Datasheet

AD7686
Rev. B | Page 13 of 28
Transfer Functions
The ideal transfer characteristic for the AD7686 is shown in
Figure 25 and Table 7.
000...000
000...001
000...010
111...101
111...110
111...111
ADC CODE (STRAIGHT BIN
A
R
Y)
ANALOG INPUT
+FSR – 1.5 LSB
+FSR – 1 LSB
–FSR + 1 LSB
–FSR
–FSR + 0.5 LSB
02969-025
Figure 25. ADC Ideal Transfer Function
Table 7. Output Codes and Ideal Input Voltages
Description
Analog Input
V
REF
= 5 V
Digital Output Code
Hexadecimal
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
TYPICAL CONNECTION DIAGRAM
Figure 26 shows an example of the recommended connection
diagram for the AD7686 when multiple supplies are available.
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 − V below V ).
IN+ IN− GND
AD7686
REF
GND
VDD
IN–
IN+
VIO
SDI
SCK
SDO
CNV
3- OR 4-WIRE INTERFACE
5
100nF
100nF
5V
10µF
2
≥7V
≥7V
≤–2V
1.8V TO VDD
REF
1
0 TO VREF
33Ω
2.7nF
3
4
02969-026
1
SEE THE VOLTAGE REFERENCE INPUT SECTION FOR REFERENCE SELECTION.
2
C
REF
IS USUALLY A 10µF CERAMIC CAPACITOR (X5R).
3
SEE DRIVER AMPLIFIER CHOICE SECTION.
4
OPTIONAL FILTER. SEE ANALOG INPUT SECTION.
5
SEE DIGITAL INTERFACE SECTION FOR MOST CONVENIENT INTERFACE MODE.
Figure 26. Typical Application Diagram with Multiple Supplies