AD7450ABRT-R2 Analog Devices Inc, AD7450ABRT-R2 Datasheet - Page 17

IC ADC 12BIT W/DIFF INP SOT-23-8

AD7450ABRT-R2

Manufacturer Part Number
AD7450ABRT-R2
Description
IC ADC 12BIT W/DIFF INP SOT-23-8
Manufacturer
Analog Devices Inc
Datasheet

Specifications of AD7450ABRT-R2

Rohs Status
RoHS non-compliant
Number Of Bits
12
Sampling Rate (per Second)
1M
Data Interface
DSP, MICROWIRE™, QSPI™, Serial, SPI™
Number Of Converters
1
Power Dissipation (max)
9.25mW
Voltage Supply Source
Single Supply
Operating Temperature
-40°C ~ 85°C
Mounting Type
Surface Mount
Package / Case
SOT-23-8
For Use With
EVAL-AD7450CBZ - BOARD EVALUATION FOR AD7450
Other names
AD7450ABRT-R2
AD7450ABRT-R2TR
Figure 30 shows examples of the inputs to V
different values of V
and minimum common-mode voltages for each reference value
according to Figure 28.
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.
Conversion Phase–Switches Open; Track Phase–Switches Closed
Figure 30. Examples of the Analog Inputs to V
V
V
COMMON-MODE (CM)
COMMON-MODE (CM)
IN+
IN–
Figure 31. Equivalent Analog Input Circuit
Different Values of V
CM
CM
REF
C1
C1
CM
MAX
CM
MIN
MAX
for V
MIN
= 1.25V
= 3.75V
REFERENCE = 2.5V
REFERENCE = 2V
= 1V
= 4V
D
D
D
D
DD
V
V
DD
DD
= 5 V. It also gives the maximum
REF
for V
V
V
V
V
IN–
IN+
IN–
IN+
DD
R1
R1
2V p-p
2.5V p-p
= 5 V
IN+
IN+
C2
C2
and V
and V
IN–
IN–
for
for
Rev. C | Page 17 of 28
For ac applications, removing high frequency components from
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
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
distortion (THD) that can be tolerated. The THD increases as
the source impedance increases, and performance degrades.
Figure 32 shows a graph of THD vs. the analog input signal
frequency for different source impedances for V
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
source impedance is 10 Ω.
Figure 32. THD vs. Analog Input Frequency for Various Source Impedances
Figure 33. THD vs. Analog Input Frequency for 3 V and 5 V Supply Voltages
–100
–20
–40
–60
–80
–50
–55
–60
–65
–70
–75
–80
–85
–90
0
10
10
T
V
A
T
DD
A
= 25 ° C
= 25 ° C
= 5V
DD
of 5 V ± 5% and 3 V + 20%/–10%, while
INPUT FREQUENCY (kHz)
INPUT FREQUENCY (kHz)
for V
R
IN
DD
R
IN
= 10
100
100
= 5 V
= 510
Ω
AD7440/AD7450A
V
Ω
V
DD
DD
R
= 3.6V
= 4.75V
IN
= 1k
V
DD
R
Ω
IN
V
DD
= 2.7V
DD
= 300
= 5 V.
= 5.25V
Ω
1000
1000

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