AD9653BCPZ-125 Analog Devices, AD9653BCPZ-125 Datasheet - Page 39

• Manufacturer Part Number: AD9653BCPZ-125
• Description: the ad9653 is a quad, 16-bit, 125 msps analog-to-digital converter (adc) with an...
• Manufacturer: Analog Devices

Data Sheet
APPLICATIONS INFORMATION
DESIGN GUIDELINES
Before starting design and layout of the
it is recommended that the designer become familiar with these
guidelines, which describes the special circuit connections and
layout requirements that are needed for certain pins.
POWER AND GROUND RECOMMENDATIONS
When connecting power to the AD9653, it is recommended
that two separate 1.8 V supplies be used. Use one supply for
analog (AVDD); use a separate supply for the digital outputs
(DRVDD). For both AVDD and DRVDD, several different
decoupling capacitors should be used to cover both high and
low frequencies. Place these capacitors close to the point of
entry at the PCB level and close to the pins of the part, with
minimal trace length.
A single PCB ground plane should be sufficient when using the
AD9653. With proper decoupling and smart partitioning of the
PCB analog, digital, and clock sections, optimum performance
is easily achieved.
EXPOSED PAD THERMAL HEAT SLUG
RECOMMENDATIONS
It is required that the exposed pad on the underside of the ADC
be connected to analog ground (AGND) to achieve the best
electrical and thermal performance of the AD9653. An exposed
continuous copper plane on the PCB should mate to the
AD9653
several vias to achieve the lowest possible resistive thermal path
for heat dissipation to flow through the bottom of the PCB.
These vias should be solder-filled or plugged.
To maximize the coverage and adhesion between the ADC and
PCB, partition the continuous copper plane by overlaying a
silkscreen on the PCB into several uniform sections. This provides
several tie points between the ADC and PCB during the reflow
process, whereas using one continuous plane with no partitions
only guarantees one tie point. See Figure 76 for a PCB layout
example. For detailed information on packaging and the PCB
layout of chip scale packages, see the
A Design and Manufacturing Guide for the Lead Frame Chip
Scale Package (LFCSP), at www.analog.com.
exposed pad, Pin 0. The copper plane should have
SILKSCREEN PARTITION
PIN 1 INDICATOR
Figure 76. Typical PCB Layout
AN-772 Application
AD9653
as a system,
Note,
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VCM
The VCM pin should be bypassed to ground with a 0.1 μF
capacitor.
REFERENCE DECOUPLING
The VREF pin should be externally bypassed to ground with a
low ESR, 1.0 μF capacitor in parallel with a low ESR, 0.1 μF
ceramic capacitor.
SPI PORT
The SPI port should not be active during periods when the full
dynamic performance of the converter is required. Because the
SCLK, CSB, and SDIO signals are typically asynchronous to the
ADC clock, noise from these signals can degrade converter
performance. If the on-board SPI bus is used for other devices,
it may be necessary to provide buffers between this bus and the
AD9653
verter inputs during critical sampling periods.
CROSSTALK PERFORMANCE
The
input pairs on either corner of the chip. See Figure 6 for the pin
configuration. To maximize the crosstalk performance on the
board, add grounded filled vias in between the adjacent
channels as shown in Figure 77.
GROUNDED
FILLED VIAS
FOR ADDED
CROSSTALK
ISOLATION
VIN
CHANNEL A
AD9653
Figure 77. Layout Technique to Maximize Crosstalk Performance
VIN
CHANNEL B
to keep these signals from transitioning at the con-
is available in a 48-lead LFCSP package with the
VIN
CHANNEL C
VIN
CHANNEL D
AD9653
PIN 1