AD7682/AD7689
TRANSFER FUNCTIONS
With the inputs configured for unipolar range (single ended,
COM with ground sense, or paired differentially with INx− as
ground sense), the data output is straight binary.
With the inputs configured for bipolar range (COM = V
REF
/2 or
paired differentially with INx− = V
REF
/2), the data outputs are
twos complement.
The ideal transfer characteristic for the AD7682/AD7689 is
shown in Figure 25 and for both unipolar and bipolar ranges
with the internal 4.096 V reference.
TWOS
STRAIGHT
COMPLEMENT
BINARY
011...111
011...110
011...101
111...111
111...110
111...101
ADC CODE
100...010
100...001
100...000
000...010
000...001
000...000
–FSR
–FSR + 1LSB
+FSR – 1LSB
+FSR – 1.5LSB
ANALOG INPUT
–FSR + 0.5LSB
Figure 25. ADC Ideal Transfer Function
Table 7. Output Codes and Ideal Input Voltages
Description
FSR − 1 LSB
Midscale + 1 LSB
Midscale
Midscale − 1 LSB
−FSR + 1 LSB
−FSR
1
2
Unipolar Analog Input
V
REF
= 4.096 V
4.095938 V
2.048063 V
2.048 V
2.047938 V
62.5 μV
0V
Digital Output Code
(Straight Binary Hex)
0xFFFF
0x8001
0x8000
0x7FFF
0x0001
0x0000
Bipolar Analog Input
V
REF
= 4.096 V
2.047938 V
62.5 μV
0V
−62.5 μV
−2.047938 V
−2.048 V
Digital Output Code
(Twos Complement Hex)
0x7FFF
0x0001
0x0000
0xFFFF
0x8001
0x8000
With COM or INx− = 0 V or all INx referenced to GND.
With COM or INx− = V
REF
/2.
3
This is also the code for an overranged analog input ((INx+) − (INx−), or COM, above V
REF
− V
GND
).
4
This is also the code for an underranged analog input ((INx+) − (INx−), or COM, below V
GND
).
Rev. 0 | Page 16 of 28
07353-027
AD [ ANALOG DEVICES ]
