AD7693 데이터 시트보기 (PDF) - Analog Devices
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AD7693 Datasheet PDF : 24 Pages
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Preliminary Technical Data
AD7693
SINGLE-TO-DIFFERENTIAL DRIVER
For applications using a single-ended analog signal, either
bipolar or unipolar, the ADA4941-1 single-ended-to-differential
driver allows for a differential input into the part. The
schematic is shown in Figure 29.
R1 and R2 set the attenuation ratio between the input range and
the ADC range (VREF). R1, R2, and CF will be chosen depending
on the desired input resistance, signal bandwidth, antialiasing
and noise contribution. For example, for the ±10 V range with a
4 kΩ impedance, R2 = 1 kΩ and R1 = 4 kΩ.
R3 and R4 set the common mode on the IN− input, and R5 and
R6 set the common mode on the IN+ input of the ADC. The
common mode should be set close to VREF/2; however, if single
supply is desired, it can be set slightly above VREF/2 to provide
some headroom for the ADA4941-1 output stage. For example,
for the ±10 V range with a single supply, R3 = 8.45 kΩ, R4 =
11.8 kΩ, R5 = 10.5 kΩ, and R6 = 9.76 kΩ.
R5
R6
R3
100nF
100nF
R4
+5.2V
10µF
+5V REF
+5.2V
15Ω
15Ω
2.7nF
2.7nF
ADA4941
REF VDD
IN+
AD7693
IN–
GND
±10V, ±5V, ...
R1
R2
CF
Figure 29. Single-Ended-to-Differential Driver Circuit
VOLTAGE REFERENCE INPUT
The AD7693 voltage reference input, REF, has a dynamic input
impedance and should therefore be driven by a low impedance
source with efficient decoupling between the REF and GND
pins, as explained in the Layout section.
When REF is driven by a very low impedance source, for
example, a reference buffer using the AD8031 or the AD8605, a
10 μF (X5R, 0805 size) ceramic chip capacitor is appropriate for
optimum performance.
If an unbuffered reference voltage is used, the decoupling value
depends on the reference used. For instance, a 22 μF (X5R,
1206 size) ceramic chip capacitor is appropriate for optimum
performance using low temperature drift ADR43x and ADR44x
references.
If desired, smaller reference decoupling capacitor values down
to 2.2 μF can be used with a minimal impact on performance,
especially DNL.
Regardless, there is no need for an additional lower value
ceramic decoupling capacitor (for example, 100 nF) between the
REF and GND pins.
POWER SUPPLY
The AD7693 uses two power supply pins: a core supply, VDD,
and a digital input/output interface supply, VIO. VIO allows
direct interface with any logic between 1.8 V and VDD. To
reduce the supplies needed, the VIO and VDD pins can be tied
together. The AD7693 is independent of power supply sequencing
between VIO and VDD. Additionally, it is very insensitive to
power supply variations over a wide frequency range, as shown
in Figure 30.
90
VREF = VDD = 5V
85
80
75
70
65
60
55
50
45
40
1
10
100
1000
10000
FREQUENCY (kHz)
Figure 30. PSRR vs. Frequency
The AD7693 powers down automatically at the end of each
conversion phase and, therefore, the power scales linearly with
the sampling rate. This makes the part ideal for low sampling
rate (even a few hertz) and low battery-powered applications.
10000
1000
100
VDD = 5V
10
VIO
1
0.1
0.01
0.001
10
100
1k
10k
100k
1M
SAMPLING RATE (SPS)
Figure 31. Operating Currents vs. Sample Rate
Rev. PrB | Page 15 of 24
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