<aside> <img src="/icons/warning_lightgray.svg" alt="/icons/warning_lightgray.svg" width="40px" />
WARNING: Oversimplified information is contained in here! Use external resources to complete your understanding of schematic and layout theory.
</aside>
When drawing, every circuit in your device needs to be closed, deliberately left unconnected, or switchable. Often, closing a circuit means connecting it to ground (GND).
Ground is just the conductive conduit of lowest potential in your electronic circuit.
Example schematic diagram of a DC-to-DC converter in Altium Designer.
You can see the big yellow ‘box’ in the centre of the screen- in this case, it represents a PMU8218 IC/module. It has 24 pinouts, each of which are labelled for their purpose (and as they are shown in the datasheet). You can see its various analog ground (AGND) and power ground (PGND) sections, as well as a resistor divider on the feedback (FB) pin. These features make this chip likely to be some form of a DC-to-DC converter.
<aside> 💡
https://learn.sparkfun.com/tutorials/voltage-dividers/all
https://youtu.be/19WnYPhNOH0?si=oKfozdgshNhNSqtS
</aside>
In many cases, the datasheet for an IC will come with a “Recommended Application Design” or similar. It’s a good idea to understand and copy the design for yourself, modified appropriately for your specific system requirements. Sometimes they even come with recommended physical layouts (often for complex MCUs with WiFi/RF, antenna modules, or sensitive power converters).
While this will be further explained in later sections, every red-orange label here (e.g. 8V, GND, AGND, 3V8, 3V8LO) is a net label. We use them to clearly define each “net”, or section of the circuit. You can name them whatever you want.
They are somewhat self-explanatory - in the above image for example, everything connected to the 8V net label (the “power rail”) is going to be connected with each other. You can assume there’s a connector off-screen that is connected to the 8V rail, which is supposed to deliver the source voltage.
IMPORTANT CONCEPT: While LDOs (and some other devices) convert DC, they often receive noisy and unreliable DC voltage, making it so that this DC voltage could actually be considered an AC voltage (at a smaller scale). This is suboptimal, and puts your chips at risk, especially if your transient voltage spikes exceed the rated absolute maximum voltage of your ICs.
To combat this issue, a linear dropout regulator will require a set of input capacitors and output capacitors (as you’ll see in your selected LDO’s datasheet). These decoupling capacitors need to be tightly coupled (kept close) with the rest of your system, as they are directly filtering power. These will need to be connected in parallel with your main power rail (as can be seen in the example schematic above).
https://en.wikipedia.org/wiki/Decoupling_capacitor
https://learn.sparkfun.com/tutorials/capacitors/application-examples
$$ X_C = \frac{1}{2\pi fC} $$
Where X is the capacitive reactance in ohms (Ω), f is the frequency of the alternating current in Hz, and C is capacitance of the capacitor in farads (F).
Decoupling capacitors do a few things, and using the equation above, we can make a few mental connections to what happens in our circuit. You can see that C (capacitance) in most cases will be a fixed value, while the magnitude of f (frequency) largely dictates the magnitude of Xc (capacitive reactance).