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ADuM2251 static output loading question

Hello,

I am using ADuM2250 as I2C isolator, in datasheet recommended operation conditions, it specifys static output loading of minimum 0.5mA, as attached. my question is whether or not it is necessary to maintain more than 0.5mA loading, and what will happen if it is zero?

The application is new energy vehicle, it is crital to keep as low as possible power consumption.

Thank you & best regards

Ben

ADuM2251.ppt
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  • Hi Ben,

    The quick answer is nothing catastrophic happens if you go below 0.5mA.  However, the static load is set by the pullup resistors on the bus, as apposed to the dynamic load of the bus capacitance. A pullup at some level is required for operation, otherwise there is nothing to pull the line high when the outputs turn off.  The static loading assumes a low is being driven, and the static load is the pullup.  When the outputs are high, the current through the pullup resistors is zero in any case.

    If you do want to make those pullups as large as possible to minimize current, you can do that, but the operation will slow down proportionately.  The pullup is part of the RC combination that pulls the line high, and that slows down if R gets too big.

    Best Regards,

    MSCantrell

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  • Hi Ben,

    The quick answer is nothing catastrophic happens if you go below 0.5mA.  However, the static load is set by the pullup resistors on the bus, as apposed to the dynamic load of the bus capacitance. A pullup at some level is required for operation, otherwise there is nothing to pull the line high when the outputs turn off.  The static loading assumes a low is being driven, and the static load is the pullup.  When the outputs are high, the current through the pullup resistors is zero in any case.

    If you do want to make those pullups as large as possible to minimize current, you can do that, but the operation will slow down proportionately.  The pullup is part of the RC combination that pulls the line high, and that slows down if R gets too big.

    Best Regards,

    MSCantrell

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