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Original question:

UCC28730-Q1: UCC28730-Q1

UCC28730-Q1: UCC28730-Q1

rick Yu
Prodigy 120 points
Part Number: UCC28730-Q1

Hi,

Q1: I don't understand why Dmax is derived at fmax? From below formula, the duty cycle is minimum when switch frequency is maximum, isn't it?

:

Q2: I don't understand the principle why Dmagcc is fixed internally at 0.432, it is the secondary winding conduction radio Td/Ts right? How to make it a fixed value at CC mode? Can you share  a CC model control block diagram to understand.

Q3, My design will works at CV mode, rather than CC mode, how to set it works in CV mode rather than CC mode?

  • +1
    TI__Guru 65805 points

    Hello,

    Q1: this is because how the controller was designed to work with control law that uses FM/AM/FM modulation and constant on time control.  When less duty cycle is needed the frequency decreases to obtain less duty cycle.

    Q2:  The device was designed to operate with a Dmag time of 0.432 if you use something more there could be control issues.

    Q3:  Constant current mode is great for battery charging.  If the device reaches the maximum current will deliver that current when the output voltage is at 80%, 60% and 40% of it's maximum.  If you do not want you design to operate in CC mode, just insure the load is less the maximum.

    Regards,