AD7667 Datasheet, PDF (22/23 Pages) Analog Devices – 16-Bit 1 MSPS SAR Unipolar ADC with Ref

AD7667
PRELIMINARY TECHNICAL DATA
at right angles to each other. This will reduce the effect of
feedthrough through the board.
The power supplies lines to the AD7667 should use as
large trace as possible to provide low impedance paths and
reduce the effect of glitches on the power supplies lines.
Good decoupling is also important to lower the supplies
impedance presented to the AD7667 and reduce the magni-
tude of the supply spikes. Decoupling ceramic capacitors,
typically 100 nF, should be placed on each power supplies
pins AVDD, DVDD, and OVDD close to, and ideally right
up against, these pins and their corresponding ground pins.
Additionally, low ESR 10 µF capacitors should be located in
the vicinity of the ADC to further reduce low frequency
ripple.
The DVDD supply of the AD7667 can be either a separate
supply or come from the analog supply AVDD or the digi-
tal interface supply OVDD. When the system digital supply
is noisy, or fast switching digital signals are present, it is
recommended that if no separate supply available, connect
the DVDD digital supply to the analog supply, AVDD,
through an RC filter as shown in Figure 5, and connect
the system supply to the interface digital supply, OVDD,
and the remaining digital circuitry. When DVDD is powered
from the system supply, it is useful to insert a bead to fur-
ther reduce high-frequency spikes.
The AD7667 has five different ground pins: INGND, REF-
GND, AGND, DGND, and OGND. INGND is used to
sense the analog input signal. REFGND senses the refer-
ence voltage and should be a low impedance return to the
reference because it carries pulsed currents. AGND is the
ground to which most internal ADC analog signals are
referenced. This ground must be connected with the least
resistance to the analog ground plane. DGND must be
tied to the analog or digital ground plane depending on the
configuration. OGND is connected to the digital system
ground.
Evaluating the AD7667 Performance
A recommended layout for the AD7667 is outlined in the
evaluation board for the AD7667. The evaluation board
package includes a fully assembled and tested evaluation
board, documentation, and software for controlling the board
from a PC via the Eval-Control Board.
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REV. PrA