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chitransh92 , 05-31-2019, 03:30 AM

Hello,

I am working on a low speed PCB which is based on PIC micro controller running on 16 MHz crystal.
This PCB has FET devices and big inductors of 22uH and has CAN and USB as external interfaces.

W.r.t to my layout where i am trying to keep same net pads together as shown in the attached figure, the question is "Shall these pads be connected using a polygon or tracks??"
Please note it is small board of 4x4 inch and layout is similar to above pads with same nets are close by.

Please suggest with Rationale if possible..

Thank you.

robertferanec , 06-01-2019, 01:31 AM

For digital signals I normally use tracks. For powers and high current connections I use wide tracks or preferably polygons. Analogue signals - it depends if they need to have specific impedance (depends on PCB stackup) or they need to be low impedance (wider than digital tracks).

In your case it is very hard to tell what is this net about (it doesn't have a proper net name). What is the signal?

chitransh92 , 06-05-2019, 03:51 PM

The layout components are passives for the GATE driver circuit of a MOSFET.
For my design there is not such requirement of Impedance matching...

Thank you.

Related question :
SO far I have seen Impedance matching in the tracks and Vias however have not come accross the impedance matching polygons.
@robertferanec could you elaborate on this please....

Lakshmi , 06-07-2019, 08:25 AM

- You said you have USB and CAN Bus..
USB (differential pair) has to be matched to 90ohm impedance and am not sure about CAN bus. Read up about that or Check for some reference guidelines.
- As robert suggested use Track/Trace for Signals and Use Planes for Power(VCC and GND).

robertferanec , 06-09-2019, 02:34 AM

- It's not really about MATCHING impedance for powers. Just for powers you also would like to follow some properties of the connections and in most cases, you would like to keep impedance of powers as low as possible (low impedance on powers means that power circuit and power layout is going to react very quickly to power changes).