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UCC256301: LLC controller for HV to LV DC-DC converter without X cap discharge (or selectable)

Chris Cencula38
Prodigy 120 points
Part Number: UCC256301
Other Parts Discussed in Thread: UCC256303, UCC256302

In looking at the UCC256301, it appears that there is no way to turn off the X cap discharge if it is being powered from a DC source.

In another post, I see reference to some 'dash' versions of the part that might have this feature either disabled or selectable, but the answer there indicates that the UCC256301 is the only part that is released (no dash versions).  Does TI have a similar part that doesn't have the X cap discharge (or has it as a selectable/programmable feature such that it could effectively be avoided?)  We're expecting the DC to have relatively little ripple, so a capacitive coupling to a zero crossing sense pin may not be a reliable means of defeating the feature.

Thanks,

Chris

P.S.  We're looking to have a very high efficiency (above 90%, preferably above 95%) Isolated HV DC to LV DC supply (approximately 300Vin, ~ 13Vout)

The input voltage suffers from poor line regulation at the light load end of the spectrum, possibly coming close doubling in value with zero load, so startup/OVP will have to be also considered/worked-around as well.

  • 0
    TI__Mastermind 27095 points
    Hi Chris,

    Thank you for your interest in TI. UCC256303 is a similar device which does not an x-cap discharge function:www.ti.com/.../UCC256303

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 120 points
    Hi Ben,

    I should have mentioned that I saw this part, but it apparently doesn't offer the HV startup, so would need additional power supply circuitry, I believe. Do you have a part with HV startup that doesn't have the X-cap discharge (or has a way of turning it 'off' or essentially defeating the function - maybe by addition of components? In the application, there will be HV DC supplied to the circuit and we need as high efficiency as possible, so we can't have the X-cap discharge current wasting power.

    Thanks,
    Chris
  • 0 in reply to Chris Cencula38
    TI__Mastermind 27095 points
    Hi Chris,

    UCC256302 is an LLC resonant controller with HV startup and no x-cap discharge (this device will be available on ti.com next week). This guide talks briefly about UCC256302:www.ti.com/.../slyt728.pdf.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 120 points
    Hi Ben,

    This description in the guide sounds very promising for our application.
    The only concern I have is that these parts appear to be meant for driving LLC converters that can be fairly high power, relative to the power level we are looking at - the HS and LS gate drives are probably quite a bit larger than what I'm guessing will be necessary to drive the half-bridge for our supply. I'm sure this is to make the part suitable for a fairly wide range of applications. What I'm wondering is if there is any data from evaluation work that TI has done that might give us an idea of the 'overhead' required by a converter utilizing one of these series parts that is supplying ~15W from ~300VDC input (or put another way, do you have any efficiency data for a low power converter based on one of these parts?)

    Also, you mention that the part will be on ti.com next week - would it be possible to get a preliminary data sheet and start the process for obtaining a few samples before then?

    Thanks,
    Chris
  • 0 in reply to Chris Cencula38
    TI__Mastermind 27095 points
    Hi Chris,

    UCC256302 has a tunable burst mode function that aims to increase light load efficiency. If your output voltage ripple requirement is not too strict, you could design your LLC to always operate in burst mode in order to achieve higher efficiency. I don't have efficiency data for a low power 15W LLC design unfortunately.

    I'm not able to share the device datasheet at this time but what I can do is send you a message once the datasheet becomes publicly available.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 120 points
    Hi Ben,

    Do you have an update on the availability of the UCC256302 datasheet and samples?
    Last week you mentioned that it would be available on TI.com this week - wondering if there is any issue with the release?

    Also wondering if the pinout of this part will be the same as the UCC256301?
    If yes, then I could probably start working on a PCB layout and even some preliminary testing before the UCC256302 is available.

    Thank you &
    Best regards,
    Chris Cencula
  • 0 in reply to Chris Cencula38
    TI__Mastermind 27095 points

    Hi Chris,

    UCC256302 should be available online within the next day or so. Pinout is the same, you just need to connect the HV pin to the PFC output instead of AC line.

    Best Regards,

    Ben Lough

  • 0 in reply to Benjamin Lough
    TI__Mastermind 27095 points
    Hi Chris,

    The datasheet is now available online. Orderable samples should become available soon as well.

    Best Regards,
    Ben Lough