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PMP20495: Design intention question

Kazuki Itoh
Genius 9175 points
Part Number: PMP20495
Other Parts Discussed in Thread: UCC28710, UCC28631, UCC28910

Hi team,

Could you please let me know the role of R2 connected in parallel to D2 in PMP20495?

I'd appreciate if you attach the relative app note of high-side buck regulator design.

Best regards,

Kazuki Itoh

  • 0
    TI__Expert 5435 points

    Hi Itoh-san, 

    Thanks for the question, I asked Sheng-yang to get back to you. We are currently traveling at a conference, please excuse the delay.

    Thanks,

    R2

  • 0 in reply to Robert Taylor1
    TI__Expert 3660 points

    As a PSR Flyback controller is used in this design and the PSR Flyback controller UVLO level is determined by the current flow out from the VS pin, R2 gives a current flow path to set UVLO level. 

  • 0 in reply to Sheng-yang Yu1
    TI__Genius 9175 points

    Hi Sheng-yang-san,

    Is R2 mandatory?

    My customer modified PMP20495. The R1=10k, R3=10k, and R2 is not used.

    The UCC28710 is replaced by UCC28631.

    I found related app note of non-isolated high-side topology with UCC28910.

    https://www.ti.com/jp/lit/an/snva750/snva750.pdf#page=6

    In the UCC28613 datasheet, , AC Line UV and Brownout feature is described, but its hard to find specific threshold and design procedure.

    Best regards,

    Kazuki Itoh

  • +1 in reply to Kazuki Itoh
    TI__Expert 3660 points

    Itoh san,

    Sorry for my late reply. A current outflow path is mandatory if you are using UCC287xx PSR control VS pin for UVLO sensing. In the application note Figure 5, a different path is provided for VS pin outflow current - R2 and R5.

    Regards,

    Sheng-Yang Yu

  • 0 in reply to Sheng-yang Yu1
    TI__Genius 9175 points

    Hi Sheng-Yang-san,

    Could you please help me to calculate the R2 and R5 for UCC28631 non-isolated HS buck topology?

    The IVSL(run) is not described in UCC28631 datasheet.

    Vbrownin and Vbrownout looks like same as ACON and ACOFF on table 6 (80VAC and 65VAC respectively).

    I understand this is a difficult question.

    My customer has tried UCC287121 previously and found that the output voltage dropped when the >0.5A  Iout.

    So my customer chose UCC28631 and now it is hard to change as it's close to the production. We do need your help to address this.

    Best regards,

    Kazuki Itoh

  • +1 in reply to Kazuki Itoh
    TI__Expert 3660 points

    Kazuki san,

    I am not aware of any UCC28631 HS buck design. And I think it might not work. The output voltage drop your customer has faced might be due to near field noise coupling to the current sensing. It is very critical to use shielded inductor like I did in PMP20495 with UCC287xx controller. Please double check with your customer if they have applied a shielded inductor.

    Regards,

    Sheng-Yang Yu

  • 0 in reply to Sheng-yang Yu1
    TI__Genius 9175 points

    Hi Sheng-yang-san,

    Ok, I'll check with PL regarding IVSL(run) of UCC28631.

    Yes, the PMP20495's indusctor is supposed to be surface mount inductor 74435571500 from Wurth, but in the photo L2 looks like bulky and different.

    I didn't realize it is carefully shielded. I'll let my customer know that.

    Best regards,

    Kazuki Itoh