AD8564: I/P common mode range

Document created by analog-archivist Employee on Feb 23, 2016
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I want to use the fast Comparator AD8564 for my Design. In the datasheet is the
parameter Vcm  declared. The Voltage Range is limited to +2.75V. But the
absolute maximum range of the anlaog input channel is much higher (+/-7V).
Has the Vcm only affects on the Commen Mode rejection ratio? Or does the
comparator works obove the range not properly even if the same voltage lies
only a few nanoseconds at both input pins?


The AD8564 uses a PNP differential input stage which enables the input
common-mode range to extend all the way from the negative supply rail to within
2.2 V of the positive supply rail. The input common-mode voltage can be found
as the average of the voltage at the two inputs of the device. To ensure the
fastest response time, care should be taken to not allow the input common-mode
voltage to exceed this voltage.

In addition to the above, you will notice that the graph of input bias current
against i/p common mode has a knee shape at this point. i.e 2.2Volts from the
+ve rail.