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AD5290 digi pot, weird effects

Question asked by stevek80 on Jul 12, 2013
Latest reply on Jul 15, 2013 by DRice

Hello,

 

I recently got an AD5290 for evaluation, I put it in a test circuit with +/- 15 V analog power supply rails, and hooked the SPI lines up to an MCU devboard.
There is one GND connector, pin-4, which is designated as "digital ground".

However, I only get sensible output, i.e. measured DC resistance via DMM between terminals W and B (pin 10 and 2),

if I also connect the digital ground to the 0V center of my analog dual supply.

If that's the case, I can adjust the output resistance to the whole specified range.

If it's not connected, the output was seemingly random the other day, today it seems to remain at about 25 kOhm.

 

Just in case my PSU is to blame, I also tried it with two 9V batteries, same result. If the zero volt center is not connected, I measure nonsense, if it is connected to "digital ground", it works perfectly.

 

Now according to the datasheet this shouldn't be the case, and it also seems weird, since some people would probably not like to connect their analog ground to the digital one at that point.

 

EDIT:

Let me add that I have been told elsewhere that the datasheet mentions that analog and digital ground should be "remotely connected".
In a bigger circuit than my testcircuit they are, indeed "remotely", connected, and it doesn't work. It works as soon as the "digital ground" pin gets a dedicated wire to the analog ground connector on my board. That I find even weirder, but I'm an inexperienced hobbyist ;-)

 

What could be wrong here? Could this behavior be a result of damage due to experimenting with the chip? (I remember having grilled one when I first tried them out many months ago, corrected the circuit, and then put things aside for a while, I'm not sure why that one now should be damaged, but who knows)

 

Regards,

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