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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Figure 30 shows examples of the inputs to V
different values of V
for V
= 5 V. It also gives the maximum
REF
DD
and minimum common-mode voltages for each reference value
according to Figure 28.
REFERENCE = 2V
V
IN–
COMMON-MODE (CM)
CM
= 1V
MIN
CM
= 4V
MAX
V
IN+
REFERENCE = 2.5V
V
IN–
COMMON-MODE (CM)
CM
= 1.25V
MIN
CM
= 3.75V
MAX
V
IN+
Figure 30. Examples of the Analog Inputs to V
Different Values of V
for V
REF
Analog Input Structure
Figure 31 shows the equivalent circuit of the analog input
structure of the AD7440/AD7450A. The four diodes provide
ESD protection for the analog inputs. Care must be taken to
ensure that the analog input signals never exceed the supply
rails by more than 300 mV. This causes these diodes to become
forward biased and start conducting into the substrate. These
diodes can conduct up to 10 mA without causing irreversible
damage to the part. The capacitors, C1 in Figure 31, are
typically 4 pF and can primarily be attributed to pin
capacitance. The resistors are lumped components made up of
the on resistance of the switches. The value of these resistors is
typically about 100 Ω. The capacitors, C2, are the ADC’s
sampling capacitors and have a capacitance of 16 pF typically.
V
DD
D
V
IN+
D
C1
V
DD
D
V
IN–
C1
D
Figure 31. Equivalent Analog Input Circuit
Conversion Phase–Switches Open; Track Phase–Switches Closed
and V
for
For ac applications, removing high frequency components from
IN+
IN–
the analog input signal through the use of an RC low-pass filter
on the relevant analog input pins is recommended. In applica-
tions where harmonic distortion and signal-to-noise ratio are
critical, the analog input should be driven from a low impe-
dance source. Large source impedances significantly affect the
ac performance of the ADC. This may necessitate the use of an
input buffer amplifier. The choice of op amp is a function of the
2V p-p
particular application.
When no amplifier is used to drive the analog input, the source
impedance should be limited to low values. The maximum
source impedance depends on the amount of total harmonic
2.5V p-p
distortion (THD) that can be tolerated. The THD increases as
the source impedance increases, and performance degrades.
and V
for
IN+
IN–
= 5 V
Figure 32 shows a graph of THD vs. the analog input signal
DD
frequency for different source impedances for V
Figure 32. THD vs. Analog Input Frequency for Various Source Impedances
Figure 33 shows a graph of the THD vs. the analog input
frequency for V
sampling at 1 MSPS with an SCLK of 18 MHz. In this case, the
C2
R1
source impedance is 10 Ω.
C2
R1
Figure 33. THD vs. Analog Input Frequency for 3 V and 5 V Supply Voltages
Rev. C | Page 17 of 28
AD7440/AD7450A
0
= 25 ° C
T
A
V
= 5V
DD
–20
–40
R
= 1k
IN
Ω
R
= 510
IN
–60
–80
Ω
R
= 10
IN
–100
10
100
INPUT FREQUENCY (kHz)
for V
= 5 V
DD
of 5 V ± 5% and 3 V + 20%/–10%, while
DD
–50
= 25 ° C
T
A
–55
V
–60
–65
V
= 3.6V
DD
–70
–75
–80
–85
V
= 4.75V
DD
–90
10
100
INPUT FREQUENCY (kHz)
= 5 V.
DD
Ω
Ω
R
= 300
IN
1000
= 2.7V
DD
V
= 5.25V
DD
1000