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UCC28881: UCC28881 buck converter to output -12V with respect to VIN-

Victor Chen_HK
Expert 5130 points
Part Number: UCC28881

Hello,

Could you provide a reference circuit to make UCC28881 output -12V with respect to VIN-?

The input is 220V AC and customer wants to have a negative voltage output.

Thanks and best regards,

Victor

  • 0
    TI__Expert 5130 points

    Does Swaping D1 and L1(D1's anode connect to Vout), connecting D4's anode to VIN- and reversing CL make a negative output?

    Best regards,

    Victor

  • 0 in reply to Victor Chen_HK
    TI__Mastermind 40530 points

    Hello Victor,

    I believe that the High-Side Buck-Boost Converter configuration shown in Figure 23 of Section 9.2.2.4 in the UCC28881 datasheet fits the requirements of your customer. The marked-up changes you indicate in your previous posting do not quite match this Figure and lack a couple of disconnects that would make it conform to Figure 23.

    I recommend to use Figure 23 directly, rather than modify a different configuration, to eliminate any ambiguity about the connections.

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    TI__Expert 5130 points

    Hi Ulrich,

    The Figure 23 is Positive Output (VOUT) with Respect to VIN– yet my customer wants a negative output with respect to Vin-.

    Any suggestions on how to modify the circuit? Thanks.

    Regards,

    Victor

  • 0 in reply to Victor Chen_HK
    TI__Mastermind 40530 points

    Hi Victor,

    Perhaps I am misinterpreting your request, but as best as I can understand it, Figure 23 IS what your customer is looking for.
    Using VIN-as the reference, you can see that it coincides directly with VOUT+ as the same node.  That means that VOUT- is a negative output with respect to VIN-.

    Figure 21 shows the opposite case, where VOUT+ is a positive output with respect to VIN-, as described in the bulleted features list for this configuration.  While typing this, I noticed that the 2nd bullet for Section 9.2.2.4 with Figure 23 says "Positive Output (Vout) with Respect to VIN-" and this is wrong.  That is probably the source of confusion here.  That bullet should read as "Negative Output (Vout) with Respect to VIN-".  I'll submit this error in the datasheet to be corrected, although I can't predict when this correction will be released.

    Regards,
    Ulrich