Datasheet

AD7631 Data Sheet
Rev. B | Page 18 of 32
TRANSFER FUNCTIONS
Using the D0/OB/
2C
digital input or via the configuration
register, except in 18-bit parallel interface mode, the AD7631
offers two output codings: straight binary and twos
complement. See Figure 26 and Table 8 for the ideal transfer
characteristic and digital output codes for the different analog
input ranges, V
IN
. Note that when using the configuration
register, the D0/OB/
2C
input is a don’t care and should be tied
to either high or low.
000...000
000...001
000...010
111...101
111...110
111...111
ADC CODE (Straight Binary)
ANALOG INPUT
+FSR – 1.5 LSB
+FSR –1LSB–FSR + 1 LSB
–FSR
–FSR + 0.5 LSB
06588-026
Figure 26. ADC Ideal Transfer Function
TYPICAL CONNECTION DIAGRAM
Figure 27 shows a typical connection diagram for the AD7631
using the internal reference, serial data interface, and serial
configuration port. Different circuitry from that shown in
Figure 27 is optional and is discussed in the following sections.
Table 8. Output Codes and Ideal Input Voltages
V
REF
= 5 V Digital Output Code
Description
V
IN
= 0 V to 5 V
(10 V p-p)
V
IN
= 0 V to 10 V
(20 V p-p)
V
IN
= ±5 V
(20 V p-p)
V
IN
= ±10 V
(40 V p-p)
Straight Binary Twos Complement
FSR − 1 LSB +4.999962 V +9.999924 V +9.999924 V +19.999847 V 0x3FFFF
1
0x1FFFF
1
FSR − 2 LSB +4.999924 V +9.999847 V +9.999847 V +19.999695 V 0x3FFFE 0x1FFFE
Midscale + 1 LSB +38.15 µV −76.29 µV −76.29 µV +152.59 µV 0x20001 0x00001
Midscale 0 V 0 V 0 V 0 V 0x20000 0x00000
Midscale − 1 LSB −38.15 µV −76.29 µV −76.29 µV −152.59 µV 0x1FFFF 0x3FFFF
−FSR + 1 LSB −4.999962 V −9.999924 V −9.999924 V −19.999847 V 0x00001 0x20001
−FSR −5 V −10 V −10 V −20 V 0x00000
2
0x20000
2
1
This is also the code for overrange analog input.
2
This is also the code for underrange analog input.