Datasheet
AD7265
Rev. A | Page 18 of 28
TRANSFER FUNCTIONS DIGITAL INPUTS
The designed code transitions occur at successive integer LSB
values (1 LSB, 2 LSB, and so on). In single-ended mode, the LSB
size is V
The digital inputs applied to the AD7265 are not limited by the
maximum ratings that limit the analog inputs. Instead, the
digital inputs can be applied up to 7 V and are not restricted by
the V
/4096 when the 0 V to V
REF REF
range is used, and the LSB
size is 2 × V
/4096 when the 0 V to 2 × V
REF REF
range is used. In
differential mode, the LSB size is 2 × V
+ 0.3 V limit, as are the analog inputs. See the
DD
Absolute
Maximum Ratings
REF
/4096 when the 0 V to
V
section for more information. Another
advantage of the SCLK, RANGE, A0 to A2, and
REF
range is used, and the LSB size is 4 × V
REF
/4096 when the
0 V to 2 × V
CS
pins not
being restricted by the V
REF
range is used. The ideal transfer characteristic
for the AD7265 when straight binary coding is output is shown
in
DD
+ 0.3 V limit is that power supply
sequencing issues are avoided. If one of these digital inputs is
applied before V
Figure 32, and the ideal transfer characteristic for the AD7265
when twos complement coding is output is shown (with the 2 ×
V
DD
, there is no risk of latch-up, as there would
be on the analog inputs if a signal greater than 0.3 V were
applied prior to V
range) in Figure 33.
REF
DD
.
04674-027
000...000
111...111
1LSB = V
REF
/4096
1LSB
V
REF
– 1LSB
ANALOG INPUT
ADC CODE
0V
000...001
000...010
111...110
111...000
011...111
NOTE
1. V
REF
IS EITHER V
REF
OR 2 × V
REF
.
V
DRIVE
The AD7265 also has a V
DRIVE
feature to control the voltage at
which the serial interface operates. V
DRIVE
allows the ADC to
easily interface to both 3 V and 5 V processors. For example, if
the AD7265 was operated with a V
of 5 V, the V
DD DRIVE
pin
could be powered from a 3 V supply, allowing a large dynamic
range with low voltage digital processors. Therefore, the
AD7265 could be used with the 2 × V
input range, with a V
REF DD
of 5 V while still being able to interface to 3 V digital parts.
Figure 32. Straight Binary Transfer Characteristic
04674-028
100...000
011...111
1LSB = 2
×
V
REF
/4096
+V
REF
– 1 LSB–V
REF
+ 1LSB V
REF
– 1LSB
ANALOG INPUT
ADC CODE
100...001
100...010
011...110
000...001
000...000
111...111
Figure 33. Twos Complement Transfer Characteristic with
V
± V Input Range
REF REF