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Original question:

LM5180: About RSET resistor accuracy

LM5180: IC behavior with decreasing RSET

Conor
Mastermind 9330 points
Part Number: LM5180

Tool/software:

Hi,

The "Related Questions" section mentions the value of RSET. The datasheet recommends RSET=12.1kΩ. Will the accuracy of VRSET decrease if the RSET value is reduced from 12.1kΩ?

Also, can you give us your opinion on how much worse the VRSET variation should be expected to be when RSET is reduced to 6.2k~6.8kΩ?

It may be difficult to get your opinion because the data sheet specifications (I_REST, V_REST) ​​were tested under the condition of RSET=12.1kΩ. In that case, I would like some advice in the following form.

- 6.2kΩ to 6.8kΩ is too small, and there is a high possibility that the IC will not operate normally.
- Because TI only tests at 12.1kΩ, it is necessary for your company to thoroughly evaluate and decide on resistance values ​​other than the recommended value. etc.

Thanks,

Conor

  • 0
    TI__Guru 73830 points

    Hi Conor,

    Thank you for designing with the LM5180.  You are very right that we recommend RSET=12.1k for the best Vout regulation accuracy because the IC is trimmed with RSET=12.1k.  We could have integrated RSET internally but we leave it external in order for the user to choose the matching type of resistors for both RSET and RFB to minimize Vout setting point tolerances. 

    Could you explain why you want to choose RSET differently?  Sorry I cannot tell how much Vout error would be introduced if you change RSET to 6.2k~6.8k, because we did not have such characterization data.  Although I don't think the IC will break, we just cannot guarantee the promised regulation accuracy.  Since the datasheet EC table is a legal contract, we do not recommend to choose a different RSET resistor. 

    If you have further questions, please let me know and we can work together to resolve the issue. 

    Regards,

    Youhao

  • 0 in reply to Youhao Xi
    TI__Guru 73830 points

    Hi Conor,

    May I close this thread for no activities in 2 weeks?  You are welcome to reopen it by adding a new post.

    Thanks,

    Youhao