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PGA411-Q1: Sin/Cos noise problem

Mert Sahin
Prodigy 150 points
Part Number: PGA411-Q1
Other Parts Discussed in Thread: TMS320F28335

Dear Clancy,

In our motor control project we use resolver sensor. In prototype A we encounter no problem after reaching 3000 rpm. The phase currents were really fine. Position feedback also had no problem.

Below please find the schematic of prototype A.

In prototype B, the problem starts when we increase speed. We tried to monitor IZ2 and IZ4 when motoring.

At zero speed. (Yellow: AOUT pin, Blue: IZ2-IZ4 with differential voltage probe)

At 200 rpm.

At 1000 rpm below.

At 3000 rpm.

And the schematic of prototype B is below.

What could be the cause of this increasing noise on sine or cosine interface? Could you help us sort this out? This noise also jeopardize phase current. Waveform of phase current is affected seriouly. 

Thanks a lot in advance.

Mert

  • 0
    TI__Mastermind 23810 points

    Mert,

    The AFE filtering has not significantly changed between the two boards, so something else must be the problem. Did anything change in the grounding scheme or the power tree between the two boards? Does this issue go away if the motor's casing is grounded?

    Finally, note that the AOUT waveform ringing might not be indicative of the actual angle output. To check you would need to log the actual angle readbacks for a few revolutions.

  • 0 in reply to Clancy Soehren
    Prodigy 150 points

    Dear Clancy,

    For the first prototype we had single ground all tied together. Power ground, Analog ground and digital ground.

    For the second, problematic prototype, we have three different grounds. Digital and analog grounds are tied at single point under TMS320F28335 dsp. Power ground is completely isolated from digital and analog grounds. We even read bus voltage isolated. 

    PGA411 in both prototypes are referenced to digital ground.

    Only significant change between these two boards is, in prototype A we supplied PGA411 I/O with 5 V. Then we needed to use level shifters to make inputs compatible to MCU. 

    Thanks a lot.

    Mert

  • 0 in reply to Mert Sahin
    TI__Mastermind 23810 points

    A change in grounding scheme is suspicious when the new board has visible noise issues. Is it possible to modify one of your new boards and connect the separate ground planes using copper tape? 

    Have you been able to identify where the noise is originating from?

  • 0 in reply to Clancy Soehren
    Prodigy 150 points

    Hello Clancy,

    Unfortunately no. 

    Do you have alternative filter suggestions for AFE. Maybe a change in common mode or differantial mode filter values.

    Thanks a lot.

    Mert

  • 0 in reply to Clancy Soehren
    TI__Genius 11015 points

    Mert,

    Clancy is out on vacation & I will help you with this issue in the meanwhile.

    To start with please try to remove the device from the board B and use that in board A and check if the noise goes out.

    Also as Clancy suggested, change in grounding schemes do account for noises and try to isolate the blocks in the circuit and identify the source of noise.

    We do not have any alternative filtering options at the moment.