AD12401SLASHKIT datasheet(26/28 Pages) AD

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AD12401

Rev. A | Page 26 of 28

LAYOUT GUIDELINES

The AD12401 requires a different approach from traditional

high speed ADC system layouts. While the AD12401’s internal

PCB isolates digital and analog grounds, these planes are tied

together through the product’s aluminum case structure.

Therefore, the decision to isolate the analog and digital grounds

on the system PCB has additional factors to consider.

For example, if the AD12401 is attached with conductive

thermal interface material to the system PCB, there is

essentially no benefit to keeping the analog and digital ground

planes separate. If neither thermal interface material nor

nonconductive interface material is used, system architects

must consider the ground loop that is created if analog and

digital planes are tied together directly under the AD12401.

This EMI-based decision must be considered on a case-by-case

basis and is largely dependent on the other sources of EMI in

the system. One critical consideration is that a 12-bit perform-

ance requirement (–74 dBc) requires keeping conducted EMI

currents (referenced to the input of the AD12401) below 4.5 μA.

All the characterization and testing of the AD12401 is performed

using a system that isolated these ground planes.

If thermal interface material is used in the final system design,

the following layout factors need to be considered: open solder

mask on the area that contacts the interface material and the

thickness of the ground plane. While this should be analyzed in

each specific system design, the use of solder mask can negate

any advantage achieved by using the thermal interface material,

and its use should be carefully considered. The ground plane

thickness does not have a major impact on the thermal per-

formance, but if design margin is slight, additional thickness

can yield incremental improvements.

PCB INTERFACE

Figure 38 provides the mounting hole footprint for assembling

the AD12401 to the second-level assembly. The diagram is

referenced to the center of the mating QTE connector. Refer to

the QTE/QSE series connector documentation at www.samtec.com

for the SMT footprint of the mating connector.

The top view of the second-level assembly footprint provides a

diagram of the second-level assembly locating tab locations for

mating the Samtec QTE-060-01-L-A-K-TR terminal strip on

the AD12401 to a QSE-060-01-L-A-K-TR socket on the second-

level assembly. The diagram is referenced to the center of the

QTE terminal strip on the AD12401 and the mounting holds

for the screws, which holds the AD12401 to the second-level

assembly board. The relationship of these locating tabs is based

on information provided by Samtec (connector supplier) and

should be verified with Samtec by the customer.

Mating and unmating forces—the knifing or peeling action of

applying force to one end or one side—must be avoided to

prevent damage to the connector and guidepost.

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