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UCC28950: Min operating freq

Nir Flysher
Expert 3367 points
Part Number: UCC28950
Other Parts Discussed in Thread: UCC28951, UCC2895

Dear Team,

My customer would like to use a full bridge phase shift controller like the UCC28950 however he would like to operate it at low switching freq (Fsw).

On the UCC28950 recommended operating conditions table 6.3 on p.5 we specify min Fsw of 50KHz.

1. What is the reason for this limitation ?

2. What will be trade-off if the customer will chose to work at lower freq (let's say 10KHz)

3. Do we have a different controller that doesn't have this limitation ?

Best regards,

Nir

  • 0
    TI__Guru* 86286 points

    Hello,

    Your inquiry has been received and is under review.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 86286 points

    Hello,

    1. After reviewing the data sheet I would not use the device out of the characterized range.

    The minimum switching is 50 kHz based on figure 35 of the data sheet.

    2.  Not sure why the customer would want to design a ZVS based topology at 10 kHz.  Generally designers choose this topology to design at higher switching due not having primary switching losses.  This allows the designers to get the magnetic sizes down; as well as, reduce the magnetic DCRs which also reduce conduction losses.  Could you tell me what the customer wants to design for these low switching freqencies? 

    3.  I reviewed the UCC2895 and UCC28951 data sheets and there minimum switching is around 50 kHz as well.  So TI does not sell a PSFB controller that will work down at 10 kHz.

    Regards,

  • 0 in reply to Mike O'
    TI__Expert 3367 points

    Hi Mike,

    Thanks for the quick response.

    The customer wanted to check the possibility of leveraging existing magnetics being used on current project which are built for low frequencies.

    This is not the typical 'new design' project.

    Regards,

    Nir.

  • +1 in reply to Nir Flysher
    TI__Guru* 86286 points

    Hello,

    Thanks for letting me know.

    If the customer decided to go with the high frequencies using a PSFB they could reduce there magnetic size and losses as previously mentioned.

    At 10 kHz I am not shore that a ZVS based topology would by much of an efficiency improvement over what they are doing now.

    If you know the customers input and output power requirements, you might be able to find a better solution then they have in the TI reference design library. The following link will bring you to the library.  You just need to input the designs power requirements and do a search.  If TI has any reference designs that will meet there needs it will show up.  These designs have schematics, BOM, and test results.  They may be able use one of these designs without having to design new magnetics.

    https://www.ti.com/reference-designs/index.html

    Regards,

  • 0 in reply to Mike O'
    TI__Expert 3367 points

    This is exactly what the customer wanted to check.

    Thanks Mike.