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PGA970EVM: Distorted primary waveform output

Paul Kruchko
Prodigy 140 points

Part Number: PGA970EVM

Hello,

We have had some issues trying to drive the primary side of an RVDT, with a primary coil resistance and inductance of 42 Ohms, 7.27mH, and a secondary resistance and inductance of 33 Ohms and 9 mH.

As can be seen below, we are generating a clean 3kHz, 16Vpp sine wave when unloaded; however, when we connect the primary and secondary connections to the RVDT the waveform becomes heavily distorted. We originally thought that if we populated the push-pull amplified section that it would improve the drive characteristics, but unfortunately it did not. Any suggestions on what the issue might be?

Unloaded

Loaded with the previously described RVDT.

  • 0
    TI__Mastermind 31655 points
    Hi Paul,

    Can you please provide the waveform settings that you are using to generate the primary drive? A screencapture of the GUI settings under the waveform generation section is fine.

    Are there any additional components between the waveform output and your RVDT?

    Regards,
  • 0 in reply to Scott Cummins
    Prodigy 140 points

    Hi Scott,

    We figured it out, we are getting a nice clean sine wave out now. After populating the push-pull amplifier region to get the full class D amplifier experience, we forgot to de-pop the 0 ohm resistors that were being used in the eval board to bypass the push-pull output stage (R72 and R67 on the EVM user guide's schematic.) I really wish the user guide was more explicit about populating the push-pull stage and de-popping the zero ohm resistors when connecting an inductive load to the eval module. Is there a way to submit a request to TI to have them update the literature (SLDU017) to be more explicit about the external amplifier stage configuration? We destroyed a couple boards now, not knowing better from the beginning.

  • 0 in reply to Paul Kruchko
    TI__Mastermind 31655 points

    Hi Paul,

    Thanks for the feedback. I'll make sure that gets updated to be explicitly mentioned in the documentation. Glad you got it figured out!

    Regards,