--- In "charliem_1216" <> wrote:
>
> --- In "tseredynski" <tseredynski@> wrote:
> >
> > Hello,
> >
> > I've tried looking at the ts-7250 datasheet and manual, as well as the
> > MAX197 datasheet, but I am still unsure of the settling time when switching
> > channels on a ts-7250 with MAX197 ADC (optional component for the ts-7250).
> > Would anyone happen to know how much time it takes for the signal to
> > stabilize when switching channels, before I can take a new reading?
> >
> > The closest I got to finding out was in the datasheet of the MAX197:
> >
> > http://datasheets.maxim-ic.com/en/ds/MAX197.pdf
> >
> > on page 8, at the end of the first paragraph it says
> >
> > "A low impedance input source, which settles in less than 1.5μs, is
> > required to maintain conversion accuracy at the maximum conversion rate."
> >
> > Which I can't decide if that means that the settling time is then at most
> > 1.5us, or if that just means it will take the next reading in 1.5us and I
> > need to make sure that my signal is stable before then...
> >
>
> Well, closest to the latter. It is describing the output impedance you need
> to have in your source conditioning circuit, so that the input is not still
> settling when the 197 T/H goes from Tracking to Holding. The analog value at
> that time will be digitized, whether the signal is settled or not.
>
> Sounds like they are describing the settling time of the input MUX without
> really coming out and saying it. Most chips can take consecutive samples on
> one channel faster than they can with a channel change, but I don't see that
> described here.
>
> The timing diagrams explain in more detail.
>
> regards, ........ Charlie
>
> > Can anyone help me out?
> >
> > Thanks,
> >
> > Tyler
> >
>
when changing chanel the load on the cicuit you are sampling will change. The
circuit must respond to this change and become stable in under 1.5 us to allow
time for the chip to complete it's convertion and return a result within the
minimum sample time if you want to work at the max sample rate of the 197.
from memory the fastest sampling period for the 197 is 6us. So it requires a
minimum of 4.5 us to sample a stable voltage after the initial 1.5 us .
One of the outputs signals when the data is ready so it's not really a case of
waiting 6us before sampling, rather waiting until the chip indicates the data
it ready.
All this is rather acedemic on TS7250 as supplied since the since the 100Hz
system clock means the fastest you can get from the driver is 10ms (yes you
lose three orders of magnitude on what the 197 is capable of doing).
If you want faster sampling a fair bit of work will be required.
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