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bq24032A - datasheet clarification - current required for pulling ISET2, PSEL & CE high

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Asier Azaceta
Posted by
on Mar 21 2012 04:48 AM
Intellectual430 points

Hi all,

I'm designing a charging circuit based on bq24032A and I want to pull ISET2, PSEL & CE HIGH, and for the sake of simplicity I plan to pull the three of them up with a unique resistor.

Reading the datasheet I see that there are some input current limits in the electrical characteristics for these inputs, which for the max value read: 40uA for ISET2, nothing for PSEL and 1uA for CE. Are these values about the max current those inputs will draw? or is it the max current that can be input into them?

My Vcc is from USB or AC through some schotty diodes, so the voltage would be around 4.3-5v, and I'm using right now a unique 100k resistor for the pull-up for three of them. Does it look ok to you?

Thanks,

Asier.

bq24032a ISET2 CE PSEL
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  • Tahar Allag
    Posted by
    on Mar 22 2012 17:06 PM
    Genius13560 points

    Asier,

     The numbers you are reading the datasheet are not the maximum absolute values. To be in the safe side, use about 200K as pull up resistor.

      -Tahar  

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  • Asier Azaceta
    Posted by
    on Mar 23 2012 04:57 AM
    Intellectual430 points

    Hi Tahar,

    Thanks, I will change it then, but for the sake of satisfying my curiosity, are those values then the current drawn?

    Thanks again. Regards,

    Asier.

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  • Tahar Allag
    Posted by
    on Mar 23 2012 08:18 AM
    Genius13560 points

    Asier,

    Yes, the positive direction of the current indicates the input current into the pin and the negative direction indicates the the current out of the pin.

    -Tahar  

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  • Asier Azaceta
    Posted by
    on Mar 23 2012 09:27 AM
    Intellectual430 points

    Hi Tahar,

    Then am I right supposing a pull-up resistor of 200K is for keeping current into "reasonable" values but that I don't have to "target" (for instance) 40uA for ISEL2?

    As far as I can read the only max value to be aware of regarding those inputs is the input voltage that has to be kept under 7v, right?

    I'm trying to learn something out of this, so, please, excuse me if I keep pushing questions. I just want to learn what to take into account for calculating the pull-up resistor here.

    Thanks again for your kind support,

    Asier.

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  • Tahar Allag
    Posted by
    on Mar 23 2012 13:17 PM
    Verified Answer
    Verified by
    Genius13560 points

    Asier,

     Those pins are high impedance. The currents listed in the electrical characteristic table are leakage current but at the same time you do not want to over stress them with small reisitors, thus 200K pull up resistor should be good. The most important parameter here is the voltage level. In the absolute maximum rating table, the 7 volts is the max voltage. The thresholds are 0.4V for lower level and 1.4V for the high level.     

     Thanks

    Tahar

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  • Asier Azaceta
    Posted by
    on Mar 26 2012 02:38 AM
    Intellectual430 points

    Ok, I think I get it now.

    Thanks a lot for your help.

    You guys are giving a great support here at the e2e forums! Keep it going!

    Best regards,

    Asier.

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