AD7715: Filter settling time

Document created by analog-archivist Employee on Feb 23, 2016
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The problem is that they give a step on the PT100 and the digital filter has a
certain settling time.
So each time they change the channel, they will have to wait for 3-4 samples to
read out correct values, cycles depending if they synchronize a filter
reset with the step given to the sensor

Would you confirm this?


When a step change occurs on the AD7715, the filter will require 3 conversion
cycles to settle. If DRDY is high before the channel change, DRDY will stay
high for 3 conversion cycles after the channel change.  When DRDY goes low, a
valid conversion will be available.  However, with the AD7715, if DRDY is low
before the channel change (i.e. another conversion has been completed before
the channel change occurs), the DRDY line stays low following the channel
change - it is not reset high.  In this case, a dummy read is required.  The
dummy read of the data register is needed before correct data gets loaded into
the data register.  So, in summary, one invalid reading may be received due to
the dummy read.  However, if sufficient settling time is allowed after the
channel change, the second reading (after the dummy read) should be valid.