ADS5545_13 Datasheet, PDF (47/59 Pages) Texas Instruments – 14-BIT, 170 MSPS ADC WITH DDR LVDS/CMOS OUTPUTS

ADS5545
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Board Design Considerations
SLWS180C – NOVEMBER 2005 – REVISED MAY 2007
Grounding
A single ground plane is sufficient to give good performance, provided the analog, digital and clock sections of
the board are cleanly partitioned. See the EVM User Guide (SLWU028) for details on layout and grounding.
Supply Decoupling
As the ADS5546 already includes internal decoupling, minimal external decoupling can be used without loss in
performance. Note that decoupling capacitors can help to filter external power supply noise, so the optimum
number of capacitors would depend on the actual application. The decoupling capacitors should be placed very
close to the converter supply pins.
It is recommended to use separate supplies for the analog and digital supply pins to isolate digital switching
noise from sensitive analog circuitry. In case only a single 3.3-V supply is available, it should be routed first to
AVDD. It can then be tapped and isolated with a ferrite bead (or inductor) with decoupling capacitor, before
being routed to DRVDD.
Series Resistors on Data Outputs
It is recommended to put series resistors (50 to 100 Ω) on each output line placed very close to the converter
pins. This helps to isolate the outputs from seeing large load capacitances and in turn reduces the amount of
switching noise.
Exposed Thermal Pad
For best thermal performance, it is necessary to solder the exposed pad at the bottom of the package to a
ground plane using multiple vias. For detailed information, see application notes QFN Layout Guidelines
(SLOA122) and QFN/SON PCB Attachment (SLUA271).
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