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TMS320F2800137: HRPWM worse case resolution calculation

Part Number: TMS320F2800137

Hi,
should I use max MEP step size of max 310ps or typ 150ps (DS, 6.13.2.1.1) to calculate the HRPWM resolution (UG, table 13-15).

I think the typ and max value (DS, 6.13.2.1.1) is only valet by using the SFO? Is SFO mandatory or optional to use?

Regards, Holger

  • Hi Holger,

    It is always recommended to use AUTOCONV to calculate the appropriate MEP step size because this step size will vary according to temperature and voltage of the device. SFO is highly recommended with auto conversion enabled. Using the MEP step size of 150ps should be good to calculate HRPWM resolution.

    Best,

    Ryan Ma

  • Hi Ryan,

    in the UG it was 180ps for the calculation (table 13-15) used.

    Regards, Holger

  • Hi Holger, 

    Using the typ, from the datasheet is what I would recommend, unless the end application will be operating under high temperature and minimum voltage on VDD as the MEP step size will increase to the 310ps. In the TRM the 180ps is for the examples on calculating MEP steps and I assume this was the first number used before characterizing the typical values on the datasheet.

    Best,

    Ryan Ma

  • Hi Ryan,
    customer wants to calculate the possible resolution with the HRPWM. I think for calculated values in the UG 180ps was used:

    Regards, Holger

  • Hi Holger, 

    To calculate possible resolution with HRPWM you can do 

    HRPWM resolution (%) = F_PWM / F_MEPSTEPSIZE * 100

    HRPWM resolution (bits) = log_2( T_PWM / T_MEPSTEPSIZE)

    For example:

    Assume F_PWM = 1MHz, F_MEPSTEPSIZE = 1 / 150ps

    HRPWM resolution (%) =  1 MHz / (1 / 150ps)  * 100 = 0.015 

    HRPWM resolution (bits) = log_2( (1/1*10^6) / 150ps) = 12.7 bits

    Best,

    Ryan Ma