EVAL-AD7450ASDZ

Manufacturer Part NumberEVAL-AD7450ASDZ
DescriptionData Conversion IC Development Tools EVALUATION BOARD I.C.
ManufacturerAnalog Devices
TypeADC
SeriesAD7450A
EVAL-AD7450ASDZ datasheet
 

Specifications of EVAL-AD7450ASDZ

RohsyesProductEvaluation Boards
Tool Is For Evaluation OfAD7450AInterface TypeSerial
Operating Supply Voltage2.7 V to 5.25 VMaximum Operating Temperature+ 85 C
Minimum Operating Temperature- 40 CFactory Pack Quantity1
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AD7440/AD7450A
TYPICAL CONNECTION DIAGRAM
Figure 26 shows a typical connection diagram for the
AD7440/AD7450A for both 5 V and 3 V supplies. In this setup,
the GND pin is connected to the analog ground plane of the
system. The V
pin is connected to either a 2.5 V or a 2 V
REF
decoupled reference source, depending on the power supply, to
set up the analog input range. The common-mode voltage has
to be set up externally and is the value on which the two inputs
are centered. The conversion result is output in a 16-bit word
with four leading zeros followed by the MSB of the 12-bit or
10-bit result. The 10-bit result of the AD7440 is followed by two
trailing zeros. For more details on driving the differential inputs
and setting up the common mode, refer to the Driving
Differential Inputs section.
μ
μ
0.1
F
10
F
V
DD
V
REF
CM*
V
IN+
p-p
AD7440/
AD7450A
V
REF
CM*
V
IN–
p-p
V
REF
2V/2.5V
V
REF
μ
0.1
F
*CM IS THE COMMON-MODE VOLTAGE.
Figure 26. Typical Connection Diagram
ANALOG INPUT
The analog input of the AD7440/AD7450A is fully differential.
Differential signals have a number of benefits over single-
ended signals, including noise immunity based on the device’s
common-mode rejection, improvements in distortion perfor-
mance, doubling of the device’s available dynamic range, and
flexibility in input ranges and bias points. Figure 27 defines the
fully differential analog input of the AD7440/AD7450A.
V
REF
p-p
V
REF
p-p
COMMON-MODE
VOLTAGE
Figure 27. Differential Input Definitions
The amplitude of the differential signal is the difference
between the signals applied to the V
IN+
(i.e., V
– V
). V
and V
are simultaneously driven by
IN+
IN–
IN+
IN–
two signals each of amplitude V
that are 180° out of phase.
REF
The amplitude of the differential signal is therefore –V
+V
peak-to-peak (2 × V
). This is true regardless of the
REF
REF
common mode (CM).
The common mode is the average of the two signals, that is,
(V
IN+
are centered on. This results in the span of each input being
CM ± V
range varies with V
common-mode range decreases. When driving the inputs with
an amplifier, the actual common-mode range is determined by
the amplifier’s output voltage swing.
Figure 28 and Figure 29 show how the common-mode range
typically varies with V
The common mode must be in this range to guarantee the
functionality of the AD7440/AD7450A.
For ease of use, the common mode can be set up to equal V
resulting in the differential signal being ±V
3V/5V
SUPPLY
When a conversion takes place, the common mode is rejected,
SERIAL
resulting in a virtually noise-free signal of amplitude –V
INTERFACE
+V
REF
case of the AD7450A and 0 to 1024 in the AD7440.
SCLK
μ
μ
SDATA
C/
P
CS
GND
V
IN+
AD7440/
AD7450A
V
IN–
and V
pins
IN–
to
REF
Rev. C | Page 16 of 28
+ V
)/2 and is therefore the voltage that the two inputs
IN–
/2. This voltage has to be set up externally, and its
REF
. As the value of V
increases, the
REF
REF
for both a 5 V and a 3 V power supply.
REF
REF
, corresponding to the digital codes of 0 to 4096 in the
4.5
4.0
3.5
3.0
2.5
COMMON-MODE RANGE
2.0
1.5
1.0
0.5
0
0
0.5
1.0
1.5
2.0
2.5
V
(V)
REF
Figure 28. Input Common-Mode Range vs. V
(V
= 5 V and V
(Max) = 3.5 V)
DD
REF
2.5
2.0
1.5
COMMON-MODE RANGE
1.0
0.5
0
0
0.25
0.50
0.75
1.00
1.25
1.50
V
(V)
REF
Figure 29. Input Common-Mode Range vs. V
(V
= 3 V and V
(Max) =2V)
DD
REF
,
REF
centered on V
.
REF
to
REF
3.25V
1.75V
3.0
3.5
REF
2V
1V
1.75
2.00
REF