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UVLO setting of LM43602

Shinichi Inoue
Guru 21626 points
Other Parts Discussed in Thread: LM43602

Dear Specialist

My customer is designing LM43602.

UVLO threshold is different from the equation.

Could you teach me the reason.

The detail is listed below.

Vin=24V, threshold voltage=18.8V

According to the datasheet 9.2.2.11 Under Voltage Lockout Set-Point

equation(24) VEN=Vin-uvlo*RENB/(RENB+RENT)

Vin-uvlo=2V (using for worst case UVLO Voltage 18.8V）

Choose the value RENB=1Mohm

It is calculated RENT=8.2Mohm.

Actually, UVLO on-threshold voltage is 22.5V, UVLO off-threshold voltage is 19.7V.

It has a difference between calcuｌated and actual.(20% difference )

ON the other hand, threshold 22.5V stands for the UVLO threshold is 2.45V.

What is the problem?

I think total resistance is high(1Mohm + 8.2Mohm).

Is it a cause of problem?

Best regards,

Shinichi

  • 0
    TI__Genius 16025 points
    Hi Shinichi,

    We've received your request and will get back to you shortly.

    Thanks,
    Anston
  • 0
    TI__Genius 16025 points
    Hi Shinichi,

    Happy to help! The total resistance is too high for this scenario as it now approaches 10MOhm. Hence small variations in the input current are significant since the current into the EN pin hovers around a few uA.

    The typical 1Mohm Renb value is suggested for Vin's that are 12V and below. THis will need to be adjusted as the input voltage increases.

    If you decrease the resistances to 820kOhms and 100kOhms, the tolerances should reflect what you calculated. Remember your quiescent current is also dependent on this value.

    Thanks,
    Anston
  • 0 in reply to Anston Lobo
    Guru 21626 points

    Dear Anston 

    Thank you for your reply.

    I will send your advise to the customer.

    I appreciate your great help!

    Best regards,

    Shinichi