ADS5424IPGPR datasheet(21/29 Pages) TI2

21 / 29 page

ADS5424

SLWS157B − JANUARY 2005 − REVISED JANUARY 2010

www.ti.com

APPLICATION INFORMATION

The ADS5424 uses two power supplies. For the analog

portion of the design, a 5 V AVDD is used, while for the

digital outputs supply (DRVDD), we recommend the use

of 3.3 V. All the ground pins are marked as GND,

although AGND pins and DRGND pins are not tied

together inside the package. Customers willing to

experiment with different grounding schemes should

know that AGND pins are 4, 7, 10, 13, 15, 17, 19, 21,

23, 25, 27, and 29, while DRGND pins are 2, 34, and 42.

Nevertheless, we recommend that both grounds are

tied together externally, using a common ground plane.

That is the case on the production test boards and

modules provided to customer for evaluation. In order

to obtain the best performance, user should layout the

board to assure that the digital return currents do not

flow under the analog portion of the board. This can be

achieved without the need to split the board and just

with careful component placing and increasing the

number of vias and ground planes.

Finally, notice that the metallic heat sink under the

package is also connected to analog ground.

LAYOUT INFORMATION

The evaluation board represents a good guideline of

how to layout the board to obtain the maximum

performance out of the ADS5424. General design rules

as the use of multilayer boards, single ground plane for

both, analog and digital ADC ground connections and

local decoupling ceramic chip capacitors should be

applied. The input traces should be isolated from any

external source of interference or noise, including the

digital outputs as well as the clock traces. Clock should

also be isolated from other signals, especially on

applications where low jitter is required, as high IF

sampling.

Besides performance oriented rules, special care has

to be taken when considering the heat dissipation out

of the device. The thermal heat sink (octagonal, with

2,5 mm on each side) should be soldered to the board,

and provision for more than 16 ground vias should be

made. The thermal package information describes the

TJA values obtained on the different configurations.

ADS5424IPGPR Datasheet(PDF) 21 Page - Texas Instruments

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