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UCC28951: PWM comparator

satoshi hasegawa
Prodigy 20 points
Part Number: UCC28951

Tool/software:

Is this correct that "the PWM comparator compares the CS+RAMP signal to the COMP pin. Once CS+RAMP exceeds COMP, the PWM pulse terminates" ?

  • 0
    TI__Guru* 86266 points

    Hello,

     

    Your inquiry will be reviewed and answered in the order it was received.

     

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 86266 points

    Hello,

     

    The CS is level shifted by 0.8 V and then summed with the slope compensation.

     

    Please note that that the controller does not terminate gate drive pulses to terminate the duty cycle.

    The comp pin then will phase shift the C and D pulses to control the duty cycle. A and D in phase or B and C in phase is 100% duty cycle.  A and D 180 degrees out of phase or B and C 180 degrees out of phase results in 0% duty cycle.

     

    The following equation shows how the duty cycle will vary vs comp voltage.

    Duty Cycle = Vcomp*100%/2V

     

    In current mode control it is as follows if the current sense resistor is selected to be at 1.8 V at 100% D.

    Duty Cycle = (Ipeak*Rcurrent_sense-0.8V)*100%/1.8 V

     

    Regards,