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I'm designing my first PCB and probably the circuit is a bit complex for my electronics knowledge. So a doubt arised while drawing the layout.

The board has got a Microchip MCP73871, an integrated circuit that manages the charge of lithium batteries with solar power. If there is a load while the battery is charging, the MCP73871 sends the power needed to a step-up/step down voltage regulator IC Texas Instruments TPS63060 to regulate the voltage to 5V in order to power an AtMega328P.

So speaking with voltages, we have:

  • MCP73871 powered with 6V (from solar panel)
  • TPS63060 may receive 3.3-6V and outputs 5V
  • Arduino works with 5V

The question is, should I separate grounds and ground planes? Schematic

Nic1337
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2 Answers2

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No. There are very few instances in which separate grounds are necessary or good. In this case, you don't even have a mixed-signal system. There's no reason to have split ground planes, and separate grounds will only make things worse.

Take care to manage your return currents and keep the buck/boost regulator layout compact. Everything else appears to be low-frequency digital or power, so there shouldn't be any signal integrity weirdness.

uint128_t
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Separating ground based on different voltages isn't really the right way to think of it. You in essence do different grounds based on isolating noise. If you have analog and digital, you do an analog ground and digital ground to isolate the noise in a sensitive analog circuit.

A common method of laying out ground planes is to do a star connection wherein you put a localized ground under your IC and then only connect the grounds at one point. This keeps the specialized ground isolated from the rest of the ground and whatever noise may be present.

So back to your circuit. Nothing in here is extremely noisy, although your regulator may be. So keep the regulator away from anything sensitive and you'll be alright. Adding more ground planes will just create unnecessary voltage drops or strange ground return currents if planes start to couple, etc. Instead, I suggest you keep one ground plane and look into star grounding to mitigate noise.

mcmiln
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  • You don't want to do what you just described, actually, in the normal case -- localizing noise is best done by localizing the current loops so they can't couple to each other -- the return currents in the plane/grid are "guided" by the location of the traces they are returning. – ThreePhaseEel Feb 02 '16 at 01:28
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    @ThreePhaseEel This is what I'm describing. I agree that the return path can increase with a separated ground, but if you are careful with placement you are just minimizing noise under the IC. This is a very common practice which works well. I do agree I may have wanted o put a warning against causing ground loops with the star pattern. – mcmiln Feb 02 '16 at 04:13