Datasheet

AD7980 Data Sheet
Rev. C | Page 14 of 28
Transfer Functions
The ideal transfer characteristic for the AD7980 is shown in
Figure 26 and Table 7.
000 ... 000
000 ... 001
000 ... 010
111 ... 101
111 ... 110
111 ... 111
–FSR
–FSR + 1LSB
–FSR + 0.5LSB
+FSR – 1 LSB
+FSR – 1.5 LSB
06392-012
ANALOG INPUT
ADC CODE (STRAIGHT BINARY)
Figure 26. ADC Ideal Transfer Function
Table 7. Output Codes and Ideal Input Voltages
Analog Input
Description V
REF
= 5 V Digital Output Code (Hexa)
FSR – 1 LSB 4.999924 V FFFF
1
Midscale + 1 LSB 2.500076 V 8001
Midscale 2.5 V 8000
Midscale – 1 LSB 2.499924 V 7FFF
–FSR + 1 LSB 76.3 µV 0001
–FSR 0 V 0000
2
1
This is also the code for an overranged analog input (V
IN+
− V
IN−
above V
REF
− V
GND
).
2
This is also the code for an underranged analog input (V
IN+
− V
IN−
below V
GND
).
TYPICAL CONNECTION DIAGRAM
Figure 27 shows an example of the recommended connection
diagram for the AD7980 when multiple supplies are available.
06392-013
AD7980
3- OR 4-WIRE INTERFACE
2.5VV+
20Ω
V+
V–
0 TO VREF
1.8V TO 5V
100nF
10µF
2
2.7nF
4
100nF
REF
IN+
IN–
VDD VIO
SDI
CNV
SCK
SDO
GND
REF
1
1
SEE THE VOLTAGE REFERENCE INPUT SECTION FOR REFERENCE SELECTION.
2
C
REF
IS USUALLY A 10µF CERAMIC CAPACITOR (X5R).
3
SEE THE DRIVER AMPLIFIER CHOICE SECTION.
4
OPTIONAL FILTER. SEE THE ANALOG INPUT SECTION.
5
SEE THE DIGITAL INTERFACE FOR THE MOST CONVENIENT INTERFACE MODE.
Figure 27. Typical Application Diagram with Multiple Supplies