AD9650-105EBZ Analog Devices Inc, AD9650-105EBZ Datasheet - Page 43

• Manufacturer Part Number: AD9650-105EBZ
• Description: 16Bit Hi SNR 105 Msps Dual ADC
• Manufacturer: Analog Devices Inc

Specifications of AD9650-105EBZ

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
DESIGN GUIDELINES
Before starting design and layout of the AD9650 as a system,
it is recommended that the designer become familiar with these
guidelines, which discuss the special circuit connections and
layout requirements that are needed for certain pins.
Power and Ground Recommendations
When connecting power to the AD9650, it is recommended that
two separate 1.8 V supplies be used. Use one supply for the analog
outputs (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
AD9650. With proper decoupling and smart partitioning of the
PCB analog, digital, and clock sections, optimum performance
is easily achieved.
LVDS Operation
The AD9650 defaults to CMOS output mode on power-up.
If LVDS operation is desired, this mode must be programmed,
using the SPI configuration registers after power-up. When the
AD9650 powers up in CMOS mode with LVDS termination
resistors (100 Ω) on the outputs, the DRVDD current can be
higher than the typical value until the part is placed in LVDS
mode. This additional DRVDD current does not cause damage
to the AD9650, but it should be taken into account when consid-
ering the maximum DRVDD current for the part.
To avoid this additional DRVDD current, the AD9650 outputs
can be disabled at power-up by taking the OEB pin high. After
the part is placed in LVDS mode via the SPI port, the OEB pin
can be taken low to enable the outputs.
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
AD9650 exposed paddle, Pin 0.
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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 to
prevent solder wicking through the vias, which can compromise
the connection.
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. For detailed
information about packaging and PCB layout of chip scale
packages, see the
Manufacturing Guide for the Lead Frame Chip Scale Package
(LFCSP), at www.analog.com.
VCM
The VCM pin should be decoupled to ground with a 0.1 μF
capacitor, as shown in Figure 80.
RBIAS
The AD9650 requires that a 10 kΩ resistor be placed between
the RBIAS pin and ground. This resistor sets the master current
reference of the ADC core and should have at least a 1% tolerance.
Reference Decoupling
The VREF pin should be externally decoupled 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
AD9650 to keep these signals from transitioning at the converter
inputs during critical sampling periods.
AN-772
Application Note, A Design and
AD9650