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UCC25660: Recommended TSET programming

RUSTY BOUDREAUX
Prodigy 40 points
Part Number: UCC25660

Any guidance on programming TSET?

Datasheet gives minimum frequency for IPCC operation but does not mention issues with setting it too low.  For example, if maximum frequency is 600 kHz what are the ramifications of TSET option #1 (48.9 kHz)?  Why not use option 1 for all switching frequencies?  What advantages to choosing a TSET with higher minimum frequency (assuming normal operation is above that frequency)?

  • 0
    TI__Genius 13275 points

    Hi,

    The TSET option needs to be chosen as per the minimum frequency of the converter. The TSET option determines the internal time constants and the timer gain of the internal VCR generator.

    For ex: If the minimum frequency in the application is 80kHz, I would choose any TSET option which can support 80kHz or below.

    Regards

    Manikanta P

  • 0 in reply to Manikanta Pallantla
    TI__Genius 13275 points

    Hi,

    I tried to run simulations with 390V input and 12V, 15A output which has 100kHz resonant frequency.

    I used two different TSET options for simulations keeping ISNS and VBLK resistors same.

    When I used option 5 the VFB replica is 3.8V during steady state whereas when I used option 1, the VFB replica is 2.52V. You could see that the dynamic range of VFBreplica has reduced by choosing the lowest option.

    Regards

    Manikanta P

     

  • 0 in reply to Manikanta Pallantla
    Prodigy 40 points

    Thank you, Manikanta P.

    If I understand this means you recommend using the highest option that is below the minimum frequency so as to maximize dynamic range of VFBreplica.  Is this correct?

    The table also has columns for 3.5V OCP and 4V OCP.  What are the ramifications or reasons for choosing 3.5V or 4V for OCP?

  • +1 in reply to RUSTY BOUDREAUX
    TI__Genius 13275 points
    RUSTY BOUDREAUX said:
    If I understand this means you recommend using the highest option that is below the minimum frequency so as to maximize dynamic range of VFBreplica.  Is this correct?

    Yes, that is Correct. Also, it makes the burst mode settings less tolerant to Resistance values variance.

    RUSTY BOUDREAUX said:
    The table also has columns for 3.5V OCP and 4V OCP.  What are the ramifications or reasons for choosing 3.5V or 4V for OCP?

    The selection of OCP would be depending on the application. If you are okay with giving additional stress on the primary side of MOSFETs (especially during startup), you can use the OCP option of of 4V.

    Regards

    Manikanta P