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TIDM-1PHMTR-ESD: A question about the ground plane

moshe jacobson18
Expert 2090 points
Part Number: TIDM-1PHMTR-ESD

Hi anyone

This may be a basic question...but...

In the design for the TIDM-1PHMTR the power to the board is from supply live and supply neutral to an R-C voltage reducing and rectifying circuit ending at an TPS77001.

Supply neutral forms the -ve/ground plane for the board.

The connections for SDB24s (to V1+ & V1-, and I+/I-) on the MSP430 come from supply live with the part of the circuit terminating on -ve (which is neutral).
Internal to the SDB24 is the MSP430 -ve circuit.

So now my question:

If I were to create an EVM whose power supply to the board (and by extension to the MSP430) instead of the above solution, were to come from an external 12V DC supply (ie the power reduction R-C circuit of the TIDM-1PHMTR is removed entirely).
What effect will that have on the SDB24s (& the values they generate) as those circuits are still between supply live and supply neutral (and of course supply neutral is now not connected to the new -ve of the board)?


thanks in advance

  • 0
    TI__Mastermind 49692 points

    Hello Moshe,

    Thank you for your question. I'll do my best to explain it simply.

    First, the TIDM-1PHMTR-ESD EVM allows two different power supplies to be used (obviously not at the same time). Jumper JP4 allows you to select the source for supplying DVCC (highlighted in the screenshot below) from either the on-board RC-based power supply (jumper on the VCC_PL side of JP4) or an external power supply (jumper on the VCC_EXT side of JP4). Header JP3 (notice this isn't a jumper because the two pins are voltage and ground) allows you to supply 3.3VDC and ground to the VCC_EXT and GND pins of JP3 respectively. You can read more about this in the User's Guide.

    Basically, there are two different ground planes on this EVM:

    • DGND (digital ground)
    • AGND (analog ground)

    The GND pin of the JP3 header connects primarily to the DGND plane (highlighted in the screenshot below). However, you'll notice that it's also connected to R22, which is a zero-ohm resistor that connects DGND to Neutral.

    Now, Neutral is also connected to AGND plane (highlighted in the screenshot below) through the inductor L2.

    If you were to change this design, I'd recommend implementing these connections at JP3 in the same way substituting the pins of JP3 with your 3.3VDC output voltage and ground traces. R22 is the only point that connects the DGND plane to the AGND plane directly, which helps reduce noise.

    Lastly, you asked how this power supply would impact the results of the SD24 module. Well, if you change the power supply, you'll just have to go through the calibration procedure again. For example, if you change JP4 and power supply on the EVM, you'd have to re-calibrate it. Basically, the supply voltages will differ enough where the change on the internal reference voltage would create different results for the same High Voltage (HV) inputs.

    Does all this make sense?

    Regards,

    James

    MSP Customer Applications

  • 0 in reply to James Evans
    Expert 2090 points
    James....yes...thank you for that.
    But the one part of the question still needs to be resolved....is the fact that the voltage reference on either side of the SDB24 (internal vs external) completely academic?
  • 0 in reply to moshe jacobson18
    TI__Mastermind 49692 points

    moshe jacobson18 said:
    the voltage reference on either side of the SDB24 (internal vs external)

    I'm not sure what you mean. Are you referring to an actual voltage reference for the SD24 module or referencing ground to Neutral or Line?

    Regards,

    James

    MSP Customer Applications

  • 0 in reply to James Evans
    Expert 2090 points

    i meant in the case where the digital part of the board is supplied from a separate external source:
    So given an input connection (to the SDB24) that is at 220V with respect to its AGND and a SDB24 port that is at 3.3V with respect to its -ve; is there any concern (or comment) about the issue of the 2 ground planes being completely different in both character & voltage affecting the port in any way?

    And of course not forgetting that whilst the 2 ground planes are not connected to each other the other planes (live supply & +ve) DO have an interaction IN the port.

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