Datasheet

AD7685
Rev. C | Page 14 of 28
Transfer Functions
The ideal transfer characteristic for the AD7685 is shown in
Figure 26 and Table 8.
000...000
000...001
000...010
111...101
111...110
111...111
ADC CODE (STRAIGHT BIN
A
R
Y)
ANALOG INPUT
+FS – 1.5 LSB
+FS – 1 LSB
–FS + 1 LSB
–FS
–FS + 0.5 LSB
02968-024
Figure 26. ADC Ideal Transfer Function
TYPICAL CONNECTION DIAGRAM
Figure 27 shows an example of the recommended connection
diagram for the AD7685 when multiple supplies are available.
AD7685
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
02968-025
NOTES
1. SEE 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 FOR MOST CONVENIENT INTERFACE MODE.
Figure 27. Typical Application Diagram with Multiple Supplies
Table 8. Output Codes and Ideal Input Voltages
Description Analog Input 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
).