Electronic – PCB GND Guard ring

emcpcbstep-upswitching

In my design I am using the step-up converter TLV61046a. As this is the switching device, I would like to maximize EMI reduction. I would like to hear your advice if this GND guard ring in my layout make any sense in EMI reduction. The following are the pictures of the step-up converter part:

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The idea for the GND guard ring comes from the MCU 32768Hz crystal layout tips, but I am not sure if this can make any good for my application. It is just me experimenting, not official advice. Should I leave it, or remove it?

Best Answer

If you have a ground plane, then the guard ring will have little impact. Guard rings are usually to protect high impedance inputs like specialized op-amps, not so much for EMI radiation.

National Semiconductor Application Note 241

ELECTRICAL GUARDING

The effects of board leakage can be minimized using an old trick known as guarding. Here the input circuitry is surrounded by a conductive trace that is connected to a low impedance point at the same potential as the inputs. The electrical connection of the guard for the basic op amp configurations is shown in Figure 5. The guard absorbs the leakage from other points on the board, drastically reducing that reaching the input circuitry. To be completely effective, there should be a guard ring on both sides of the printed-circuit board. It is still recommended for single-sided boards, but what happens on the unguarded side is difficult to analyze unless Teflon inserts are used on the input leads. Further, although surface leakage can be virtually eliminated, the reduction in bulk leakage is much less. The reduction in bulk leakage for double-sided guarding is about an order of magnitude, but this depends on board thickness and the width of the guard ring. If there are bulk leakage problems, Teflon inserts on the through holes and Teflon or kel-F standoffs for terminations can be used. These two materials have excellent surface properties without surface treatment even in high-humidity environments. enter image description here

In fact, if you have the guard ring close to a high current node, it can pick up that noise and radiate it like an antenna.

Again, for best EMI performance, a good solid ground plane, with lots of ground via connections is best. eg. Don't use a single 20mil via when you can use two or three 10 mill vias.

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