ADS5547 datasheet(45/57 Pages) TI

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Board Design Considerations

Grounding

Supply Decoupling

Series Resistors on Data Outputs

Exposed Thermal Pad

ADS5527

SLWS196A – DECEMBER 2006 – REVISED MAY 2007

A single ground plane is sufficient to give good performance, provided the analog, digital and clock sections of

the board are cleanly partitioned. Refer to the EVM User Guide (SLWU028) for details on layout and grounding.

As the ADS5527 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 3.3V 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.

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.

It is necessary to solder the exposed pad at the bottom of the package to a ground plane for best thermal

performance. For detailed information, see application notes QFN Layout Guidelines (SLOA122) and

QFN/SON PCB Attachment (SLUA271).

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ADS5547 Datasheet(PDF) 45 Page - Texas Instruments