I'm trying to design an MCU prototyping board. I have two voltage regulators (3.3 and 5V) and motor driver on my board. All grounds are common, VDD of MCU comes from 3.3V reg and power supply for motor driver module from 5V reg. The current flow from 5V reg can reach up to 2 A (most consumption from motors on driver). Plus servos and other devices can be attached to my board as required. The question is if its wrong or dangerous and what kind of security tactics do I have to take?
Electronic – Is using same ground and VDD for MCU and motor driver module safe
ground
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Best Answer
It's not wrong or dangerous, but you do have to be mindful of where the ground currents are flowing. Remember that your "ground" wire or PCB trace is not a superconductor, but rather a very small resistor. When you have 2A flowing through this, it can lead to a significant change in voltage (think of Ohm's law: voltage = current * resistance). If your motor controller is using PWM to control the motor speed, then there will be 2A in the ground trace one moment, then 0A the next, and this changing voltage drop can show up as noise to your MCU depending on where it and its voltage regulator are placed.
I answered a similar question recently with some more specific advice.