Datasheet

Data Sheet AD7949
Rev. D | Page 15 of 32
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 AD7949 is shown in
Figure 24 and for both unipolar and bipolar ranges with the
internal 4.096 V reference.
100...000
100...001
100...010
011...101
011...110
011...111
TWOS
COMPLEMENT
STRAIGHT
BINARY
000...000
000...001
000...010
111...101
111...110
111...111
ADC CODE
ANALOG INPUT
+FSR – 1.5LSB
+FSR – 1LSB
–FSR + 1LSB
–FSR
–FSR + 0.5LSB
07351-024
Figure 24. ADC Ideal Transfer Function
Table 7. Output Codes and Ideal Input Voltages
Description
Unipolar Analog Input
1
V
REF
= 4.096 V
Digital Output Code
(Straight Binary Hex)
Bipolar Analog Input
2
V
REF
= 4.096 V
Digital Output Code
(Twos Complement Hex)
FSR − 1 LSB 4.095750 V 0x3FFF
3
2.047750 V 0x1FFF
3
Midscale + 1 LSB 2.048250 V 0x2001 250 μV 0x0001
Midscale 2.048000 V 0x2000 0 V 0x0000
Midscale − 1 LSB 2.047750 V 0x1FFF −250 μV 0x3FFF
−FSR + 1 LSB 250 μV 0x0001 −2.047750 V 0x2001
−FSR 0 V 0x0000
4
−2.048 V 0x2000
4
1
With COM or INx− = 0 V or all INx referenced to GND.
2
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
− GND).
4
This is also the code for an underranged analog input ((INx+) − (INx−), or COM, below GND).