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Original question:

MSP430F67791A: Purpose for EEPROM in TIDM-THDREADING design

MSP430F6779A: PZ Package Layout Review Request

dflohr
Expert 1140 points

Part Number: MSP430F6779A
Other Parts Discussed in Thread: MSP430F6779

For James Evans,

How can we get a quick layout review of our meter board implementation of MSP430F6779 based off TI reference design? Prefer to NOT post the screen shots here.  

Thanks

Dan

  • 0
    TI__Mastermind 49692 points
    Hello Dan,

    Good to hear from you! Thank you for not posting the private screenshots here in the forum. Just to let you know, Brian has been in contact with me about this request via email. I expect to have the review done in less than a week at the latest. I've got several other priorities right now, but when I can get to it, the review shouldn't take too long. I may have questions, but I'll share them via email, not here.

    Regards,

    James

    MSP Customer Applications
  • 0 in reply to James Evans
    TI__Mastermind 49692 points
    Hello Dan,

    Just to let you know, the review has been completed and feedback shared with Brian.

    Regards,

    James

    MSP Customer Applications
  • 0 in reply to James Evans
    Expert 1140 points
    James:

    Meter bare boards due in shortly. BOM kit being assembled. Few questions have arisen to make sure we get it right and try to consolidate number of unique items.

    Questions Based on Original TI 6779 Meter Reference Schematic

    1. R/L7 thru R/L14 Analog Front end CT series coupling parts. In your testing, were Inductors found to be needed or just 0 Ohm jumpers?

    2. R20 thru R23, CT burden resistors. Presume these were sized for a specific CT. Any guidance you can point to on sizing these for other CTs?

    3. Using the 32 KHz crystal in the BOM, C37 and C40 12 pF caps should not be populated. Correct?

    4. R51 and C53 are the RC on the 6779 RST Pin. How critical is R51 value? Would slowing it down a bit using 56K instead of 47K be OK?

    Thanks

    Dan
  • 0 in reply to dflohr
    TI__Mastermind 49692 points

    Hello Dan,

    dflohr said:
    Meter bare boards due in shortly. BOM kit being assembled. Few questions have arisen to make sure we get it right and try to consolidate number of unique items.

    Excellent!

    dflohr said:
    1. R/L7 thru R/L14 Analog Front end CT series coupling parts. In your testing, were Inductors found to be needed or just 0 Ohm jumpers?

    The 0 Ohm resistors are placeholders for inductors or ferrite beads in case that noise or ESD/surge protection is required. There's some good discussion around these protection devices in the following thread.

    TIDM-THREEPHASEMETER-F6779: Current font-end diode clamps? Why 2 diodes in series?

    dflohr said:
    2. R20 thru R23, CT burden resistors. Presume these were sized for a specific CT. Any guidance you can point to on sizing these for other CTs?

    Sure! Actually, our EMDC tool can help with this. For each CT placed in the EMDC workspace, you can modify the parameters to meet your requirements. For each CT, enter your absolute max IRMS value, and the CT's turn ratio. Then, you can adjust the burden resistor accordingly to use most of the Full-Scale Range (FSR). The RMS values are automatically converted to peak for easy comparison to the max ADC input value (FSR).

    dflohr said:
    3. Using the 32 KHz crystal in the BOM, C37 and C40 12 pF caps should not be populated. Correct?

    I would recommend that external load capacitors are used. They're more accurate and consistent than the internal load capacitors. Select the load capacitors based on your crystal's effective load capacitance. Refer to the MSP430 32-kHz Crystal Oscillators app note for more details.

    dflohr said:
    4. R51 and C53 are the RC on the 6779 RST Pin. How critical is R51 value? Would slowing it down a bit using 56K instead of 47K be OK?

    Use what's recommended in the datasheet. These values are important and shouldn't be changed. Again, refer to Figure 2-3 in the MSP Hardware Tools User's Guide (SLAU278). Depending on how fast SBW speed is, you may actually need a capacitor smaller than 2.2uF (maybe around 1.1nF) due to parasitic capacitance on the PCB. See the footnote at the bottom of Figure 2-3.

    Regards,

    James

    MSP Customer Applications

  • 0 in reply to James Evans
    Expert 1140 points

    James:  Thanks.

    1.   OK.  For now we'll just put in jumpers

    2.   Will track down EMDC tool

    3.   Will install the 12 pF caps as per the TI reference design schematic ( which BTW says "DNI")

    4    47K OK,    The TI Reference schematic calls out the RC cap as   C53   .1uF     not 2.2 nF  but I guess that is if you don't use SBW   will use 1.1 nF in the build

    Rgds

    Dan 

  • 0 in reply to dflohr
    TI__Mastermind 49692 points
    Sounds good!

    Regards,

    James

    MSP Customer Applications

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