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TMS320F28027: Incorrect clock frequency

Dylan You
Intellectual 2630 points

Part Number: TMS320F28027

Dear Teams,

My customer is using TMS320F28027 EVM, and they have following requirement. Could you help give some suggestions here?

They used LAUNCHXL-F28027, and want to change the ADC's clock to 1Mhz. Their current setting is: 

1. Window size to 7

2. SoC set to 2

3. Clock frequency is 50Mhz

4. ePWM set to 50

Thus, the output should be 1Mhz. However, they connect the ePWM to the GPIO and test it with oscillscope, then they found the actual clock frequency only has 120kHz.

Could you help give some suggestions here?

Thanks!

Dylan

  • 0
    TI__Guru 62975 points

    Dylan,

    It sounds like they are trying to verify the EPWM frequency? Can you confirm? I am not entirely sure how the provided ADC configuration is relevant to the EPWM frequency.

    I recommend verifying the SYSCLK frequency using XCLKOUT first.

    -Tommy

  • 0 in reply to tlee
    TI__Intellectual 2630 points

    Hi Tlee,

    I have told customer that they are not able to set the EWPM frequency to 1Mhz. Their key requirement is: How to set 1Mhz sampling frequency for ADC module?

    Thanks!

    Dylan

  • 0 in reply to tlee
    TI__Intellectual 2630 points

    They want to have 1MSPS sampling rate for ADC to sample 512 point.

  • 0 in reply to Dylan You
    TI__Guru* 84660 points

    Dylan,

    If the sampling rate has to be exactly 1MHz, then as you said the ePWM can't match that with a 60MHz system clock.  We would get 999.8kHz or 1.016 MHz.  Customer could change the CPU clock to 50MHz, so that we can get an even multiple of 10us.

    I think we run into the same issue even it we use continuous conversion of the ADC with a change in ACQPS.  At the end of the day, we are bound by multiples of CPU clock or 16.67ns at 60MHz.

    Does customer need exactly 1MSPS sampling, or could they be OK with one of the above multiples?

    Best,

    Matthew