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MSP432E401Y: Design confirmation in Figure 29 of System Design Guidelines for SimpleLink MSP432E4 Microcontrollers

Jonathan Geronga
Expert 7930 points
Part Number: MSP432E401Y

Hi Team,

Our customer would like to get clarifications in the section 4.1 of System Design Guidelines for SimpleLink MSP432E4 Microcontrollers document (SLAA770).

It describes the external circuitry required for the ethernet internal PHY. The diagram included in Figure 29 includes this circuitry. Connected to the part RJ45 are a resistor and capacitor (R44 and C38). From their design research, they have always seen a high rated capacitor connected between the chassis ground and MCU ground but have never seen a resistor connected in such a way, linking the different grounds. 
They are wondering if they could get some clarification or explanation on the purpose of R44 and whether it is necessary for this design.
Also, if the ground labeled "chassis" is equivalent to earth ground (third prong on an outlet). 

Thanks,

Jonathan

  • 0
    TI__Mastermind 32900 points

    1. I think it just to want DGND and chassis ground has same voltage level. I am not an expert on this part. I look into the schematic of beaglebone white. You can see it also add a R138 with 1R between DGND and chassis ground. 

    2. labeled "chassis" is equivalent to earth ground (third prong on an outlet). Because normally, we will connect the chassis to third prong on an outlet.