Datasheet

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Software Calibration
1
2
3
4
5
AGND2
CAP
REF
AGND1
+
2.2 µF
200 Ω
V
IN
R1
IN
R2
IN
6
66.5 kΩ
+
2.2 µF
100 Ω
+ 5 V
1
2
3
4
5
AGND2
CAP
REF
AGND1
+
200 Ω
33.2 kΩ
2.2 µF
6
R1
IN
R2
IN
100 Ω
V
IN
+
2.2 µF
1
2
3
4
5
AGND2
CAP
REF
AGND1
+
200 Ω
33.2 kΩ
2.2 µF
6
R1
IN
R2
IN
100 Ω
V
IN
+
2.2 µF
±10 V 0 V to 5 V 0 V to 4 V
No Calibration
ADS8506
SLAS484B – SEPTEMBER 2007 – REVISED DECEMBER 2007
To calibrate the offset and gain in software, no external resistors are required. However, to get the data sheet
specifications for offset and gain, the resistors shown in Figure 43 are necessary. See the No Calibration section
for more details on the external resistors. Refer to Table 8 for the range of offset and gain errors with and without
the external resistors.
Figure 43. Circuit Diagrams (Without Hardware Trim)
Table 8. Range of Offset and Gain Errors With and Without External Resistors
OFFSET ERROR GAIN ERROR
INPUT
RANGE WITH RESISTORS WITHOUT RESISTORS WITH RESISTORS WITHOUT RESISTORS
(V)
RANGE (mV) RANGE (mV) TYP (mV) RANGE (% FS) RANGE (% FS) TYP
-0.4 ≤ G ≤ 0.4 -0.3 ≤ G ≤ 0.5 0.05
± 10 -10 ≤ BPZ ≤ 10 0 ≤ BPZ ≤ 35 15
0.15 ≤ G
(1)
≤ 0.15 -0.1 ≤ G
(1)
≤ 0.2 0.05
-0.4 ≤ G ≤ 0.4 -1.0 ≤ G ≤ 0.1 -0.2
0 to 5 -3 ≤ UPO ≤ 3 -12 ≤ UPO ≤ -3 -7.5
0.15 ≤ G
(1)
≤ 0.1 -0.55 ≤ G
(1)
≤ -0.05 -0.2
-0.4 ≤ G ≤ 0.4 -1.0 ≤ G ≤ 0.1 -0.2
0 to 4 -3 ≤ UPO ≤ 3 -10.5 ≤ UPO ≤ -1.5 -6
-0.15 ≤ G
(1)
≤ 0.15 -0.55 ≤ G
(1)
≤ -0.05 -0.2
(1) High grade
Figure 43 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 considered when choosing the accuracy and drift specifications of the external resistors. In most applications,
1% metal-film resistors are sufficient.
The external resistors, see Figure 43 , may not be necessary in some applications. These resistors provide
compensation for an internal adjustment of the offset and gain which allows calibration with a single supply. Not
using the external resistors results in offset and gain errors in addition to those listed in the electrical
characteristics section. Offset refers to the equivalent voltage of the digital output when converting with the input
grounded. A positive gain error occurs when the equivalent output voltage of the digital output is larger than the
analog input. Refer to Table 8 for nominal ranges of gain and offset errors with and without the external resistors.
Refer to Figure 44 for typical shifts in the transfer functions which occur when the external resistors are removed.
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