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MSP430F67751: System ground recommendations

frank bor
Prodigy 70 points
Part Number: MSP430F67751
Other Parts Discussed in Thread: TIDM-3PHMTR-TAMP-ESD, , TIDM-AUX-MODULE

Hi, I'm new to the Forum, I've recently been responsible for the realization of the Layouts. Looking at the work done by the engineers who preceded me, they used a star ground to connect GND (power connector); AGND and DGND. In the specific case of uController MSP430F67751. Pin 18 (AVSS) to AGND; pin 76 (VDSS) to DGND, up to here everything is OK, pin10 (AVSS 2) to GND (power connector). The center of the star is close and connected to pin 10. What do you think, right this way or maybe connect pin 10 to AGND and then connect the star center to the GND power connector.

  • 0
    TI__Mastermind 49692 points

    Hello Frank,

    I would recommend that Pin 10 (AVSS2) gets connected to AGND. It may be better to move the star further away from the device and have it located closer to the power connector. Please reference our Three-Phase Metrology With Enhanced ESD Protection and Tamper Detection reference design (TIDM-3PHMTR-TAMP-ESD) using our EVM430-F6779. The analog and digital grounds are separate and are connected together using 0 ohms resistors in case inductors or ferrite beads are needed between them. According to the designers, splitting the planes didn't achieve much if any accuracy improvement over a single ground plane. Here are a few references that you may find helpful.

    Grounding in mixed-signal systems demystified, Part 1

    Grounding in mixed-signal systems demystified, Part 2

    Also, please go through the MSP430F67751 datasheet (specifically Table 4 or Table 5 depending on the selected device package, reference the important footnotes below these Tables as well) and understand how the unused connections should be configured, the recommended capacitances for the power/core/reference pins, and other important connections. For example, it's very important that:

    • It is recommended to short unused analog input pairs and connect them to analog ground.
    • The pins VDSYS1 and VDSYS2 must be connected externally on board for proper device operation.
    • VCORE is for internal use only. No external current loading is possible. VCORE should only be connected to the recommended capacitor value, CVCORE.
    • LCDCAP/R33 pin must be connected to DVSS if not used.

    I hope this helps!

    Regards,

    James

    MSP Customer Applications

  • 0
    TI__Mastermind 49692 points

    As a follow-up, I would also highly recommend switching from the MSP430F67751 to the recommended replacement MSP430F67751A device. They are pin-to-pin compatible, but the A-version (keep in mind it's not the Revision here) has better ESD performance and has several errata fixed. For more details, please read through the Differences Between MSP430F67xx and MSP430F67xxA Devices app note.

    Also, please read through the User's Guide for our Battery Management and Auxiliary Power Supply Options for E-Meters (TIDM-AUX-MODULE) reference design. The AUX modules can be tricky to configure properly, so this is an excellent reference with many different examples and configurations to match your design.

    Regards,

    James

    MSP Customer Applications

  • 0 in reply to James Evans
    Prodigy 70 points
    Thank you Mr Evans, the information you gave me was clear and comprehensive. I have reviewed the documentation and agree with your observations. Regarding the version of the MSP430F67751 our company currently uses version A.

    Thank you for your suggestions, best regards.

    Frank.

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