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TIDA-00961: reasons why toff_calc and ton_adj_dbg are formulated as in sample code?

Pin Chia Pan
Prodigy 40 points

Part Number: TIDA-00961

Having some questions about the way toff_calc and ton_adj_dbg are formulated in.

In controlISR, why did you design the part in toff_calc to be toff_calc*acSine_diff*toff_adj_percentage, which I guess is the additional toff to achieve ZVS, rather than just calculating the time you need theoretically from values of Vin, Vout, inductance and capacitance, and letting the zvs code in pwmISR to compensate the deviation of the calculated value? What is the purpose or advantage of the method in sample code?

As for ton_adj_dbg, I couldn't figure out a convincing reason of adding this time to ton_calc. Would you explain why?

Thank you for help.

Best,

Amy

  • 0
    TI__Expert 3860 points

    Hi Amy,

    The toff extension is for achieving ZVS. However, there will be a distortion in current waveform if only toff is increased. We need to extend ton also to maintain the average current profile (to compensate for the excess negative current). I will also let the firmware Engineer to respond to your query.

    Regards,

    Salil

  • 0 in reply to Salil
    Prodigy 40 points
    Hi Salil,

    Thanks for the reply. I would like to ask another question. In controlISR, is new_ton_calc added to ton_calc in order to keep minimum on time during like zero crossover state in which output of the PI controller of the current loop might be close to zero? Looking forward to the response.

    Best,

    Amy
  • 0 in reply to Pin Chia Pan
    TI__Genius 10820 points

    Hi Amy,

    ton_calc is made up of two parts. One part comes from the voltage loop (new_ton_calc) and the other part comes from the current loop (ton_iloop_adj). During the zero crossover state the ton_calc value is slowly increased using the variable ton_calc_soft  to provide soft-start for the active GaN FET. 

    I hope this helps.

    Hrishi

  • 0 in reply to Hrishi Nene
    Prodigy 40 points
    Hi Hrishi,

    Since ton_iloop_adj also comes from voltage loop, is ton_iloop_adj alone not effective enough to voltage response? Is new_ton_calc designed to add a direct influence on on time, comparing to indirect influence by new_ton_calc?

    Thank you for help.

    Amy
  • 0 in reply to Pin Chia Pan
    TI__Genius 10820 points
    Hi Amy,

    Sorry for the delay. You are right. The voltage loop output works as a coarse adjustment command for the ON time, while the current loop output works as a fine adjustment command.

    Hrishi