Datasheet

AD7292 Data Sheet
Rev. 0 | Page 16 of 40
ADC TRANSFER FUNCTIONS
The output coding of the AD7292 is 10-bit straight binary for the
analog input channels. The designated code transitions occur at
successive LSB values.
To select the input range, set the appropriate bits in the VIN
RANGE1 and VIN RANGE0 subregisters of the configuration
register bank (see Table 10).
The LSB size depends on the input range selected (see Table 9).
Table 9. Input Range and LSB Size
Input Range LSB Size
0 V to V
REF
V
REF
/2
10
0 V to 2 × V
REF
2V
REF
/2
10
0 V to 4 × V
REF
4V
REF
/2
10
The ideal transfer function for the AD7292 when operating
with an input range of 0 V to V
REF
is shown in Figure 34.
Table 10. Analog Input Range Selection
Sample with Respect to A
GND
Sample with Respect to AV
DD
2
Subregister Bit Settings
1
Single-Ended Input Range Differential Input Range Single-Ended Input Range
VIN RANGE1 VIN RANGE0 (VIN0 to VIN7) (VIN0 and VIN1 Only) (VIN0 to VIN7)
0 0 0 V to 4 × V
REF
−4 × V
REF
to +4 × V
REF
(AV
DD
− 4 × V
REF
) to AV
DD
0 1 0 V to 2 × V
REF
−2 × V
REF
to +2 × V
REF
Not applicable
1 0 0 V to 2 × V
REF
−2 × V
REF
to +2 × V
REF
Not applicable
1 1 0 V to V
REF
−V
REF
to +V
REF
Not applicable
1
For more information, see the ADC Sampling Mode Subregister (Address 0x12) section.
2
The contents of the VIN RANGE0 and VIN RANGE1 subregisters are ignored when the AD7292 is configured to sample with respect to AV
DD
; the only input range
allowed when sampling with respect to AV
DD
is from (AV
DD
− 4 × V
REF
) to AV
DD
.
111...111
111...110
111...000
011...111
000...010
000...001
000...000
1LSB = V
REF
/1024
ANALOG INPUT
NOTES
1. V
REF
IS 1.25V.
2. INPUT RANGE IS 0V TO V
REF
.
ADC CODE
+V
REF
– 1LSB1LSB
0V
10660-040
Figure 34. Straight Binary Transfer Characteristic Corresponding to Single-Ended Input Range of 0 V to V
REF
Table 11. Output Codes and Ideal Input Voltages (AV
DD
= 5 V)
Description
Analog Input Range
Digital Output
Code (Hex)
Single-Ended Mode of Operation Differential Mode of Operation
0 V to
4 × V
REF
0 V to
2 × V
REF
0 V to V
REF
(AV
DD
− 4 × V
REF
)
to AV
DD
−4 × V
REF
to
+4 × V
REF
−2 × V
REF
to
+2 × V
REF
−V
REF
to +V
REF
+FSR − 1 LSB 4.995117 V 2.497559 V 1.248779 V 4.995117 V 4.990234 V 2.495117 V 1.247559 V 0x3FF
Midscale + 1 LSB 2.504883 V 1.252441 V 0.626221 V 2.504883 V 0.009766 V 0.004883 V 0.002441 V 0x201
Midscale 2.5 V 1.25 V 0.625 V 2.5 V 0 V 0 V 0 V 0x200
Midscale − 1 LSB 2.495117 V 1.247559 V 0.623779 V 2.495117 V −0.009766 V −0.004883 V −0.002441 V 0x1FF
−FSR + 1 LSB 0.004883 V 0.002441 V 0.001221 V 0.004883 V 4.995117 V −2.495117 V −1.247559 V 0x001
−FSR 0 V 0 V 0 V 0 V −5 V −2.5 V −1.25 V 0x000