Datasheet

AD7690
Rev. B | Page 13 of 24
Transfer Functions
The ideal transfer characteristic for the AD7690 is shown in
Figure 25 and Table 7.
100...000
100...001
100...010
011...101
011...110
011...111
ADC CODE (TWOS COMPLEMENT)
ANALOG INPUT
+FSR – 1.5LSB
+FSR – 1LSB
–FSR + 1LSB
–FSR
–FSR + 0.5LSB
05792-007
Figure 25. 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 26 shows an example of the recommended connection
diagram for the AD7690 when multiple supplies are available.
AD7690
REF
GND
VDD
IN–
IN+
VIO
SDI
SCK
SDO
CNV
3- OR 4-WIRE INTERFACE
5
100nF
100nF
5V
10µF
2
V+
V+
V–
1.8V TO VDD
REF
1
0 TO V
REF
15Ω
2.7nF
4
V+
V–
V
REF
TO 0
15Ω
2.7nF
ADA4841-2
3
ADA4841-2
3
4
1
SEE VOLTAGE REFERENCE INPUT SECTION FOR REFERENCE SELECTION.
2
C
REF
IS USUALLY A 10µF CERAMIC CAPACITOR (X5R).
3
SEE TABLE 8 FOR ADDITIONAL RECOMMENDED AMPLIFIERS.
4
OPTIONAL FILTER. SEE ANALOG INPUT SECTION.
5
SEE THE DIGITAL INTERFACE SECTION FOR MOST CONVENIENT INTERFACE MODE.
05792-008
Figure 26. Typical Application Diagram with Multiple Supplies