AD7193 Analog Devices, AD7193 Datasheet - Page 53

• Manufacturer Part Number: AD7193
• Description: 4-Channel, 4.8 kHz, Ultralow Noise, 24-Bit Sigma-Delta ADC with PGA
• Manufacturer: Analog Devices

Specifications of AD7193

• Resolution (bits): 24bit
• # Chan: 4
• Sample Rate: n/a
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni,SE-Uni,Usr-Defined Range/Offset
• Ain Range: ± (Vref/Gain)
• Adc Architecture: Sigma-Delta
• Pkg Type: SOP

Data Sheet
GROUNDING AND LAYOUT
Because the analog inputs and reference inputs are differential,
most of the voltages in the analog modulator are common-mode
voltages. The high common-mode rejection of the part removes
common-mode noise on these inputs. The analog and digital
supplies to the AD7193 are independent and separately pinned
out to minimize coupling between the analog and digital sections
of the device. The digital filter provides rejection of broadband
noise on the power supplies, except at integer multiples of the
modulator sampling frequency.
Connect an RC filter to each analog input pin to provide rejection
at the modulator sampling frequency. A 100 Ω resistor in series
with each analog input, a 0.1 µF capacitor between the analog
input pins, and a 0.01 µF capacitor from each analog input to
AGND are advised.
The digital filter also removes noise from the analog and
reference inputs provided that these noise sources do not
saturate the analog modulator. As a result, the AD7193 is
more immune to noise interference than a conventional high
resolution converter. However, because the resolution of the
AD7193 is so high and the noise levels from the converter so
low, care must be taken with regard to grounding and layout.
The printed circuit board (PCB) that houses the ADC must be
designed so that the analog and digital sections are separated
and confined to certain areas of the board. This facilitates the
use of ground planes that can be easily separated. A minimum
etch technique is generally best for ground planes because it
gives the best shielding.
Although the AD7193 has separate pins for analog and digital
ground, the AGND and DGND pins are tied together internally
via the substrate. Therefore, the user must not tie these two pins
to separate ground planes unless the ground planes are connected
together near the AD7193.
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In systems in which the AGND and DGND are connected some-
where else in the system (that is, the power supply of the system),
they should not be connected again at the AD7193 because a
ground loop results. In these situations, it is recommended that
the ground pins of the AD7193 be tied to the AGND plane.
In any layout, the user must keep in mind the flow of currents
in the system, ensuring that the paths for all currents are as close as
possible to the paths the currents took to reach their destinations.
Avoid forcing digital currents to flow through the AGND.
Avoid running digital lines under the device because this couples
noise onto the die and allows the analog ground plane to run
under the AD7193 to prevent noise coupling. The power supply
lines to the AD7193 must use as wide a trace as possible to
provide low impedance paths and reduce the effects of glitches
on the power supply line. Shield fast switching signals like clocks
with digital ground to prevent radiating noise to other sections
of the board and never run clock signals near the analog inputs.
Avoid crossover of digital and analog signals. Run traces on
opposite sides of the board at right angles to each other. This
reduces the effects of feedthrough through the board. A microstrip
technique is by far the best but is not always possible with a
double-sided board. In this technique, the component side of
the board is dedicated to ground planes, whereas signals are
placed on the solder side.
Good decoupling is important when using high resolution ADCs.
Decouple all analog supplies with 10 µF tantalum capacitors in
parallel with 0.1 µF capacitors to AGND. To achieve the best
results from these decoupling components, place them as close
as possible to the device, ideally right up against the device.
Decouple all logic chips with 0.1 µF ceramic capacitors to DGND.
In systems in which a common supply voltage is used to drive
both the AV
that the system AV
recommended analog supply decoupling capacitors between the
AV
digital supply decoupling capacitor between the DV
AD7193 and DGND.
DD
pin of the AD7193 and AGND and the recommended
DD
and DV
DD
supply be used. For this supply, place the
DD
of the AD7193, it is recommended
DD
AD7193
pin of the