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How to change ADC resolution of F2812 by using IQ library?

Siyu He
Expert 1040 points

Hi,

I am using eZdsp 2812 to control a boost converter and I find out that the ADC resolution is too high which causes limit cycle oscillation. I am wondering how to change ADC resolution by using IQ function?

I compared the two expression below, it turns out the results are the same.

_IQ16toIQ((_iq)AdcRegs.RESULT2))

_IQ12toIQ((AdcRegs.RESULT2>>4))

He, Siyu

  • 0
    TI__Mastermind 43730 points

    hm..

    If you use the full ADC resolution then 

    _IQ12toIQ(AdcRegs.RESULT2)

    if you want to ignore the two lower bits which will reduce resolution, you can do the following

    _IQ10toIQ((int16)AdcRegs.RESULT2>>2)

    If you still have limit cycle then the issue may not be ADC resolution

  • 0 in reply to Manish Bhardwaj
    Expert 1040 points

    Manish,

    Thanks for your reply.

    The maximum resolution is 12 bits for ADC and the 4 last bit in register are 0, so the ADCRESULT should be trreated as a 16 bits binary as IQ16.

    If use full ADC resolution in Q format, it turns out the result is negative if MSB of AdcRegs.RESULT is not 0,so

    _IQ16toIQ((Uint16)AdcRegs.RESULT2)

    How do you think?

    He, Siyu