Digital Pot usage question

[Charlie E.]

Hi All,
Ok, redesigning things again...

Considering using a digital pot as the calibration setting for my
ambient light sensor, so just using it as the feedback resistor in my
bufer stage. Any gotcha's I should know about, or other
idiosyncracies?

Thanks,
Charlie

 

[Fred Bartoli]

Vladimir Vassilevsky a écrit :

Digital pot is RC-RC-RC-RC-RC... It will oscillate like hell if you
don't dump it properly.

^^^^^
That sure is the word

Also mind the tempco, which is good as a divider, but might not be so
good as a resistor.

 

[Fred Bartoli]

Fred Bartoli a écrit :

Vladimir Vassilevsky a écrit :

^^^^^

The carets should obviously underline "dump".

 

[D Yuniskis]

Hi Charlie,

Ok, redesigning things again...

Considering using a digital pot as the calibration setting for my
ambient light sensor, so just using it as the feedback resistor in my
bufer stage. Any gotcha's I should know about, or other
idiosyncracies?

Are you sure you need to make the adjustment there instead
of twiddling bits? I.e., how much "extra" range do you have
in your measurement circuitry that you could exploit?

When dealing with things like this, I tend to use integrating/
counting converters. So, I can just change the period to
get the precision I need and massage the "readings" internally.
"Calibration" is then just storing factors "someplace"
(sometimes, this is a *volatile* parameter and the device
can "relearn" its calibration data as part of normal operation)