Datasheet

AD9480
Rev. A | Page 17 of 28
The AD9480 can be easily configured for different full-scale
ranges. See the Voltage Reference section for more information.
Optimal performance is achieved with a 1 V p-p analog input.
04619-013
SENSE = GND
VIN+
2.0V500mV 2.0V
VIN–
DIGITALOUT = ALL 1s DIGITALOUT = ALL 0s
Figure 33. Analog Input Full Scale
VOLTAGE REFERENCE
A stable and accurate 1.0 V reference is built into the AD9480.
Users can choose this internal reference or provide an external
reference for greater accuracy and flexibility. Figure 35 shows
the typical reference variation with temperature. Table 9
summarizes the available reference configurations.
SELECT
LOGIC
ADC
CORE
0.5V
7kΩ
VREF
0.1µF10µF
+
SENSE
VIN+
VIN–
04619-014
7kΩ
Figure 34. Internal Reference Equivalent Circuit
Fixed Reference
The internal reference can be configured for a differential span
of 1 V p-p (see Figure 37). It is recommended to place a 0.1 µF
capacitor as close as possible to the VREF pin; a 10 µF capacitor
is also required (see the PCB layout for guidance). If the
internal reference of the AD9480 is used to drive multiple
converters to improve gain matching, the loading of the
reference by the other converters must be considered. Figure 37
depicts how the internal reference voltage is affected by loading.
TEMPERATURE (°C)
VREF (V)
1.0085
1.0080
1.0075
1.0060
1.0055
1.0065
1.0070
1.0050
1.0045
1.0040
1.0035
–40 –20 0 20 40 60 80
04619-049
Figure 35. Typical Reference Variation with Temperature
04619-016
0.1µF10µF
VREF
SENSE
Figure 36. Internal Fixed Reference (1 V p-p)
IREF (mA)
% CHANGE IN VREF VOLTAGE
0
–0.1
–0.2
–0.4
–0.3
–0.5
0 0.5 1.51.0 2.0 2.5 3.0
04619-017
Figure 37. Internal VREF vs. Load Current
Table 9. Reference Configurations
SENSE Voltage Resulting VREF Reference Differential Span
AVDD N/A (External Reference Input) External 1 × External Reference Voltage
0.5 V (Self-Biased) 0.5 × (1 + R1/R2) V Programmable 1 × VREF (0.75 V p-p to 1.5 V p-p)
AGND to 0.2 V 1.0 V Internal Fixed 1 V p-p