For one of my current projects, I am designing a small data acquisition board. However, I am currently not sure about the overall layout of the board.
My question is actually regarding the position of the I2C expander and its position. The LED's it drives have to be in this position for visibility. The I2C expander has to be powered by the digital supply. The state of the LED's will not change during data acquisition and also the I2C bus will not have to transmit any data during the acquisition.
So here are my questions:
- which of the 2 layouts is better in terms of EMI / radiated emissions?
- For the case, that the LED state does not change during acquisition, do I have to expect any other negative effects on the ADC due to the constant LED currents / I2C expander quiescent currents?
- If 1 and 2 are both not optimal, what have I missed and how could I arrange it better?
- For case 2, would it be better to have the GND left unconnected on 1 side of creating a loop with the analog plane in the middle?
The MCU I'm planning to use is an STM32F103 - Product page