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UCC28910: About Primary Over-Current limit

Ryoma Ohashi
Expert 5085 points
Part Number: UCC28910

Hi team, 

My customer is considering to use this device and has a question about the current limit.

In the datasheet, it says

"If the DRAIN current exceeds IDOCP (~33% higher than ID_PEAK(max)), such as when IPK pin is shorted to GND, or VCSTE_OCP / RIPK, (VCSTE_OCP ~33% higher than VCSTE(max)), and the condition is sensed for three consecutive switching cycles, a fault shutdown and retry sequence, detailed in the output overvoltage fault description, occurs."

If the swtching frequency is 35kHz, will the delay be about 28.5usx3=85.7us?

Also, could you check if my understanding is correct?

Ipk: Current limit threshold to move to Constant Current mode

I_DOCP: if exceed this for 3 cycle, the device will shut down

I_DOCP2: if exceed this, device will shut down imediately

Regards,

Ohashi

  • +1
    TI__Guru 50140 points

    HI Ohashi-san,

    To answer your questions:

    If the switching frequency is 35kHz, will the delay be about 28.5usx3=85.7us? *Yes, but the UCC28910 uses AM/FM control law so the frequency varies as a function of load. See below:

    Also, could you check if my understanding is correct?

    Ipk: Current limit threshold to move to Constant Current mode

    I_DOCP: if exceeds this for 3 cycles, the device will shut down *Yes

    I_DOCP2: if exceed this, the device will shut down immediately *Yes

    I hope this helps to answer your question. 

  • 0 in reply to JCHK
    TI__Expert 5085 points

    Hi JCHK,

    Thanks for your support. My customer is considering to use this deivice as non-isolated ACDC like the schematic below

    https://www.ti.com/tool/PMP10766

    In other supplier's device, they have a function like LEB as below. Does UCC28910 has such kind of delay in the OCP?

    I was wondering if the 3 cycle of delay is equevalent to LEB.

    Regards,

    Ohashi

  • +1 in reply to Ryoma Ohashi
    TI__Mastermind 24375 points

    Hi Ohashi-San,

    UCC28910 has over current protection and blanking implemented.

    OCP protection is implemented as follows:

    If the DRAIN current exceeds IDOCP (~33% higher than ID_PEAK(max)), such as when IPK pin is shorted to GND, or VCSTE_OCP / RIPK, (VCSTE_OCP ~33% higher than VCSTE(max)), and the condition is sensed for three consecutive switching cycles, a fault shutdown and retry sequence occurs. If the DRAIN current exceeds a second level of current (VCSTE_OCP2 / RIPK) it is not necessary to detect the fault for three consecutive switching cycles, the device will stop switching immediately.

    There is a minimum on time of 390ns which emulates the LEB described above.

    Thank you

    Regards,

    Harish