AD7683BRM Analog Devices Inc, AD7683BRM Datasheet - Page 13

• Manufacturer Part Number: AD7683BRM
• Description: IC ADC 16BIT 100KSPS 8-MSOP
• Manufacturer: Analog Devices Inc
• Series: PulSAR®r

Specifications of AD7683BRM

• Number Of Bits: 16
• Sampling Rate (per Second): 100k
• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 6mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-TSSOP, 8-MSOP (0.118", 3.00mm Width)
• For Use With: EVAL-AD7683CBZ - BOARD EVALUATION FOR AD7683
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

TYPICAL CONNECTION DIAGRAM
Figure 22 shows an example of the recommended application
diagram for the AD7683.
ANALOG INPUT
Figure 23 shows an equivalent circuit of the input structure of
the AD7683. The two diodes, D1 and D2, provide ESD protec-
tion for the analog inputs, +IN and −IN. Care must be taken to
ensure that the analog input signal never exceeds the supply rails
by more than 0.3 V because this causes these diodes to become
forward-biased and start conducting current. However, these
diodes can handle a forward-biased current of 130 mA maximum.
For instance, these conditions can eventually occur when the
input buffer (U1) supplies are different from VDD. In such a
case, use an input buffer with a short-circuit current limitation
to protect the part.
This analog input structure allows the sampling of the differen-
tial signal between +IN and −IN. By using this differential input,
small signals common to both inputs are rejected. For instance,
by using −IN to sense a remote signal ground, ground potential
differences between the sensor and the local ADC ground are
eliminated. During the acquisition phase, the impedance of the
analog input, +IN, can be modeled as a parallel combination of
Capacitor C
of R
600 Ω and is a lumped component consisting of some serial
resistors and the on resistance of the switches. C
30 pF and is mainly the ADC sampling capacitor. During the
conversion phase, when the switches are opened, the input
impedance is limited to C
IN
OR –IN
GND
and C
+IN
PIN
IN
. C
Figure 23. Equivalent Analog Input Circuit
and the network formed by the series connection
PIN
C
is primarily the pin capacitance. R
PIN
VDD
PIN
D1
D2
0V TO V
. R
NOTES
1. SEE VOLTAGE REFERENCE INPUT SECTION FOR REFERENCE SELECTION.
2. C
3. SEE DRIVER AMPLIFIER CHOICE SECTION.
4. OPTIONAL FILTER. SEE ANALOG INPUT SECTION.
IN
REF
and C
REF
IS USUALLY A 10µF CERAMIC CAPACITOR (X5R).
(NOTE 3)
IN
R
make a 1-pole, low-
IN
(NOTE 1)
IN
REF
C
(NOTE 4)
2.7nF
33Ω
IN
is typically
IN
Figure 22. Typical Application Diagram
2.2µF TO 10µF
is typically
(NOTE 2)
C
Rev. A | Page 13 of 16
REF
+IN
–IN
REF
GND
AD7683
pass filter that reduces undesirable aliasing effects and limits
the noise.
When the source impedance of the driving circuit is low, the
AD7683 can be driven directly. Large source impedances signi-
ficantly affect the ac performance, especially THD. The dc
performances are less sensitive to the input impedance.
DRIVER AMPLIFIER CHOICE
Although the AD7683 is easy to drive, the driver amplifier
needs to meet the following requirements:
•
•
•
Table 10. Recommended Driver Amplifiers
Amplifier
ADA4841
OP184
AD8605,
AD8519
AD8031
VDD
DCLOCK
The noise generated by the driver amplifier needs to be
kept as low as possible to preserve the SNR and transition
noise performance of the AD7683. Note that the AD7683
has a noise figure much lower than most other 16-bit
ADCs and, therefore, can be driven by a noisier op amp
while preserving the same or better system performance.
The noise coming from the driver is filtered by the AD7683
analog input circuit, 1-pole, low-pass filter made by R
and C
For ac applications, the driver needs to have a THD
performance suitable to that of the AD7683. Figure 15
shows the THD vs. frequency that the driver should
exceed.
For multichannel multiplexed applications, the driver
amplifier and the AD7683 analog input circuit must be
able to settle for a full-scale step of the capacitor array at a
16-bit level (0.0015%). In the amplifier data sheet, settling
at 0.1% to 0.01% is more commonly specified. This could
differ significantly from the settling time at a 16-bit level
and should be verified prior to driver selection.
D
OUT
AD8615
CS
IN
100nF
or by the external filter, if one is used.
3-WIRE INTERFACE
Typical Application
Very low noise and low power
Low power, low noise, and low frequency
5 V single-supply, low power
Low power and low frequency
High frequency and low power
2.7V TO 5.25V
AD7683
IN