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Original question:

DRV8329-Q1: DRV8329-Q1: Regarding the EMC CE02 issue:

DRV8329-Q1: The issue with the 95M frequency point

user6354551
Prodigy 230 points
Part Number: DRV8329-Q1
Other Parts Discussed in Thread: DRV8329

Tool/software:

Hello!
After removing the pump capacitor on our side, we found that there was no attenuation at the 95M frequency.
Using the near-field antenna of a spectrum analyzer to scan the DRV8329 chip and its vicinity, strong radiation frequencies were received. Could you please explain how this frequency is generated by the chip and what solutions are available? It seems like the chip itself is emitting these frequencies.

 

  • 0
    TI__Prodigy 335 points

    Hello!

    Thank you for your question. I am examining your query and will aim to get to you by the end of the week.

    Cheers,

    Joel A. Adejola

  • 0
    TI__Prodigy 335 points

    Hello! Thank you for your patience. None of the parts in our device operate at that frequency. So, I have some questions (and tests) that would help us to figure out where this spike radiation stems from.

    - What were the other conditions around the test you conducted?

    - If the device is in SLEEP mode, do you observe any readings?

    - If your configuration allows you to, remove the 1uF ceramic capacitor between AVDD and AGND to see and conduct the same test.

    - Otherwise, could I kindly see your current AVDD-AGND-capacitor placement and routing?

    Cheers,

    Joel A. Adejola

  • 0 in reply to Joel A. Adejola
    Prodigy 230 points

    Hello, the test condition is that when the SLEEP pin is pulled high, the motor does not rotate.
    After SLEEP is pulled down, the frequency point disappears.
    We conducted a full-band frequency sweep here and discovered the following frequency points:
    31.77MHz, 63.5MHz, 79.4MHz, 95.3MHz, 127MHz.
    95MHz should be tripled in frequency. Switching to another chip may introduce slight errors.
    Please help confirm whether the DRV8329 has an internal frequency of around 31.7MHz and the corresponding solutions.

    After removing the 1uF capacitor, the frequency point still exists.

  • 0 in reply to user6354551
    TI__Prodigy 335 points

    Thank you for running the tests and the extra information. We are having a look and will revert to you imminently.

    Cheers,

    Joel A. Adejola!

  • 0
    TI__Prodigy 335 points

    Hello - It does appear as though these frequencies are harmonics coming from our device and is related to circuitry on AVDD. Minimizing the inductance in the ground loop between the AGND pin and C_AVDD should help reduce the magnitude of the observed frequencies.

     

    Cheers,

    Joel A. A.