AD7693 Analog Devices, AD7693 Datasheet - Page 15

• Manufacturer Part Number: AD7693
• Manufacturer: Analog Devices

Specifications of AD7693

• Resolution (bits): 16bit
• # Chan: 1
• Sample Rate: 500kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p,Bip (Vref) x 2
• Adc Architecture: SAR
• Pkg Type: CSP,SOP

Table 8. Recommended Driver Amplifiers
Amplifier
ADA4941-1
ADA4841-x
AD8655
AD8021
AD8022
OP184
AD8605,
SINGLE-ENDED-TO-DIFFERENTIAL DRIVER
For applications using a single-ended analog signal, either
bipolar or unipolar, the
driver allows for a differential input into the part. The
schematic is shown in Figure 31.
R1 and R2 set the attenuation ratio between the input range and
the ADC range (V
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 V
supply is desired, it can be set slightly above V
some headroom for the
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.
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
a 10 μF (X5R, 0805 size) ceramic chip capacitor is appropriate
for optimum performance.
±10V, ±5V, ...
AD8615
100nF
100nF
R5
R3
Figure 31. Single-Ended-to-Differential Driver Circuit
R1
REF
R6
R4
Typical Application
Very low noise, low power single to differential
Very low noise, small, and low power
5 V single supply, low noise
Very low noise and high frequency
Low noise and high frequency
Low power, low noise, and low frequency
5 V single supply, low power
). R1, R2, and C
+5.2V
R2
C
F
ADA4941-1
ADA4941-1
ADA4941
33Ω
33Ω
single-ended-to-differential
output stage. For example,
2.7nF
2.7nF
F
AD8031
are chosen depending on
REF
10µF
/2; however, if single
IN+
IN–
REF
or the AD8605),
GND
REF
/2 to provide
AD7693
+5V REF
+5.2V
VDD
Rev. A | Page 15 of 24
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
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 32.
The AD7693 powers down automatically at the end of each
conversion phase; therefore, the operating currents and power
scale linearly with the sampling rate (refer to Figure 21). This
makes the part ideal for low sampling rates (even of a few hertz)
and low battery-powered applications.
100
95
90
85
80
75
70
65
60
55
50
1
Figure 32. PSRR vs. Frequency
10
FREQUENCY (kHz)
100
ADR43x
1000
VREF = 5V
and
AD7693
10000
ADR44x