EVAL-CONTROLBRD2 AD [Analog Devices], EVAL-CONTROLBRD2 Datasheet - Page 16

• Manufacturer Part Number: EVAL-CONTROLBRD2
• Description: Differential Input, 1MSPS, 12-Bit ADC in ?SO-8 and S0-8
• Manufacturer: AD [Analog Devices]

REFERENCE SECTION
An external reference source is required to supply the
reference to the AD7450.
from 100 mV to 2.5 V. With a 5V power supply, the
specified and maximum reference is 2.5V. With a 3V
power supply, the specified reference is 1.25V and the
maximum reference is 2.2V. In both cases, the reference is
functional from 100mV. It is important to note that as the
reference input moves closer to the maximum reference
input, the performance improves.
device from V
input range (VINmax) must never be greater than V
0.3V to comply with the maximum ratings of the device.
For example:
Therefore, when operating at V
V
When V
When operating from V
no need to worry about the maximum analog input in
relation to V
the maximum analog input span being 3.75 V which is not
close to V
The performance of the part at different reference values is
shown in TPC9 to TPC13 and in TPC16 and TPC17.
The value of the reference sets the analog input span and
the common mode voltage range. Errors in the reference
source will result in gain errors in the AD7450 transfer
function and will add to specified full scale errors on the
part. A capacitor of 0.1µF should be used to decouple the
V
age references that could be used that are available from
Analog Devices and Figure 17 shows a typical connection
diagram for the V
AD7450
REF
REF
VINmax = V
VINmax = V
If V
then VINmax = 3.6 V
Therefore 3xV
V
REF
Figure 16. Using an RF Transformer to Generate
can range from 100mV to a maximum value of 2.4V.
pin to GND. Table I lists examples of suitable volt-
DD
max = 2.4 V
R
DD
= 3.3V
DD
= 2.7 V, V
DD
.
DD
REF
DD
REF
as the maximum V
= 2.7V to 3.3V, the maximum analog
/2 = 3.6 V
REF
+ 0.3
+ V
Differential Inputs
pin.
REF
R
R
DD
REF
/2
max = 2 V.
= 4.75 V to 5.25 V, there is
This reference input can range
PRELIMINARY TECHNICAL DATA
C
DD
2.5V
1.25V
3.75V
= 3.3 V, the value of
3.75V
1.25V
V IN-
2.5V
When operating the
REF
V IN+
EXTERNAL
V REF (2.5V)
AD7450
is 2.5 V resulting
V REF
DD
+
–16–
Reference Output
AD589
AD1580
REF192
REF43
AD780
VDD
SINGLE ENDED OPERATION
When supplied with a 5 V power supply, the AD7450 can
handle a single ended input. The design of this part is
optimized for differential operation so with a single ended
input performance will degrade. Linearity will degrade by
typically 0.2LSBs, Zero Code and the Full Scale Errors
will degrade by typically 2LSBs and AC performance is
not guaranteed.
To operate the AD7450 in single ended mode, the V
input is coupled to the signal source while the V
biased to the appropriate voltage corresponding to the
mid-scale code transition.
Mode, which is a fixed dc voltage (usually the reference).
The V
voltage span of 2 x V
range of the part. The input signal will therefore have peak
to peak values of Common Mode ±V
input is unipolar then an opamp in a non-inverting
unity gain configuration can be used to drive the V
Because the ADC operates from a single supply, it will be
necessary to level shift ground based bipolar signals to
comply with the input requirements.
configured to rescale and level shift the ground based bi-
polar signal so it is compatible with the selected input
range of the AD7450 (see Figure 18).
*ADDITIONAL PINS OMITTED FOR CLARITY
0.1µF
Table I Examples of Suitable Voltage References
IN+
Figure 17. Typical V
input swings around this value and should have
10nF
Voltage
1.235
1.225
2.5
2.5
2.5
0.1µF
NC
REF
1
2
3
4
to make use of the full dynamic
Temp
0.08-0.8
0.08-0.4
0.06-0.1
0.04-0.2
VIN
GND
(% max)
1.2-2.8
Initial
Accuracy
This voltage is the Common
AD780
REF
OpSel
Connection Diagram
Vout
Trim
8
7
5
6
REF
An opamp can be
NC
NC
NC
.
If the analog
Operating
Current
IN-
(µA)
1000
AD7450*
600
REV. PrJ
50
50
45
IN+
input is
V REF
V DD
IN+
pin.
0.1µF