Datasheet

AD7984
Rev. A | Page 13 of 24
Transfer Functions
The ideal transfer characteristic for the AD7984 is shown in
Figure 22 and Table 7.
100 ... 000
100 ... 001
100 ... 010
011 ... 101
011 ... 110
011 ... 111
ADC CODE (TWOS COMPLEMENT)
ANALOG INPUT
+FSR – 1.5 LSB
+FSR – 1 LSB
–FSR + 1 LSB
–FSR
–FSR + 0.5 LSB
0
6973-012
Figure 22. ADC Ideal Transfer Function
Table 7. Output Codes and Ideal Input Voltages
Description
Analog Input
V
REF
= 5 V
Digital Output
Code (Hex)
FSR − 1 LSB +4.999962 V 0x1FFFF
1
Midscale + 1 LSB +38.15 μV 0x00001
Midscale 0 V 0x00000
Midscale − 1 LSB −38.15 μV 0x3FFFF
−FSR + 1 LSB −4.999962 V 0x20001
−FSR −5 V 0x20000
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 23 shows an example of the recommended connection
diagram for the AD7984 when multiple supplies are available.
2.7nF
15Ω
V–
0 TO VREF
V+
4
2.7nF
15Ω
V–
V
REF TO 0
V+
4
10µF
2
REF
1
REF VDD VIO
GND
IN+
IN–
SDI
SCK
SDO
CNV
AD7984
100nF
100nF
3-WIRE INTERFACE
2.5V
1.8V TO 5V
V+
ADA4841
2, 3
NOTES
1
SEE VOLTAGE REFERENCE INPUT SECTION FOR REFERENCE SELECTION.
2
C
REF
IS USUALLY A 10µF CERAMIC CAPACITOR (X5R).
SEE RECOMMENDED LAYOUT IN FIGURE 40 AND FIGURE 41.
3
SEE DRIVER AMPLIFIER CHOICE SECTION.
4
OPTIONAL FILTER. SEE ANALOG INPUTS SECTION.
06973-013
Figure 23. Typical Application Diagram with Multiple Supplies