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TIDM-1PHMTR-ESD: current/voltage front ends

Part Number: TIDM-1PHMTR-ESD
Other Parts Discussed in Thread: TIDM-3PHMTR-TAMP-ESD, , TVS0500, MSP430F67791A

Hello,

with regard to the emi filter at both voltage and current front end, if I rightly understood, this is only a differential mode filter (no common mode filter) consisting of L1, L2 and C27 ? why is C27 located near to the IC, is it to decrease the loop area?

It is mentioned that a lower value resistor is used for the anti-alias filte at the positive terminal, however, in a similar design TIDM-3PHMTR-TAMP-ESD, the same sentence is mentioned but still R18 and R34 the same value at 100K, would you please check it?

If I rightly understood, no TVS is used with the voltage input  but a MOV to save cost?

Is there please some Tool available by TI to help design the EMI filters?

Regards,

Amr

  • Amr,

    L1 and L2 are used for EMI suppression. C27, on the other hand, is part of the anti-alias filter.

    You are correct in that the TIDM-3PHMTR-TAMP-ESD design uses a 1k Ohm resistor instead of the 100 Ohm resistor in the voltage front-end for TIDM-1PHMTR-ESD.  The change in resistance values would cause an additional phase shift, which would get canceled out after performing phase compensation on the meter.  

    For the voltage front-end, we used a varistor on the voltage input instead of a TVS device.  We do have a TVS diode though in the current circuit.  The TVS diodes used in the design are older parts.  For later designs, we replaced these older TVS devices with a couple of TVS0500 devices.   

    We do not have a tool for simulating this exact circuit, but the response of the passives in this circuit can be simulated using TINA

    Regards,

    Mekre

  • Hi Mekre,

    thank you very much for the info.

    for selection of the TVS, may I ask you please if you selected it based on a surge specification(within 20us) or based on an esd specification (within 100ns). 

    How to get the TLP corresponding to the IEC61000-4-2 of the used microcontroller? the given ESD ratings of the microcontroller are HBM or CDM only. 

    In the attached figure, what is the purpose of the diodes circled with red Color?

    Regards,

    Amr

  • Amr,

    The TVS diode is more for surge protection and the diodes are more for ESD protection.

    I will check internally if we have the TLP model for the MSP430F67791A and then get back to you.

    Regards,
    Mekre

  • Hello Mekre,

    according to the datasheet of the TVS diode, it shows it is rated for the ICE 61000-4-2 for ESD. The datasheet seems not to mention anything about the surge but only  400W Peak pulse power capability at 10/1000µs (which might be something similar to the IEC61643-321 for surges) I'm not sure.

    May I ask you please why to use extra diodes for ESD although the TVS seems to already suffice the requirements of ESD?

    Does Ti have some tutorial on the diodes highlighted in my last message (not the TVS)?

    Regards,
    Amr

  • Amr,

    I was able to check internally on your TLP question.  We unfortunately do not have any TLP data for the MSP430F67791A specifically.

    In regards to the diodes, these diodes were used as an additional precaution to make sure that the voltages fed to the MSP430 sigma delta pins don't go outside the absolute input voltage of these pins, which is from AVSS-1  to AVCC Volts.

    Regards,

    Mekre 

  • Hello Mekre,

    thank you very much for your feedback.

    Regards,

    Amr

  • Hello Mekre,

    I have checked the single line diagram of the meter and can't get very well what is the voltage being measured between V1+ and V1-. The voltage divider seems measuring the voltage of L(N) but the ground point seems not clear. The ground is connected to the secondary of the CT. Could you please give some hint on that?

    Kind Regards,

    Amr

  • Amr,

    The voltage between V1+ and V1- in Figure 6 of the design document is a divided down version of the Mains voltage, which is applied between the board's "Line" and "Neutral" pads.  In this circuit, the "Neutral" pad on the design is connected to the board's GND.

    Regards,

    Mekre

  • Hi Mekre,

    thanks very much. 

    I would like to make sure of somethings please. In the following figure, if I rightly understood, in the following figure, the red and the green traces are for surges from the CT side.

    While in the following figure, the traces 1 and 2 are from surges that can affect the AVCC, GND pins.

    - the previous circuit considers CT's with 1A rated current. What is one would use a 5A rated secondary current? I believe one can use the same surge/ESD protectors in the previous figures but only make sure that the voltage across the burden resistor would not cause operation of any of the TVS diodes at normal system operating conditions. May you please confirm that?

    - again in the block diagram of the meter system, shown below, one can say that points W, y and Z are the same point considering the Rsense is a very low resistance.

    Kind Regards,

    Amr Elhadidy

  • Amr,

    The diodes are for clamping the analog input pins so that they are within the absolute voltage range of these pins.  Instead of the 1-diode arrangement shown in your last post, it would be better to use the 2-diode implementation you showed in your post from May 27th.  The 2-diode implementation has a higher clamping voltage, which would prevent premature voltage clamping at higher currents.

    In regards to your second point, could you verify which block diagram you are referring to? 

    Thank you,

    Mekre

  • Hi Mekre,

    sorry I forgot to attach the connection diagram in the last post.

    In your previous post you mentioned it is much better to use the 2-diode implementation with higher currents: By higher currents, do you mean the 5A CT?

    Regards,

    Amr

  • Amr,

    Yes, points X, Y, and Z are at roughly around the same voltage.  Technically, there is a voltage drop between points X and Y because of the voltage drop across the shunts; however, this voltage is relatively small when you compare it to the voltage between line and neutral.

    Regards,

    Mekre

  • Hello Mekre,

    thanks very much for your feedback.

    Kind Regards,

    Amr