Post Go back to editing

Range of PWM Duty Cycle on BF50x

Hello.

Reading the HW reference manual (rev 0.2) of the BF50x, I've found this phrase (page 14-15 or page 555 of the pdf document) about PWM duty cycle:

"Each duty cycle register range is from (–PWMTM/2 – PWMDT) to (+PWMTM/2 + PWMDT), which, by definition, is scaled such that a value of 0 represents a 50% PWM duty cycle."

This little confuse me because I understand that, in single-update mode, I can vary duty cycle from 50% to 100%: but if I need the whole range from 0% to 100%, how can I do?

In my application I have to drive an H-Bridge and I need to change each branch in the whole range from 0% to 100% and I would use (if possible) the single-update mode.

Thanks a lot for your help

Maurizio

  • HI Maurizio,

    As explained in HRM, the ‘PWM Channel Duty Control’ register holds two’s complement value of the Duty cycle.

    To understand this, consider an application (having SCLK = 100MHz) which generates PWM signal of 500 KHz.

    The switching frequency of PWM patterns is calculated as: PWM_TM = (100x10^6)/(2*500x10^3) = 100.

    So, the valid range for Duty Cycle Control register becomes (assuming zero dead time requirement):  -50(0xFFCE) <= PWM_CHA <= 50 (0x0032)

    …specifying -50 generates 0% duty cycle; 0 generates 50%; & 50 generates 100% duty cycle.

    So, Duty control register with –ve values, generates PWM waveforms of less than 50% duty cycle. HRM explains this clearly. Not sure whether you have any confusion any over specific information in it. Let me know if you have any questions.

    Best Regards,

    Prashant

  • Hi Prashant,

    thank you very much for your well explanation. I thought that the value for PWM_CHx, was intended as unsigned, and this fact was at the beginning of my misunderstanding.

    Sorry for this!

    Thanks again

    Maurizio