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LM25069 TIMER capacitor voltage rating

Other Parts Discussed in Thread: LM25069

Can we use 6.3V rating capacitor as a LM25069 TIMER capacitor?
I think it is OK because TIMER pin upper threshold is 1.85V.

Best Regards,
Kohei Sasaki

  • Hi Kohei,

    6.3V cap should be ok since the max upper threshold is 1.85V as you had mentioned.

    We typically recommend a value of 10V because of cap bias derating (the capacitance will decrease as its voltage increases). Since this is used for a timer, just keep in mind that your effective fault time may be smaller than expected due to cap bias derating.

    This is why it is important to design with margin in mind. The fault timer should be set with some margin above the startup time in order to ensure the device powers up ok.

    We have an application note at www.ti.com/hotswap --> "Technical Documents" --> "Robust Hot Swap Design" for guidance on timer selection. Section 3.1.2.4 discusses how we typically recommend the fault timer to be set to 1.5x tstart in order to have 50% margin for things like power limit variation or capacitor bias derating.

    Thanks!

    Alex

  • Alex-san,

    Thank you for your reply.
    What voltage level is the internal pull-up source of timer pin. What level does the timer pin voltage rise up to if timer pin pull down function doesn't work?
    I would like to know about this as a reference information.

    Best Regards,
    Kohei Sasaki

  • Hi Kohei,

    The max voltage threshold at the timer pin is 1.85V. Look Below for the typical voltage specs of this device. I hope this answers your question.

    Best Regards,

    Aramis P. Alvarez

  • Aramis-san,

    I'm understanding about the timer pin max threshold voltage.
    I would like to know the internal pull-up source voltage of timer pin. 
    Doesn't timer pin become higher voltage than upper threshold even if circuit response delay is considered?

    Best Regards,
    Kohei Sasaki

  • Hi Kohei,

    I now understand your question. It can take several days to get this value from the IC design team. I talked to them and they stated that if your concern is the cap going above the power rating, that using a 10V cap will be fine. Was that your concern? Did you still want to know the value of the internal pull-up source voltage of timer pin? If yes, I'll send a request to the IC design team to fetch that value. Again, this might take several days. Thank you for your patience Kohei.
  • Aramis-san,

    Thank you for your reply.
    And I would like to know it. We want to know internal pull-up voltage value to judge 10V cap is no problem.

    Best Regards,
    Kohei Sasaki

  • Hi Kohei,

    I talked to the IC designer and he stated the nominal pull-up voltage is 5V at the Timer pin. I hope this helps :-)

    Best Regards, 

    Aramis P. Alvarez