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xtr117 - DGND-AGND

juan camarasa
Intellectual 390 points

Other Parts Discussed in Thread: MSP430F2274, XTR117

I designed the following circuit and I am in doubt if I need to generate 2 ground planes connected to DGND and AGND or  I can use a single ground plane.
Currently I have armed the system with a single ground plane and it works.

I was wondering what is the  best  approach to the GND tree issue to eliminate interference caused by mixed analog-digital GND current.

I have connected the xtr117 with the msp430f2274

  • 0
    Guru 21975 points

    Juan,

    It is not possible to provide a definite answer to your question. Given that you apparently have a working system and have not detected specific issues, it would seem that a single ground plane would be adequate.

    In general, I believe it would be good to order the grounding connections so that analog input grounding is closest to the Iret pin of the XTR117. MSP430 grounding would be further down the line. The digital power supply to the MSP430 should have a bypass capacitor located close to the supply pin connection and it should return to a ground connection that has a direct ground plane connection to the digital ground of the MSP430.

    Without more detail of how the analog input to the XTR117 is developed it is not possible to give much more advice than this.

    I see that you have selected a 2N2222 transistor for Q1. Be aware that Q1 must dissipate substantial power at full-scale output current and the thermal resistance of the 2N2222 is quite high. I recommend using a transistor with some type of thermal tab mounting for good thermal dissipation characteristics. The data sheet provides some recommendations. The electrical characteristics of this transistor are not particularly critical and there are many possible choices.

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    Intellectual 390 points

    Bruce,

    thank you very much for your recommendations.

    Regards, Juan