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UCC28070: UCC28070 have some question

Lawrence He
Genius 3280 points
Part Number: UCC28070

Dear,


our client design UCC28070 as below chart, but we find the some question.

1. If Vsense >3.18V  to trigger OVP and then off PWM, if Vsense is 0, PWM also turn off?

2. UCC28070 Brown-in and Brown-out point,  reference which one pin?

3. PKLMT is reference CSA and CSB voltage, if over PKLMT voltage, ic how to protection ? protection mode is duty?  Latch?


4. If PKLMT is 3.63v, output current 8.7A, and CSA and CSB voltage is 1.6v, but output voltage 383V drop to 376V, why drop issue?

if any, Please advise me.

Thanks,

Best regards,

Lawrence.

  • 0
    TI__Mastermind 34465 points
    Hello Lawrence,
    (1) PWM is off when VSENSE is less than 0.75V
    This is called the enable voltage and is a safety feature that shuts down the pfc in case the feedback has become open loop.
    (2) Brown-out/brown-in is achieved with the VINAC and VSENSE pins.
    For gate drive on GDA/GDB you need VINAC to be greater than 0.7V and VSENSE greater than 0.75V
    There is no dedicated brownout pin.
    (3) Once PKLMT is detected the controller disables that gate drive until the next clock cycle initiates a gate drive.
    It is a non-latching cycle by cycle current limit.
    (4) If the PKLMT comparator is triggered it will cause the output voltage to drop.
    This can be useful if the inductor is saturating and it is an extra safety feature.
    The pfc should be designed so that PKLMT is triggered only for an abnormal condition.

    Regards
    John
  • 0 in reply to John Griffin1
    Genius 3280 points

    Hi, John


    about question 2, if Vin 90Vac drop to 84 Vac, PWM will be turn off, because VINAC under 0.7V?
    and how to Measurement UCC28070 Bode plot; voltage loop( VSENSE) serial 100 ohm could be test point?

    if any, Please advise me.

    Thanks,

    Best regards,

    Lawrence.

  • 0 in reply to Lawrence He
    TI__Mastermind 34465 points

    Hi Lawrence,

    If VINAC is less than 0.7v at 84Vac input then the UCC28070 will shut down.
    You can do a Bode plot by placing a small resistor in the VSENSE resistor network.
    50 Ohms to 100Ohms is a good value to use

    Regards

    John

  • 0 in reply to John Griffin1
    Genius 3280 points

    Hi, John


    about PKLMT & CSA question:


    Ch1: CSA , Ch3:VBULK , Ch4: choke current as below chart,

    we find the question:

    CSA did not under 3.63v, but VBULK from 383v drop to 376v, and choke current is not in saturating.

    why VBULK will drop?

    if any, Please advise me.

    Thanks,

    Best regards,

    Lawrence.

  • 0 in reply to Lawrence He
    TI__Mastermind 34465 points

    Hi Lawrence,

    I spoke to a colleague here about this and he suggested that perhaps you are measuring Vout with a DMM under no load and read 383V

    This would be the peak charged voltage of the output caps.
    Then you apply a load and the DMM reads 376V which would be an average reading including ripple.
    Is this possible ?

    Also your schematic does not show the VSENSE divider line.
    There must be some series drop in this line that changes VSENSE with load.

    Regards

    John

  • 0 in reply to John Griffin1
    Genius 3280 points

    HI, John

    1. output load: 0~8A, DMM read value 383V (VBULK)

    2. output load: 8.7~8.8A, DMM read value 376V (VBULK)

    if we up to more loading, VBULK voltage also keep to drop, is  ic  triggered to protection ? protection mode is  Peak current limit? Duty?

    below chart schematic:

    if any, Please advise me.

    Thanks,

    Best regards,

    Lawrence.

  • 0 in reply to Lawrence He
    TI__Mastermind 34465 points
    Hi Lawrence,
    Did you use the calculator tool and make sure the correct value of RIMO was used ?
    Regards
    John
  • 0 in reply to John Griffin1
    Prodigy 10 points
    Hi John
    I have a question for UCC28070,
    The Bulk voltage rises form 383Vdc to 389Vdc in burn-in(3000W),
    Can you explain this phenomenon? thanks
  • 0 in reply to benson Tseng
    TI__Mastermind 34465 points
    Hi Benson,
    Can you please start a new thread for this question so we can keep track of both issues separately ?
    Thanks
    John