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Original question:

CCS/TMS320F28033: TMS320F28033

CCS/TMS320F28033: TMS320F28033

vishal sapara
Intellectual 640 points
Part Number: TMS320F28033
Other Parts Discussed in Thread: SM73201

Tool/software: Code Composer Studio

SIR,

THANKS FOR REPLY.

sir my code is working. . when i has PRESSED switch (SW1) and probed at TEST POINT (TP17) ARC is generating so it is OK.

  

but when i measure same signal after CAPACITOR (C75)  it is not transferring to ADC pin

what i have done is, i has removed this capacitor (C75) and i am sure that i has already R63 AND C78 RC filter is available on ADC pin so i would not pic up a noise.

now i did not understand why this capacitor needed to be removed.?

what happen if actual ARC is generating then i needed the this capacitor?

regards,

vishal.

  • 0
    TI__Guru* 95315 points
    Vishal,
    Your query needs to be addressed by a different team. I am working to find out the appropriate group for this.
  • 0 in reply to Hareesh Janakiraman
    TI__Mastermind 48310 points
    Hello Vishal,

    I am not familiar with the details of this reference design, but I can support the SM73201 related questions.

    The RC network made up of C75, R62, R63, and C78 form a bandpass filter. C75,R62 form the high pass portion of the response, with a -3dB frequency of 339Hz. C78 and R63 form the low pass portion of the response, with a -3dB frequency of 678kHz.

    If I interpret your scope picture above correctly, the input frequency is around 700kHz with a peak to peak amplitude of 4.24V. In this case, I would expect this to be attenuated by about 3.5dB.

    Can you measure the response with C78 installed at the ADC input, node ADC+IN? I would expect a similar waveform, but with a peak-to-peak magnitude of around 2.7V. In this case, the peak to peak value should be the same with C78 installed or with a 0ohm jumper installed since the 'noise' frequency of 700kHz is much higher than the HP cutoff frequency of 339Hz.

    Also, looking at the reference schematic on page 7, there is a note stating that the power supply for the board, +V, needs to be between 8V and 12V for proper operation of ARC noise circuit. If you are operating with a supply voltage of less than 8V, this may explain why the system does not detect the test 'noise' waveform.

    Regards,
    Keith N.
    Precision ADC Applications
  • 0 in reply to Keith Nicholas
    Intellectual 640 points
    dear sir,
    thanks for replay.
    but frequency in my scope is around 100khz if you check that 50uS is timing and 10us is 1-dots so it is 100khz.
    and as band pass filter is around frequency is around 339hz to 678khz. so my frequency must be pass by BPF. And also HPF cutoff is of 339HZ which is form by c75 and r62. so it has to be passed by HPF also as input signal is of 100khz without any attenuation. and also i has given 10v supply so arc circuit. so why i need to remove C75.
    regards,
    vishal.
  • 0 in reply to vishal sapara
    TI__Mastermind 48310 points
    Hello Vishal,

    I misinterpreted your scope capture. O.K., so the frequency is closer to 100kHz. I agree this should pass through the HP section of the filter with little or no attenuation.

    When you remove C75, do you replace it with a short, or 0ohm jumper? With C75 in the circuit, do you measure the same waveform, frequency and amplitude, directly on pin 2 of the SM73201 ADC? Have you tried replacing C75 with a different 0.047uF capacitor to make sure the capacitor is not damaged?

    There is already quite a bit of filtering before the ARC signal gets to C75. The only reason that I can see for this capacitor is to block DC offset voltages, and then establish a new DC bias level of 2.5V through R62.

    Regards,
    Keith
  • 0 in reply to Keith Nicholas
    Intellectual 640 points
    Thank you sir,
    Sir I has replaced C75 with short circuit... Not by zero ohm because I want to check whether it is working or not..
    When I has measure signal at BEFORE C75 when it was mounted , same signal I am able to see after removing C75 capacitor On this pin. So I has removed it.
    So can I remove it from my circuit?
  • 0 in reply to vishal sapara
    TI__Mastermind 48310 points
    Hello Vishal,

    I cannot say 100% how this will effect the overall system performance, but you should be O.K. removing C75 and replace with a short circuit. C75 forms a high pass filter, but there are already multiple high pass filter stages in the design. You will get some additional signal content below 375Hz. This may result in the ADC input saturating for certain signals, but this depends on the overall frequency content of the ARC. I think the firmware will 'filter' this out, so as long as the additional bandwidth does not saturate the ADC input, then there should be very little difference in the overall performance.

    Regards,
    Keith N.