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I've read following valuable article: 'TI Designs: TIDA-01630 High EMC Immunity RS485 Interface Reference Design for Tamagawa Encoders'. 

However, I could not find whether 'Earth' (plane under SubD-15 female connector) was connected to GND via R1 and C1 during  IEC-61000-4-4 Electrical Fast Transient (EFT) test (shown with figure 18). I realize (figure 19) that TIDA-01630 connector was bonded to metal (RF) plate during test, but would like to know what was the case with R1 and C1 - have they been used (placed on pcb) or not?

If not, how was then circuit GND connected to metal plate ('Earth')?

If yes, how that affect function of C12 and C15 (figure 3) or C19 and C 22 used to further improve  immunity to CM disturbances? 

Thank you,


  • Hello Svebor,

    thank you for your interest in TIDA-01630 and pointing out the Earth to logic GND connection. We used R1 = 10MOhm to connect the encoder shield (Earth) to the logic GND.

    I realize the schematics and design guide is not correct here and we will update the schematics with R1=10MOhm accordingly. In the design guide we also need to change the comment on the pulse proof resistors, which we set to 0 Ohm. Please expect an update in a few weeks.

    On that TI design and EMC immunity test, we didn't populate C12 and C15 as indicated. So all tests where done as outlined in the schematics except for that R1=10Mohm was populated.

    We've done Initial internal EFT tests with either C12 and C15 decoupling versus a center placed single capacitor (C16). We tested this setup with our TI design on both ends, hence no Tamagawa encoder. With that configuration, it looks like C16 offers slightly better common mode rejection, likely due to slight mismatch of C12 and C15 due to tolerances.

    Martin Staebler
    Texas Instruments
  • In reply to Martin Staebler:

    I appreciate your fast and detailed answer on this. Thank you,
    Svebor Tomasović