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LM5175: Unexpected hiccup behavior

tateo yamashiro
Guru 10890 points
Part Number: LM5175
Other Parts Discussed in Thread: LM5176

Hi,

We got a question from the customer about LM5175.
Could you help us?

[Question]
- Is there any relationship between current limit threshold and slope compensation? During the input voltage transient condition, current limit threshold is shifted and unexpected hiccup is occurred. This phenomenon depend on Cslope value.

We can send the waveform and schematics by e-mail. We would appreciate it if you could provide us your e-mail address.

Best Regards,
tateo

  • 0
    TI__Guru* 78190 points
    Hi Tateo-san,

    Thank you and your customer for considering the LM5175.

    The current limit does change in different operating mode. In the pure boost mode, the current limit is about 160mV pk, and in the boost mode it is about 80mV valley. In the buck-boost transition mode, is limit is change to 80mV peak, and this is most probably where the limit was hit and hiccup mode was triggered.

    To avoid this, there are three options: (1) reduce the current sense resistor, (2) disable the hiccup mode by re-configuring the MODE pin, (3) change to the LM5176. The LM5176 is almost a drop in replacement of the LM5175, but you do need to change the RT resistor to stay in the same frequency. Please follow the datasheet selection guide to choose the new RT resistor if you select the LM5176.

    To answer your question: there is no relationship between the threshold and the slope compensation.

    Thanks,
    Youhao Xi
  • 0 in reply to Youhao Xi
    Guru 10890 points

    Hi, Thank you for your quick support. We got additional question. Could you please confirm this?

    - How much is the current limit threthold of LM5176 at the transition region?

    Best Regards,
    tateo

  • 0 in reply to Youhao Xi
    Guru 10890 points

    Hi, Are there any update on this? They would like to know the current limit behavior of LM5176 in the transition region. Sorry for rush, but could you give us your feedback by this Friday? We would appreciate it if you could give us your feedback.

    Best Regards,

    tateo

  • 0 in reply to Youhao Xi
    Guru 10890 points

    Hi, I checked the hiccup behavior of LM5176 in buck-boost mode by EVM. It seems the IC detects the current limit at Ics(buck). Please refer to the attached file for details.

    I assume the current limit threshold is not shifted in buck-boost mode. So I would like to make sure whether both Ics(buck) and Ics(boost) are active in buck-boost mode or not.

    LM5176 Hiccup Behavior_Aug2218.pptx

    Best Regards,
    tateo

  • 0 in reply to Youhao Xi
    Guru 10890 points
    Hi, Are there any update on that? Please let us know the current status regarding the current limit of LM5176.

    Best Regards
    tateo
  • 0 in reply to tateo yamashiro
    TI__Guru* 78190 points
    Hi Tateo-san,

    I was in a business trip in the past three weeks. Sorry for the delay. Unlike the LM5175, the LM5176's buck mode valley current limit, and the boost mode's peak current limit, are both active in the buck-boost transition mode. This is one of the improvements that we made in the LM5176 over the LM5175.

    Thanks,
    Youhao Xi
  • 0 in reply to Youhao Xi
    Prodigy 10 points

    Hello Youhao;

    We have a similar issue with a USB-C charger development, it uses lm5175 and a TPS2574A as the controller. The problem is on the slope signal that shows the following graphic configured to operate at 380kHz: 

    We think that this is the reason the MOSFETs don't trigger correctly and that's why we don't get voltage at the DCDC_OUT.

    I appreciate your time and if you could guide us on the process to find a solution.

    Thanks!

    Juan Manuel Morelli