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UVLO accuracy of LM43602

Shinichi Inoue
Guru 21686 points
Other Parts Discussed in Thread: LM43602

Dear Specialists

My customer is evaluating LM43602.

UVLO threshold is higher than expected, because ｔotal UVLO resistance is too high(1Mohm + 8.2Mohm).

For more information is listed URL below

http://e2e.ti.com/support/power_management/simple_switcher/f/858/t/400526

The problem was sold by deducing resistance  820kOhms and 100kOhms.

The customer wants to know the relationship between resistance value and error voltage.

Could you please advise me.

He thinks 820k+100k is too low and increases quiescent current. 

Best regards,

Shinichi

  • 0
    TI__Genius 16025 points
    Hi Shinichi,

    The 820k+100k was a suggestion. It was stated earlier that a resistance of a lower decade would increase quiescent current. The customer is correct. The ideal value would be somewhere in between 100k and 1M. Probably around 500kOhms.

    As the Rent and Renb value increases to 1M+8.2M, the enable current drops to about 24uA, for a 24Vin. Since the enable control current is only 1.75uA, as spec'd in the datasheet, the control current is now significant and this causes accuracy to be limited.

    Hope this helps.

    Thanks,
    Anston
  • 0 in reply to Anston Lobo
    Guru 21686 points
    Dear Anston

    Thank you for your reply.

    Could you confirm my consideration?

    When Rent and Renb is 1M+8.2M, enable current is 2.4uA.( not 24uA I think)
    On the other hand, enable current is 1.75uA.
    They are close, therefore voltage error was caused.

    If resistance change to 500k+4.1M(half value), the current increased to 5.2uA.
    the error is smaller.

    The resistance change to 100k+820k, the current is 26uA.
    the error should be more smaller.
    The resistances is smaller(the current increases), the error voltage is smaller.

    There is trade-off between the resistance and accuracy.

    Best regards,
    Shinichi
  • 0 in reply to Shinichi Inoue
    TI__Genius 16025 points
    Hi Shinichi,

    My apologies for the typo. I did indeed mean 2.4uA. Yes there is a trade-off between the resistance and accuracy.

    I will proceed to close this thread.
    Thanks for spotting the typo.
    -Anston
  • 0 in reply to Anston Lobo
    Guru 21686 points
    Dear Anston

    Thank you for your reply.

    I understand.

    I'll explain to the customer.

    I appreciate your great help!

    Best regards,
    Shinichi