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I've made a layout around an Allegro A4490 triple buck regulator, with four optimization goals:

  • minimize loop area/change in area when switching
  • keep the ground attachment of the input and output capacitors and the flyback diode together
  • avoid cutouts in the ground plane, and at least keep deviations for return currents short
  • prefer vias in slow signals with small current (i.e. the "enable" and "power on reset" traces)

I have two fixed voltages, and one that can be adjusted using a potentiometer; in addition the outputs can be switched individually, or a jumper can be used to keep them on, and an active-low reset signal is generated when the supply is outside the target range.

As a result, I now have a layout where a trace runs through the middle of a 0603 capacitor, which limits the trace width to 0,3mm:

Regulator PCB

  1. Do I want to change the layout so I can have wider traces, or is that irrelevant anyway because of the pad size?
  2. Is there a downside to running that trace below the capacitor?
  3. The datasheet allows up to 2A on the output side, however I'd presume I need to account for more on the LXn traces (i.e. the FET output). How much more?

Last, if there is a glaring error in the design that immediately jumps at you, I'd like to know.

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  • \$\begingroup\$ You can try putting a plane on your top layer so your ground connections can just be thermals instead of single traces to single vias. What's your copper to drill clearance setting? It may be larger than it needs to be which is probably causing you to be wary of adding more vias. You can add more vias and move the components closer which would allow you to reduce a lot of those signal loops. \$\endgroup\$ – scld Nov 14 '14 at 13:00
  • \$\begingroup\$ @scld, that doesn't appear to make much difference. The thermals generated are marginally wider than the traces. \$\endgroup\$ – Simon Richter Nov 14 '14 at 13:39
  • \$\begingroup\$ I would certainly identify and increase trace widths of any traces carrying 2A. \$\endgroup\$ – Brian Drummond Nov 14 '14 at 14:16
  • \$\begingroup\$ @BrianDrummond, my suspicion is that I can only adjust copper thickness here, as the pad size is given. \$\endgroup\$ – Simon Richter Nov 14 '14 at 14:24
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    \$\begingroup\$ You can keep the narrow sections of track (pads, traces between 0603 pads if you can't reroute them) as short as possible, and widen everything else. \$\endgroup\$ – Brian Drummond Nov 14 '14 at 14:27

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