EVAL-AD7763EBZ Analog Devices Inc, EVAL-AD7763EBZ Datasheet - Page 23

• Manufacturer Part Number: EVAL-AD7763EBZ
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD7763EBZ

• Lead Free Status / Rohs Status: Supplier Unconfirmed

SUPPLY DECOUPLING
Every supply pin must be connected to the appropriate supply
via a ferrite bead and decoupled to the correct ground pin with
a 100 nF, 0603 case size, X7R dielectric capacitor. There are two
exceptions
• Pin 12 (AV
• Pin 27 (AV
The ferrite beads that are used to connect each supply pin to the
appropriate power supply should have a characteristic impedance
of 600 Ω to 1 MΩ at frequencies around 100 MHz, a dc impedance
of 1 Ω or less, and a rated current of 200 mA.
ADDITIONAL DECOUPLING
There are two other decoupling pins on the AD7763: Pin 8
(DECAPA) and Pin 30 (DECAPB). Pin 8 should be decoupled
with a 100 nF capacitor, and Pin 30 requires a 33 pF capacitor.
REFERENCE VOLTAGE FILTERING
A low noise reference source, such as the ADR431 (2.5 V) or
ADR434 (4.096 V), is suitable for use with the AD7763. The
reference voltage supplied to the AD7763 should be decoupled
and filtered, as shown in Figure 36.
The recommended scheme for the reference voltage supply
is a 100 Ω series resistor connected to a 100 μF tantalum
capacitor, followed by a series resistor of 10 Ω, and finally, a
10 nF decoupling capacitor very close to the V
12V
the pin and a 10 nF decoupling capacitor.
capacitor or a direct connection to the supply; instead,
it is connected to Pin 14 via an 8.2 nH inductor.
10μF
C15
+
100nF
DD4
DD2
C9
) must have a 10 Ω resistor inserted between
) does not require a separate decoupling
Figure 36. Reference Connection
2
+VIN
ADR434
GND
4
U3
VOUT
6
100nF
C10
100μF
100Ω
R30
C11
+
REF
10Ω
10nF
R17
C46
pin.
PIN 10
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DIFFERENTIAL AMPLIFIER COMPONENTS
The correct components for use around the on-chip differential
amplifier are shown in Table 10. Matching the components on
both sides of the differential amplifier is important to minimize
distortion of the signal applied to the amplifier. A tolerance of
0.1% or better is required for these components. Symmetrical
routing of the tracks on both sides of the differential amplifier
also assists in achieving stated performance.
EXPOSED PADDLE
The AD7763 64-lead TQFP_EP employs a 6 mm × 6 mm exposed
paddle (see Figure 39). The paddle reduces the thermal
resistance of the package by providing a path of low thermal
resistance to the PCB and, in turn, increases the heat transfer
efficiency from the AD7763 package. Soldering the exposed
paddle to the AGND plane of the PCB is fundamental in
creating the conditions that allow the AD7763 package to
perform to the highest specifications possible.
LAYOUT CONSIDERATIONS
While using the correct components is essential to achieve
optimum performance, the correct layout is just as important.
The Design Tools section of the AD7763 product page on
the Analog Devices website contains the Gerber files for the
AD7763 evaluation board. These files should be used as a
reference when designing any system using the AD7763.
The location and orientation of some of the components
mentioned in previous sections are critical, and particular
attention must be paid to the components that are located close
to the AD7763. Locating these components farther away from
the devices can have a direct impact on the maximum
performance achievable.
The use of ground planes should also be carefully considered.
To ensure that the return currents through the decoupling
capacitors are flowing to the correct ground pin, the ground
side of the capacitors should be as close as possible to the ground
pin associated with that supply. A ground plane should not be
relied upon as the sole return path for decoupling capacitors,
because the return current path using ground planes is not
easily predicted.
AD7763