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+ Full-Scale
Digital Output
Analog Input
− Full-Scale
+ Full-Scale
Digital Output
− Full-Scale
Analog Input
(a) Bipolar (b) Unipolar
Typical Transfer Functions With External Resistors.
Typical Transfer Functions Without External Resistors.
V
IN
200 Ω 39.8 kΩ
9.9 kΩ33.5 kΩ
100 Ω
+ 5 V
+ 2.5 V
20 kΩ 40 kΩ
+ 2.5 V
CDAC
(0.3125 V to 2.8125 V)
V
IN
200 Ω 39.8 kΩ
9.9 kΩ
33.5 kΩ
100 Ω
+ 2.5 V
20 kΩ 40 kΩ
+ 2.5 V
CDAC
(0.3125 V to 2.8125 V)
V
IN
200 Ω 39.8 kΩ
9.9 kΩ
33.5 kΩ
100 Ω
+ 2.5 V
20 kΩ 40 kΩ
+ 2.5 V
CDAC
(0.3125 V to 2.8125 V)
ADS8507
SLAS381 – DECEMBER 2006
Figure 44. Typical Transfer Functions With and Without External Resistors
To further analyze the effects of removing any combination of the external resistors, consider Figure 45 . The
combination of the external and the internal resistors form a voltage divider which reduces the input signal to a
0.3125-V to 2.8125-V input range at the capacitor digital-to-analog converter (CDAC). The internal resistors are
laser trimmed to high relative accuracy to meet full-scale specifications. The actual input impedance of the
internal resistor network looking into pin 1 or pin 3 however, is only accurate to ±20% due to process variations.
This should be taken into account when determining the effects of removing the external resistors.
Figure 45. Circuit Diagrams Showing External and Internal Resistors
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