Datasheet

AD7986
Rev. B | Page 14 of 28
Transfer Functions
The ideal transfer characteristic for the AD7986 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
07956-012
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 +4.095969 V 0x1FFFF
1
Midscale + 1 LSB +31.25 µV 0x00001
Midscale 0 V 0x00000
Midscale − 1 LSB −31.25 µV 0x3FFFF
−FSR + 1 LSB −4.095969 V 0x20001
−FSR −4.096 V 0x20000
2
1
This is also the code for an overranged analog input (V
IN+
− V
IN−
above V
REF
−
REFGND).
2
This is also the code for an underranged analog input (V
IN+
− V
IN−
below REFGND).
TYPICAL CONNECTION DIAGRAM
Figure 23 shows an example of the recommended connection
diagram for the AD7986 when multiple supplies are available.
2.7nF
15Ω
V–
0V TO V
REF
V+
2.7nF
15Ω
V–
V+
IN–
AD7986
IN+
REF
AVDD,
DVDD
DD
VIO
BVDD
5V
2.5V
1.8V TO 2.7V
VIO
SDI
SCLK
SDO
CNV
TURBO
10µF
V
REF
TO 0V
GND
1
07956-016
NOTES
1. GND REFERS TO REFGND, AGND, AND DGND.
3- OR 4-WIRE
INTERFACE:
SPI, CS
DAISY CHAIN (TURBO = LOW)
Figure 23. Typical Application Diagram with Multiple Supplies