How to use contain layer of imitate ground connection (AGND) and layer of power ground connection (the switch manostat of PGND) ? This is a question that the meeting when a lot of development staff are designing switch power source asks. Staff of a few development already was used to handling layer of digital ground connection and layer of imitate ground connection; However, when involving power GND, their experience often is met invalidation. Stylist can duplicate directly normally the circuit that chooses switch manostat board layout, ponder over this problem no longer.

PGND is taller pulse electric current sorts the ground connection link of classics. According to switch manostat develop attacks structure, the electric current that this expresses to pass power transistor or power driver the pulse electric current of class. The switch control that exterior to containing switch provides implement, it is important to should receive layer blame to be.

AGND is called sometimes SGND (layer of signal ground connection) , it is other signal uses as the ground connection join that consult, normally very quiet. Layer of this ground connection includes to adjust the in-house and fiducial voltage that output voltage place needs. Soft start and make can voltage also is with AGND join consult.

About processing of connective of these two kinds of ground connection, have two kinds of different technology point of views, because the opinion of this expert also produced difference.

Basis among them a kind of viewpoint, the AGND on IC and PGND join should be in switch manostat to make the appearance other the foot severally each other join. Come so, two bring the voltage deflection between the foot to maintain in relatively inferior level. Because this can protect switch manostat,IC is avoided suffer interference, spare then destroy. All ground connection of circuit join and likely ground connection layer joins the structure that attacks with star develop this are bit more communal. The graph shows the implementation give a demonstration that is this viewpoint 1 times. The circuit that showed LTM4600 here board layout. This is module of step-down of a 10A miniature. The independent ground connection on circuit board joins each other lean together (refer to a graph please 1 medium blue is elliptic) . As a result of the parasitism inductance of the respective solder line between chip and crust, and the inductance that cites a base severally, because this has been put in the PGND of certain level and AGND,go Ou, this brings about chip electrify a few mutual interference exist between the road.

Graph 1: Solder contact nods the local link that manages PGND and AGND.

Another kind of viewpoint is will the AGND on circuit board and PGND are apart, form two alone ground connection layers, mutual join is nodded in some. Pass this kind of join, interference signal (voltage deflection) basically appear in PGND area, and the voltage of AGND area still unusual calm, go from PGND well Ou. However, change according to twinkling of pulse electric current and voltaic strength condition, the likelihood is put in apparent voltage deflection between the PGND that brings a foot to go up severally and AGND. This may bring about switch manostat IC cannot work normally, damage even. The graph shows the implementation plan that is this viewpoint 2 times. This give typical examples uses ADP2386 of manostat of step-down of a 6A switch.

Graph 2: Apart AGND and PGND had used Kong Lian to receive in lower part of ground connection label.

In the final analysis, ground connection problem is balance advantages and disadvantages actually: Part layer of two ground connection has the advantage that keeps apart noise and interference; But voltage deflection may arise between layer of two ground connection, be put in attaint chip thereby and affect functional risk. After balance advantages and disadvantages, final and decision-making basically depended on correctly IC design, the latch risk that every the parasitism inductance that includes switch to change line of n of speed, power, solder and IC to seal mount, IC designs (involve different semiconductor technology) .

Conclusion

About how handling the issue of AGND and PGND ground connection, do not have simple answer. So relevant discussion still continueing. I am mentioned in front, the circuit in the circuit of give typical examples that a lot of switch manostat users use IC manufacturer to offer board layout and type of ground connection join. Such doing very useful, because you can assume normally,manufacturer also used this configuration to have a test to each IC. And, in the graph 1 with the graph can see in 2 offerred give a demonstration, respective IC brings a foot to arrange apply to the join of local ground connection by PGND and AGND, perhaps apply to alone ground connection.

Of course, IC manufacturer may make mistake when designing circuit of give typical examples. So, had better know the more news of relevant fundamental further.