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UCC256303: burst mode, Latch,

kwnag woon Lee
Prodigy 170 points
Part Number: UCC256303
Other Parts Discussed in Thread: UCC256403

Hello, currently I am making a 2kW ac/dc converter with UCC256303.

I amd developing a converter that can change the output voltage from 43V to 56V / 37A.

Currently, it operates at 200kHz under the load condition of about 10A at 43V output voltage, and the waveform is shaken (or burst mode?) and then latches after a while.

Is there a condition under which UCC256303 can become a latch?

I think there are a few questions about the latch on UCC256303 in this forums.

I'm worried because I can't find the solution.

And I want to set the current to enter burst mode. Please explain how to set it.

Because PFC is applied, 390V fixed voltage is used as input of LLC converter.

Please review.

Best regards.

Kwang woon Lee

  • 0
    TI__Expert 8210 points

    Kwang woon Lee

    First off we recommend that you use UCC256403 instead.  UCC256403 is a generational improvement over UCC256303 that is pin-to-pin compatible (some passive R/C values do change though).  The following app note has details on these improvements and how to migrate a design from UCC256303 to UCC256403 http://www.ti.com/lit/an/slua966a/slua966a.pdf

    To program bust mode the following sections of the corresponding datasheets have details

    • UCC256403 datasheet: Section 8.4.3 (page 35) and section 9.2.2.19 (page 60) 
    • UCC256303 datasheet:7.4.1 (page 31) and section 8.2.2.19 (page 54)

    If there is excessive high frequency noise on the ISNS pin in UCC256303 there is the potential that it could shut down.  UCC256403 does not exhibit this shut down behavior.  If your design is shutting down, and you have confirmed that it is not a fault protection, we recommend you switch over to UCC256403.

    Best Regards,

    Eric