AD7690 Analog Devices, AD7690 Datasheet - Page 15

• Manufacturer Part Number: AD7690
• Manufacturer: Analog Devices

Specifications of AD7690

• Resolution (bits): 18bit
• # Chan: 1
• Sample Rate: 400kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p
• Adc Architecture: SAR
• Pkg Type: CSP,SOP

•
•
Table 8. Recommended Driver Amplifiers
Amplifier
ADA4941-1
ADA4841-x
AD8655
AD8021
AD8022
OP184
AD8605,
SINGLE-TO-DIFFERENTIAL DRIVER
For applications using a single-ended analog signal, either bipolar
or unipolar, the
allows for a differential input into the part. The schematic is
shown in Figure 30.
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.
For ac applications, the driver should have a THD
performance commensurate with the AD7690.
For multichannel multiplexed applications, the driver
amplifier and the AD7690 analog input circuit must settle
for a full-scale step onto the capacitor array at an 18-bit
level (0.0004%, 4 ppm). In the amplifier’s data sheet, settling
at 0.1% to 0.01% is more commonly specified. This may
differ significantly from the settling time at an 18-bit level
and should be verified prior to driver selection.
AD8615
ADA4941-1
REF
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
ADA4941-1
single-ended-to-differential driver
output stage. For example,
F
are chosen depending on
REF
/2; however, if single
REF
/2 to provide
Rev. B | Page 15 of 24
VOLTAGE REFERENCE INPUT
The AD7690 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.
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 a low temperature drift
If desired, a reference-decoupling capacitor with a value as small
as 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.
±10V, ±5V, ...
100nF
100nF
R5
R3
Figure 30. Single-Ended-to-Differential Driver Circuit
R1
R6
R4
+5.2V
R2
C
F
ADA4941
15Ω
15Ω
2.7nF
2.7nF
AD8031
10µF
ADR43x
IN+
IN–
or the AD8605),
GND
REF
AD7690
AD7690
reference.
+5V REF
+5.2V
VDD