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OPA365: OPA365: Analog Pulse Width Modulation

Paul Ren
Prodigy 640 points
Part Number: OPA365

Hello,

My customer has adopted our recommended analog pulse width modulation as the following link:

www.ti.com/.../slau508.pdf

However, they found their circuit is easily interfered by 300MHz~400MHz RF emission, even the circuit has been shielded with metal case.

Is there any suggestion to improve the circuit immunity to such RF signal?

Additionally, could you suggest the way to enhance the PWM accuracy?

B.R

Paul

  • 0
    Guru 140200 points

    Hi Paul,

    the circuit can be made more immune to such frequencies by adding some suitable low pass filtering. Where is the circuit interfered, at the input or output?

    Where and how are you using this circuit? Can you show a block diagramm? This decides where and how to put the filter(s) :-)

    Kai

  • 0 in reply to kai klaas69
    TI__Prodigy 640 points

    Hi Kai,

    Please note the schematic for PWM generator.

    As they are using RF signal to interfere this circuit, they don`t know where interference injects.

    We try to increase the value of R20/R22/R32 to 10Ku, but the accuracy drifts with temperature change.

    Please suggest how the filter can be added? We can try it on the board.

    If you left you email, I can send the full schematic to you. Thanks!

    B.R

    Paul 

  • 0 in reply to Paul Ren
    TI__Genius 15555 points

    Hello Paul,

    It is difficult to determine where the filter should be added without knowing where this is causing issues in you circuit. Waveforms will need to be captured at various points while RF signal is affecting the board.

    Best,

    Hasan Babiker

  • 0 in reply to Hasan Babiker31
    TI__Prodigy 640 points

    Hi Hasan,

    Could you suggest any points we can capture the waveform?

    This case is pretty urgent, can we discuss it through email? So that I can send you the full customer schematic and other material to facilitate customer issue.

    B.R

    Paul

  • 0 in reply to Paul Ren
    TI__Genius 15555 points

    Hello Paul, 

    Yes, feel free to contact me outside of the forums to resolve this issue.

    Best,

    Hasan Babiker