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, 06-05-2026, 08:03 PM

I was researching into designing a macropad with CH552 and came across this repo where someone has already done it and looked at the schematic
https://github.com/wagiminator/CH552-MacroPad-plus

But I don't get why the person added so many extra decoupling capacitors that are scattered around the board, what is the purpose?

, 06-05-2026, 08:13 PM

🤖 In the meantime, here’s a response from the [FEDEVEL AI HW Assistant]().
It helps to find relevant resources for your question, but it may make mistakes as it’s still in early development.

This is the response from the AI Assistant:
Decoupling capacitors serve two primary purposes in designs like this CH552 macropad:

1. **Local Charge Reservoirs**: Each capacitor acts as a temporary energy source for nearby components. When digital ICs switch states, they create sudden current spikes (dI/dt). Capacitors placed close to power pins provide instant charge, preventing voltage droop that could cause logic errors or resets. As Eric Bogatin demonstrates, even a 1µF capacitor placed close to a switching MOSFET can outperform a larger capacitor farther away due to lower loop inductance ([Video Link](https://www.youtube.com/watch?v=ARwBwHZESOY&t=2486)).

2. **Frequency Coverage**: While modern surface-mount capacitors (like 0402) have wide frequency response, scattering multiple capacitors helps:
- Lower overall PDN (Power Distribution Network) impedance through parallel connections
- Compensate for different current demands across the board
- Counteract board-level inductance from traces/vias ([Video Link](https://www.youtube.com/watch?v=XumNc480qYo&t=1176))

In your specific case:
- The CH552 has multiple power pins (VCC, AVCC, USBVCC) - each needs local decoupling
- LEDs and switches create additional current spikes
- USB interface requires clean power for signal integrity
- Scattering helps create a low-impedance power plane across the entire board

Key insight from hardware experts: With modern SMD capacitors, **placement and quantity often matter more than specific values**.

, 06-05-2026, 08:13 PM

Ten 0.1µF caps strategically placed typically outperform one perfect 1µF cap due to distributed inductance reduction ([Video Link](https://www.youtube.com/watch?v=ARwBwHZESOY&t=3822)).

You can continue chatting with the AI Assistant here:
https://fedevel.com/hw-assistant

QDrives , 06-07-2026, 02:29 PM

The MCU has a single power supply input. So a single decoupling capacitor can be sufficient.

, 06-08-2026, 03:56 AM

that does not answer my question?

QDrives , 06-08-2026, 12:48 PM

Then you should ask the original designer why he did it.
It is not a question why you *need* it, as you do not need it.

Robert Feranec , 06-09-2026, 02:11 PM

maybe they supposed to help with decoupling of the addressable LEDs?

QDrives , 06-09-2026, 07:26 PM

Good point. I just looked at the PCB photo, simple schematic and MCU datasheet.