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UCC28704: UCC28704 Brown in and Brown out

Pao Wu
Intellectual 920 points
Part Number: UCC28704

Hi All,

How to setting brown out. Do you have simulation tool could share to us??

Following description from datasheet page.20. Is it brown out function??

Input Under-Voltage: The line input run and stop thresholds are determined by current information at the VS pin
during the MOSFET on-time. While the VS pin is clamped close to GND during the MOSFET on-time, the current
through  R S1 ,  out  of  the  VS  pin,  is  monitored  to  determine  a  sample  of  the  bulk  capacitor  voltage.  A  wide
separation of run and stop thresholds allows clean start-up and shut-down of the power supply with the line
voltage. From the start state, the sensed VS current, I VSL , must exceed the run current threshold, I VSL(run) (typical
220 µA), within the first three cycles after switching starts as VDD reaches V VDD(on) . If it does not, then switching
stops and the UVLO reset and re-start fault cycle is initiated. Once running, I VSL must drop below the stop level,
I VSL(stop) (typically 80 µA), for three consecutive cycles to initiate the fault response.

Thanks.

  • 0
    TI__Mastermind 31580 points
    Hi Pao,

    I have asked one of our applications engineers to respond to your post. You should see a response soon.

    Regards

    Peter
  • 0
    TI__Expert 5900 points

    Hi Pao,

    For the description of page 20, related to IVSL(run), it is brown-in.

    related to IVSL(stop), it is brown out.

    For equation 23 on page 29, Vin(run) is the brown in voltage.

    To calculate Brown out voltage, you could replace the IVSL(run) with IVSL(stop).

    Br

    Kening

  • 0 in reply to Kening Gao
    Intellectual 920 points

    Hi Kening,

    Do you have simulation tool or Calculated Excel file could share to us??

    Thank you for your information.

  • 0 in reply to Pao Wu
    TI__Expert 5900 points
    Hi Pao,
    On the page of UCC28704, we provided pspice model, Mathcad tool and excel tools.
    www.ti.com/.../toolssoftware

    Hope this can help you.
    If you have any other concerns, please feel free to let us know.

    Br
    Kening
  • 0 in reply to Kening Gao
    Intellectual 920 points
    Hi Kening,
    I has try IVSL(Stop) function.
    This brown out point varies from load to load. (5V/2A brown out 60V, 5V/1A borwn out 50V, 5V/0.1A 40V.)
    It can't used in my design.
    Do you have suggested external cirucit for brown out??
  • 0 in reply to Peter Meaney
    Intellectual 920 points

    Hi Peter,

    Could you please help to support this case??

    We want to add brown out circuit in UCC28704.

    Do you have any suggest??

  • 0 in reply to Pao Wu
    TI__Mastermind 47695 points

    To make the described brownout protection, a peak voltage detector is needed to detect the input ac voltage peak value. The peak voltage value is used to make UCC28704 VDD undervoltage lockout off when a selected input voltage brownout point reaches. Then the described brownout function is achieved.

    One possible way is to use the circuit shown below. Dpc, Rpc and Cpc are formed for peak voltage detection along with the existing high voltage start resistor Rst1. When the input voltage is at brownout point, its corresponding peak voltage is detected. Then U2A output becomes low. Zpc clamps U1 (UCC28704) VDD to 6.8V < 7.3V so U1 is forced to UVLO OFF. The input brownout shutdown is achieved.

    When the brownout condition is removed, U2A output becomes high. U1 VDD clamp due to Zpc is removded. U1 operation will be back to normal. U2A is an open collector voltage comparator.

    Note this is a circuit proposal for precise input brownout protection to show basic addition and how it should work. No test has been made yet.

  • 0 in reply to Hong Huang
    TI__Mastermind 47695 points

    (Resend as the circuit drawing is not shown in the last message.)

    To make the described brownout protection, a peak voltage detector is needed to detect the input ac voltage peak value. The peak voltage value is used to make UCC28704 VDD undervoltage lockout off when a selected input voltage brownout point reaches. Then the described brownout function is achieved.

    One possible way is to use the circuit shown below. Dpc, Rpc and Cpc are formed for peak voltage detection along with the existing high voltage start resistor Rst1. When the input voltage is at brownout point, its corresponding peak voltage is detected. Then U2A output becomes low. Zpc clamps U1 (UCC28704) VDD to 6.8V < 7.3V so U1 is forced to UVLO OFF. The input brownout shutdown is achieved.

    When the brownout condition is removed, U2A output becomes high. U1 VDD clamp due to Zpc is removded. U1 operation will be back to normal. U2A is an open collector voltage comparator.

    Note this is a circuit proposal for precise input brownout protection to show basic addition and how it should work. No test has been made yet.