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The common mode choke serves as a protective measure against potential ESC and environmental EMI common mode noises. Typically, it functions as a short, connecting the battery and the buck converter input. The power FETs of the ESC constantly alternate between the battery's power and ground, causing ringing at both VBAT and ground, known as common mode noise. Since the servo module draws power from the same battery, the noise has the potential to be transferred to the buck converter's input. Ideally, the ESC addresses its FET ringing issue on the PCB. We added common mode choke for an extra layer of noise protectionmitigation.
How does the common mode choke work?
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https://electronics.stackexchange.com/questions/630389/why-does-the-signal-and-power-supply-in-my-custom-esc-breadboard-become-so-noisy https://electronics.stackexchange.com/questions/53914/ground-noise-and-voltage-drop-problem
https://electronics.stackexchange.com/questions/79752/what-is-common-mode-noise
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The SBD will clamp the output voltage at -0.28V for chip protection since the datasheet specified the absolute minimum Vout is -0.3V. It will be placed for the 1st revision just in case if things go wrong.
PWM Buffer Component Selection
Requirement
4-channel
Vin >= 6V
Can buff 3.3V PWM https://docs.holybro.com/autopilot/pixhawk-baseboards/pixhawk-baseboard-ports
Selected SN74HC125PWR for cheap price and small package
Input Pulldown Resistors
I couldn’t find our flight controller (Pixhawk 6) PWM rail leakage current. Selected 4.7k as pulldown resistor value.
PCB Layout Notes
Layout Topology
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