGE (mV)
±60
±30
±30
TABLE VI. Offset and Gain Adjust Ranges for Hardware
Calibration (see Figure 7a).
are necessary. See the No Calibration section for more
details on the external resistors. Refer to Table VIII for the
range of offset and gain errors with and without the external
resistors.
CALIBRATION
HARDWARE CALIBRATION
To calibrate the offset and gain of the ADS7807 in hardware,
install the resistors shown in Figure 7a. Table VI lists the
hardware trim ranges relative to the input for each input
range.
NO CALIBRATION
Figure 7b shows circuit connections. Note that the actual
voltage dropped across the external resistors is at least two
orders of magnitude lower than the voltage dropped across
the internal resistor divider network. This should be consid-
SOFTWARE CALIBRATION
To calibrate the offset and gain in software, no external
resistors are required. However, to get the data sheet speci-
fications for offset and gain, the resistors shown in Figure 7b
±
10V
0V-5V
0V-4V
33.2kΩ
200Ω
V
IN
200Ω
1
R1
IN
1
R1
IN
1
200Ω
V
IN
2
R1
IN
2
AGND1
33.2kΩ
2
AGND1
AGND1
3
100Ω
33.2kΩ
+5V
50kΩ
50kΩ
+5V
1MΩ 2.2µF
+
6
2.2µF
4
+
5
R2
IN
V
IN
+5V
100Ω
3
R2
IN
3
+5V
100Ω
4
2.2µF
+
5
50kΩ
1MΩ 2.2µF
+
6
50kΩ
R2
IN
CAP
4
2.2µF
50kΩ
+
5
1MΩ 2.2µF
+
6
CAP
CAP
REF
50kΩ
AGND2
REF
REF
AGND2
AGND2
FIGURE 7a. Circuit Diagrams (With Hardware Trim).
±
10V
0V-5V
33.2kΩ
0V-4V
200Ω
V
IN
1
200Ω
R1
IN
1
R1
IN
200Ω
V
IN
1
R1
IN
2
66.5kΩ
+5V
100Ω
4
2.2µF
+
5
2.2µF
+
6
AGND1
33.2kΩ
2
AGND1
2
AGND1
3
R2
IN
V
IN
100Ω
3
R2
IN
100Ω
3
R2
IN
CAP
2.2µF
4
+
5
2.2µF
+
6
CAP
4
2.2µF
+
5
2.2µF
+
6
CAP
REF
REF
REF
AGND2
AGND2
AGND2
FIGURE 7b. Circuit Diagrams (Without Hardware Trim).
ADS7807
SBAS022C
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13
BURR-BROWN [ BURR-BROWN CORPORATION ]
