Datasheet

ADS7806
13
SBAS021B
www.ti.com
OFFSET ADJUST GAIN ADJUST
INPUT RANGE RANGE (mV) RANGE (mV)
±10V ±15 ±60
0 to 5V ±4 ±30
0 to 4V ±3 ±30
TABLE VI. Offset and Gain Adjust Ranges for Hardware
Calibration (see Figure 7a).
±10V 0V-5V 0V-4V
FIGURE 7b. Circuit Diagrams (Without Hardware Trim).
±10V 0V-5V 0V-4V
FIGURE 7a. Circuit Diagrams (With Hardware Trim).
each input range (see Figure 8). The input resistor divider
network provides inherent over-voltage protection to at least
±12V on R1
IN
and ±5.5V on R2
IN
.
Analog inputs above or below the expected range will yield
either positive full-scale or negative full-scale digital outputs,
respectively. There will be no wrapping or folding over for
analog inputs outside the nominal range.
CALIBRATION
HARDWARE CALIBRATION
To calibrate the offset and gain of the ADS7806 in hardware,
install the resistors shown in Figure 7a. Table VI lists the
hardware trim ranges relative to the input for each input range.
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
are necessary. See the No Calibration section for more
details on the external resistors. Refer to Table VII for the
range of offset and gain errors with and without the external
resistors.
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-
200Ω
1
2
3
4
5
6
AGND2
REF
CAP
R2
IN
AGND1
R1
IN
+
+
2.2µF
2.2µF
1MΩ
+5V
50kΩ
+5V
100Ω
33.2kΩ
50kΩ
V
IN
200Ω
1
2
3
4
5
6
AGND2
REF
CAP
R2
IN
AGND1
R1
IN
+
+
2.2µF
2.2µF
1MΩ
+5V
50kΩ
50kΩ
33.2kΩ
100Ω
V
IN
200Ω
1
2
3
4
5
6
AGND2
REF
CAP
R2
IN
AGND1
R1
IN
+
+
2.2µF
2.2µF
33.2kΩ
100Ω
V
IN
1MΩ
+5V
50kΩ
50kΩ
200Ω
1
2
3
4
5
6
AGND2
REF
CAP
R2
IN
AGND1
R1
IN
+
+
2.2µF
2.2µF
100Ω
+5V
66.5kΩ
V
IN
200Ω
1
2
3
4
5
6
AGND2
REF
CAP
R2
IN
AGND1
R1
IN
+
+
2.2µF
2.2µF
33.2kΩ
100Ω
V
IN
200Ω
1
2
3
4
5
6
AGND2
REF
CAP
R2
IN
AGND1
R1
IN
+
+
2.2µF
2.2µF
33.2kΩ
100Ω
V
IN