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UCC28063: Could not support expected load current during start up

Part Number: UCC28063

The customer is using UCC28063 + L6598 (ST) to realize PFC + LLC. The input voltage range is 100~230V, and PFC output voltage is about 390V. The output voltage of LLC is +/-60V.

This project is from OEM. OEM offered schematic and PCB layout to our customer.

When our customer imported the file from OEM, they found the package layout became larger. So they changed some layout to avoid warning from Altium Designer. (The original file type is unknow, the software our customer used is Altium Designer.)

Below is the OEM board:

 

Below is the board of customer:

 

Below is the schematic of UCC28063.

 

Due to the policy and confidential, it is available to get the schematic and layout file now.

In test, they add load current to LLC, and then start up the circuit. (100V input voltage)

For OEM board, up to 650W (about 5.4A) could be added and the circuit could be started up normally. If larger load current is added, LLC circuit would go into protection.

While for the board of our customer, only about 500W (about 4.1A) could be added and start up normally. If larger load current is added, PFC circuit would go into protection.

And customer reflects that, if the current load is added step by step, such as from 4.1A to 4.8A, and then to 5.4A, the board of customer could support up to 650W.

And if the input voltage is 230V. Both OEM board and their own board could support up to 650W during start up test.

I have compared the layout, I have found that on customer board, the capacitors for several sensing pin (such as CS, VSENSE) is relatively far away from pin than OEM board. It would be easier to couple noise.

Do you think it would be the key reason to lead this issue?

Any suggestion to figure out the problem and is it easy to verify that if don’t make a new PCB?

Thank you.

  • Hello Robin,

    I have referred your question to the appropriate team for this device. Please look for an answer soon.

    Regards,
    Ulrich
  • Hi,

    The first issue I notice is that PHB is connected to COMP.

    This is done in an attempt to switch off GDB at light load.

    Unfortunately this will not work if the input voltage varies from 100V to 230V because the value of COMP varies with line and load

    Please remove the resistor from PHB to COMP

    This allows GDA and GDB to operate over the full load range.

    Also please check the value of RSET (pin 3) on the OEM's board and the customers board.

    The value of the resistor on the TSET pin sets the maximum on time for the UCC28063.

    If maximum on time is set too low then the power supply will be unable to provide full power at low line voltage.

    Hopes this helps.

    Regards,

    John

  • Hi John,

    Thanks for your quick reply.

    Actually, the resistor from PHB to COMP has been taken off. (You could see R311 is not soldered in the PCB picture)

    And the components and parameters used in both OEM and customer's board are the same.

    I would let customer to try different TSET.

    Same schematic and parameters but big difference for actual performance.

    Any other suggestion?

    Thank you.

    Robin

  • Hi Robin,

    If you wish to send me the original design files I can ask our pcb department to check what software was used.

    They may be able to translated them to Altium .

    Maybe worth a chance.

    My email is johngriffin@ti.com