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UCC256302: UCC256302 for an output power of 2KW

selvam perumal
Intellectual 525 points
Part Number: UCC256302
Other Parts Discussed in Thread: UCC27714

Hi,

I am going to use UCC256302 as an half bridge LLC regulator for converting 320V to 50V @ 40A.

1.In UCC256302 datasheet Page no:14,It is mentioned as that the internal driver can drive LLC power stage upto 500W continuous power.

Shall I use external gate driver for higher drive current for my mosfet?If drive current is an issue.

2.Is there any provision to fix the minimum switching frequency of regulator IC  to 650Khz in order to avoid the transformer saturation.

  • 0
    TI__Mastermind 27085 points
    Hi Selvamperumal,

    Thanks for your interest in UCC256302. For 2kW, you would likely need either a full bridge LLC or phase shifted full bridge topology. With either option, you will need an external driver. There is not a provision to set the minimum switching frequency on UCC256302 unfortunately. Could you help me understand why your design calls for a minimum switching frequency of 650kHz? Is it to minimize the size of the magnetics?


    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Intellectual 525 points
    Thank you for your response.
    Yes,Minimum switching frequency is to minimize the magnetics.
  • 0 in reply to selvam perumal
    TI__Mastermind 27085 points
    Hi Selvamperumal,

    Thank you for the clarification. Based on your resonant tank design, you can bound the minimum switching frequency to a value above 650kHz. The lowest switching frequency will occur at maximum power stage gain. The largest required power stage gain will occur at minimum input voltage and maximum output power.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Intellectual 525 points
    Thank you,
    To avoid the switching frequency less than 650KHZ,
    1.I can lock the minimum input voltage with BLK pin.
    2.I will limit the maximum output power by input current sense.
    Could you please clarify on below queries
    Qn1.Is there any other parameter to be considered to avoid the switching frequency less than 650Khz?
    Qn2.If I use external gate driver for the Primary MOSFET,The inbuilt adaptive dead time sensing will work or not?
    If not,Shall I go with the external gate driver with programmable dead time.
    Qn3 I designed my resonant circuit with the frequency of 650KHz.If at any case,my regulator IC tries to switch at lower frequency say 35KHz,Will it damage my magnetic components(Transformer capable of transferring output power of 2KW at Fmin:650Khz)
  • 0 in reply to selvam perumal
    TI__Mastermind 27085 points
    Hi Selvam,

    The minimum switching frequency for an LLC converter occurs at minimum input voltage and full load. You will want to make sure your power stage is able to provide sufficient gain margin without falling below 650kHz.

    You will still need to connect the HS pin of UCC256302 to the primary side switch node even if you use external gate drivers.

    It is possible to damage your magnetics if the switching frequency drops too low. At full load condition, a lower switching frequency will result in larger peak currents in the primary and secondary. This could damage the power stage and possibly saturate the transformer.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Intellectual 525 points
    Hi Benjamin,
    1.HO pin of UCC256302 will be connected to the input of my external gate driver.
    If I connect the HS to switch node,HO pin which connected to the External gate driver input will have (Vsw +VHB) potential w.r.t to ground.
    This would damage the external gate driver.
    Can you share any application note for using UCC256302 with external gate driver?
  • 0 in reply to selvam perumal
    TI__Mastermind 27085 points
    Hi Selvam,

    Below is an example using UCC256302 with UCC27714, a high-side + low side gate driver:

    1. connect UCC256302 LO to UCC27714 LI
    2. connect UCC256302 GND to UCC27714 VSS
    3. connect UCC256302 HO and HS to a gate transformer primary side and the secondary side connects to UCC27714 HI and VSS. (this is to translate the internal floating driver logic of the high side to a ground referenced signal. 1:1 turns ratio is fine for the gate drive transformer).
    4. connect UCC256302 HS to UCC27714 HS and connect both pins to the primary side switching node.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Intellectual 525 points

    Hi Benjamin,

    Thank you for your response.

    I am planning to use GAN FET:GS66516B-E01 for primary switches.

    As in the application note:It is suggested to go with isolated converter for above GAN device .

    1.Shall I use UCC21520ADW for driving the GAN device instead of UCC27714.

    2.Can you suggest any 1:1 transformer for switching frequency upto 1Mhz  .