Question description:
In DS1687 datasheet, the /KS pin has below definition, If not used, connect to Vcc or to VABUX if VBAUX is used.
But same pin in DS17887, it has reversed definition. If not used, /KS must be grounded and ABE set to 0.
Why DS17887 has same active low /KS but different access when not used? This is one TYPO or the right setting?
If the DS17887's /KS pin is connected to Vcc when not used, what will happen?
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Answer:
We think what to do with /KS on the DS1687 when the feature was not used, and since this was an open-drain, active low input, the response was to use a weak pull-up to a voltage (VCC or VBAUX). But later on with the encapsulated DS17887 design (ie, non-replaceable internal battery), current consumption concerns caused the us to add a recommendation to the DS17887 to keep the unused /KS connected to GND (with ABE and KSE bits set to 0) to reduce current leakage/draw from the /KS pins to extend the life of the internal battery. Leakage currents are less than 1uA (more like a few nanoamps) but any current savings helps.
So there is no functional difference between connecting /KS to a voltage or to ground when the ABE and KSE bits are 0. We think the difference is that the DS1687 uses an external/replaceable battery on VBAUX but the DS17887 has the non-replaceable internal lithium cell, and we want to mitigate any additional current draw, no matter how small.