AD9643 Analog Devices, AD9643 Datasheet - Page 35

• Manufacturer Part Number: AD9643
• Description: 14-Bit, 170/210/250 MSPS, 1.8 V Dual Analog-to-Digital Converter (ADC)
• Manufacturer: Analog Devices

Specifications of AD9643

• Resolution (bits): 14bit
• # Chan: 2
• Sample Rate: 250MSPS
• Interface: LVDS,Par
• Analog Input Type: Diff-Bip
• Ain Range: 1.75 V p-p
• Adc Architecture: Pipelined
• Pkg Type: CSP

Data Sheet
APPLICATIONS INFORMATION
DESIGN GUIDELINES
Before starting system level design and layout of the AD9643,
it is recommended that the designer become familiar with these
guidelines, which discuss the special circuit connections and
layout requirements needed for certain pins.
Power and Ground Recommendations
When connecting power to the AD9643, it is recommended
that two separate 1.8 V supplies be used: one supply should be
used for analog (AVDD), and a separate supply should be used
for the digital outputs (DRVDD). The designer can employ
several different decoupling capacitors to cover both high and
low frequencies. These capacitors should be located close to the
point of entry at the PC board level and close to the pins of the
part with minimal trace length.
A single PCB ground plane should be sufficient when using the
AD9643. With proper decoupling and smart partitioning of the
PCB analog, digital, and clock sections, optimum performance
is easily achieved.
Exposed Paddle Thermal Heat Slug Recommendations
It is mandatory that the exposed paddle on the underside of the
ADC be connected to analog ground (AGND) to achieve the
best electrical and thermal performance. A continuous, exposed
(no solder mask) copper plane on the PCB should mate to the
AD9643 exposed paddle, Pin 0.
The copper plane should have 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 filled or plugged with
nonconductive epoxy.
To maximize the coverage and adhesion between the ADC
and the PCB, a silkscreen should be overlaid to partition the
continuous plane on the PCB into several uniform sections.
This provides several tie points between the ADC and the PCB
during the reflow process. Using one continuous plane with no
partitions guarantees only one tie point between the ADC and
the PCB. See the evaluation board for a PCB layout example.
For detailed information about the packaging and PCB layout
of chip scale packages, refer to the
Design and Manufacturing Guide for the Lead Frame Chip Scale
Package (LFCSP).
AN-772 Application
Note, A
Rev. B | Page 35 of 36
VCM
The VCM pin should be decoupled to ground with a 0.1 μF
capacitor, as shown in Figure 48. For optimal channel-to-channel
isolation, a 33 Ω resistor should be included between the AD9643
VCM pin and the Channel A analog input network connection,
as well as between the AD9643 VCM pin and the Channel B
analog input network connection.
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
AD9643 to keep these signals from transitioning at the converter
input pins during critical sampling periods.
AD9643