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TPS25924: About RL(su) of TPS259240

watanabe
Expert 1740 points
Part Number: TPS25924

Hi,

My customer has a question.

Q.

"RL(SU) Load at start-up 4 Ω"
This above is written by datasheet(P17 9.2.1.1 Design Requirements).

"RL(SU) Load at start-up 1000 Ω"
This above is written by datasheet(P21 9.2.2.1 Design Requirements).

Is this difference due to the presence or absence of output blocking FET?

Best regards,
Watanabe

  • 0
    TI__Guru* 96061 points
    Hi Watanabe,

    The difference is not due to presence of blocking FET.
    The output capacitance and output load resistance forms as load during startup. For larger capacitive loads, there is a limit on RL(SU) load value at start-up. If the RL(SU) value is low, it will drain the charging current and hence output voltage does not built up.
    As you see, for "RL(SU) Load at start-up 1000 Ω" case, the capacitance is 4700uF.
    Please use the design calculator with your parameters to verify.

    Regards,
    Rakesh