TDA2SA datasheet(343/427 Pages) TI2

343 / 427 page

SWPS040-199

343

TDA2SX, TDA2SG, TDA2SA

TDA2HG, TDA2HV, TDA2HF, TDA2LF

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SPRS951F – DECEMBER 2015 – REVISED MAY 2019

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Product Folder Links: TDA2SX TDA2SG TDA2SA TDA2HG TDA2HV TDA2HF TDA2LF

Applications, Implementation, and Layout

Routing of high-frequency clock signals on outer layers, even for a short distance, is discouraged,

because their emissions energy is concentrated at the discrete harmonics and can become significant

even with poor radiators.

Coplanar shielding of traces on outer layers (placing ground near the sides of a track along its length) is

effective only if the distance between the trace sides and the ground is smaller that the trace height above

the ground reference plane. For modern multilayer PCBs this is often not possible, so coplanar shielding

will not be effective. Do not route high-frequency traces near the periphery of the PCB, as the lack of a

ground reference near the trace edges can increase EMI: see Section 8.2.6.3, Ground Guidelines.

8.2.6.3

Ground Guidelines

8.2.6.3.1 PCB Outer Layers

Ideally the areas on the top and bottom layers of the PCB that are not enclosed by a shield should be

filled with ground after the routing is completed and connected with an adequate number of vias to the

ground on the inner ground planes.

8.2.6.3.2 Metallic Frames

Ensure that all metallic parts are well connected to the PCB ground (like LCD screens metallic frames,

antennas reference planes, connector cages, flex cables grounds, and so forth). If using flex PCB ribbon

cables to bring high-frequency signals off the PCB, ensure they are adequately shielded (coaxial cables or

flex ribbons with a solid reference ground).

8.2.6.3.3 Connectors

For high-frequency signals going to connectors choose a fully shielded connector, if possible (for example,

SD card connectors). For signals going to external connectors or which are routed over long distances, it

is recommended to reduce their bandwidth by using low-pass filters (resistor, capacitor (RC) combinations

or lossy ferrite inductors). These filters will help to prevent emissions from the board and can also improve

the immunity from external disturbances.

8.2.6.3.4 Guard Ring on PCB Edges

The major advantage of a multilayer PCB with ground-plane is the ground return path below each and

every signal or power trace.

As shown in Figure 8-18 the field lines of the signal return to PCB ground as long as an infinite ground is

available.

Traces near the PCB-edges do not have this infinite ground and therefore may radiate more than the

others. Thus, signals (clocks) or power traces (core power) identified to be critical must not be routed in

the vicinity of PCB edges, or, if not avoidable, must be accompanied by a guard ring on the PCB edge.

Figure 8-18. Field Lines of a Signal Above Ground

TDA2SA Datasheet(PDF) 343 Page - Texas Instruments

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