AD7641BSTZ Analog Devices Inc, AD7641BSTZ Datasheet - Page 27

• Manufacturer Part Number: AD7641BSTZ
• Description: IC ADC 18BIT 2MSPS SAR 48-LQFP
• Manufacturer: Analog Devices Inc

Specifications of AD7641BSTZ

• Data Interface: Serial, Parallel
• Number Of Bits: 18
• Sampling Rate (per Second): 2M
• Number Of Converters: 1
• Power Dissipation (max): 92mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• Resolution (bits): 18bit
• Sampling Rate: 2MSPS
• Input Channel Type: Differential
• Supply Current: 23mA
• Digital Ic Case Style: QFP
• No. Of Pins: 48
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD7641CBZ - BOARD EVALUATION FOR AD7641
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

APPLICATION HINTS
LAYOUT
While the AD7641 has very good immunity to noise on the
power supplies, exercise care with the grounding layout. To
facilitate the use of ground planes that can be easily separated,
design the printed circuit board that houses the AD7641 so that
the analog and digital sections are separated and confined to
certain areas of the board. Digital and analog ground planes
should be joined in only one place, preferably underneath the
AD7641, or as close as possible to the AD7641. If the AD7641 is
in a system where multiple devices require analog-to-digital
ground connections, the connections should still be made at
one point only, a star ground point, established as close as
possible to the AD7641.
To prevent coupling noise onto the die, to avoid radiating noise,
and to reduce feedthrough:
• Do not run digital lines under the device.
• Run the analog ground plane under the AD7641.
• Shield fast switching signals, like CNVST or clocks, with
• Avoid crossover of digital and analog signals.
• Run traces on different but close layers of the board, at right
The power supply lines to the AD7641 should use as large a
trace as possible to provide low impedance paths and reduce the
effect of glitches on the power supply lines. Good decoupling is
also important to lower the impedance of the supplies presented
to the AD7641, and to reduce the magnitude of the supply
spikes. Decoupling ceramic capacitors, typically 100 nF, should
be placed on each of the power supplies pins, AVDD, DVDD,
and OVDD. The capacitors should be placed 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.
digital ground to avoid radiating noise to other sections of
the board, and never run them near analog signal paths.
angles to each other, to reduce the effect of feedthrough
through the board.
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The DVDD supply of the AD7641 can be either a separate
supply or come from the analog supply, AVDD, or from the
digital interface supply, OVDD. When the system digital supply
is noisy, or fast switching digital signals are present, and no
separate supply is available, it is recommended to connect the
DVDD digital supply to the analog supply AVDD through an
RC filter, and to connect the system supply to the interface
digital supply OVDD and the remaining digital circuitry. Refer
to Figure 23 for an example of this configuration. When DVDD
is powered from the system supply, it is useful to insert a bead
to further reduce high frequency spikes.
The AD7641 has four different ground pins: REFGND, AGND,
DGND, and OGND. REFGND senses the reference voltage and,
because it carries pulsed currents, should have a low impedance
return to the reference. AGND is the ground to which most
internal ADC analog signals are referenced; it 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.
The layout of the decoupling of the reference voltage is
important. To minimize parasitic inductances, place the
decoupling capacitor close to the ADC and connect it with
short, thick traces.
EVALUATING THE AD7641 PERFORMANCE
A recommended layout for the AD7641 is outlined in the
documentation of the
the AD7641. The evaluation board package includes a fully
assembled and tested evaluation board, documentation, and
software for controlling the board from a PC via the
CONTROL
BRD3.
EVAL-AD7641-CB
evaluation board for
AD7641
EVAL-