Datasheet

Data Sheet AD7988-1/AD7988-5
Rev. D | Page 15 of 24
Transfer Functions
The ideal transfer characteristic for the AD7988-x is shown in
Figure 30 and Table 7.
000 ... 000
000 ... 001
000 ... 010
111 ... 101
111 ...
110
111 ...
11
1
–FSR
–FSR + 1LSB
–FSR + 0.5LSB
+FSR – 1 LSB
+FSR – 1.5 LSB
ANALOG INPUT
ADC CODE (STRAIGHT BINARY)
10231-031
Figure 30. ADC Ideal Transfer Function
Table 7. Output Codes and Ideal Input Voltages
Analog Input
Description V
REF
= 5 V Digital Output Code (Hex)
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
).
TYPICAL CONNECTION DIAGRAM
Figure 31 shows an example of the recommended connection
diagram for the AD7988-x when multiple supplies are available.
AD7988-1/
AD7988-5
2.5VV+
20Ω
V+
V–
0V TO V
REF
1.8V TO 5.5V
100nF
10µF
2
2.7nF
4
3
100nF
REF
IN+
IN–
VDD VIO
GND
3- OR 4-WIRE INTERFACE
5
REF
1
1
SEE THE VOLTAGE REFERENCE INPUT SECTION FOR REFERENCE SELECTION.
2
C
REF
IS USUALLY A 10µF CERAMIC CAPACITOR (X5R).
3
SEE THE DRIVER AMPLIFIER CHOICE SECTION.
4
OPTIONAL FILTER. SEE THE ANALOG INPUTS SECTION.
5
SEE THE DIGITAL INTERFACE SECTION FOR THE MOST CONVENIENT INTERFACE MODE.
10231-032
CNV
SCK
SDO
SDI
Figure 31. Typical Application Diagram with Multiple Supplies