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TMS320F280037: steady state error in frequency calculation using ADC peripheral.

Mahendra Gupta
Prodigy 45 points

Part Number: TMS320F280037
Other Parts Discussed in Thread: TMS320F28379D,

Hi,

My application is Online Industrial UPS.

Earlier i was working with the TMS320F28379d, in which my frequency calculation(50Hz) is correct using ADC signal as well as software generated signal using PLL.

But Now i migrated to TMS320F280037, I am facing issue in frequency calculation(49.62Hz) using same PLL but with ADC signal.

Also Checked with software generated signal(50Hz) it is giving correct frequency result (50Hz).

Also I had measure the ADC signal, it is having proper waveform at ADC Pin.

What is the issue with the ADC block of TMS320F280037 ? 

  • 0
    TI__Guru* 84370 points

    Mahendra,

    Since we are reconstructing the signal to the frequency domain, the correctness of the ADC sample rate will be in play.  This is all determined by the accuracy of the system clock of the MCU.

    Can you look at the configuration of both the F2837x and the F28003x and confirm the clock source used for the MCU.  Specifically I'm looking to see if F2837x is using the external clock from X1/X2 and the F28003x is using the Internal oscillator.

    The internal oscillator on both these devices has a frequency tolerance +/- 1-3% dependent on the ambient temperature range.  If F2837x is using an external X-TAL or clock, then it will have much tighter frequency tolerance.

    Let me know what you find in terms of settings, certainly the FFT calculations will be impacted based on the accuracy of the main clock of the MCU, and as such the sampling rate of the ADC.

    There are small differences in the AC performance of the ADC on these devices, but I think the above is the correct place to start the investigation.

    Best,

    Matthew

  • 0 in reply to MatthewPate
    Prodigy 45 points

    Dear Matthew,

    Yes with TMS320F28379d it is with external clock (20Mhz), and in TMS320F280037 it is with internal clock INTOSC1(10MHz).

  • 0 in reply to Mahendra Gupta
    Prodigy 45 points

    Dear Matthew,

    After using external crystal of 16MHz, issue resolved.

    Thanks for your support.