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TPL8002-25 digital potentiometer help

Caitlin Danehy
Prodigy 60 points
Other Parts Discussed in Thread: TPL8002-25, OPA2889

I am using the TPL8002-25 digital potentiometer.  I have pins 10-15 hooked to a microcontroller that will give it the high or low (binary) control.  I am having an issue getting a linear voltage drop when I input the different position values.  I have connected +12V to RG1, connected gnd to RF1 and taken voltage readings between RG1 and RSW1.  The voltage output values are up and down and frankly confusing.  The data sheet hasn't been much help with outlining a clear way to wire it up/test. 

I also have the OPA2889 (8 Pin SOIC).  I have hooked up the TPL8002-25 to the OPA2889 according to my interpretation of the "typical application circuit" on pg 2 of the data sheet.  Pin 1 (out A) was hooked to RF1, pin 2 (-In A) was hooked to RSW1, pin 3 (+In A) to gnd, pin 4 (-Vs) to RG2, pin 5 (+In B) to gnd, pin 6 (-In B) to RSW2, pin 7 (Out B) to RF2, pin 8 (+Vs) to RG1.  the + and - terminals of a 12V batter were hooked to RG1 and RG2 in this circuit.  I have my +/- 3.3V connected to pins 4 and 5 of the tpl8002 and gnd connected to pins 9 and 16.  I input the different binary values associated with different wiper positions within the digi pot, and connected my DMM across the outA and outB terminals of the OPA2889.  It reads voltage values that barely settle and are not intuitively what they should be. 

so my question here is, what am i doing wrong? I'll try to keep debugging but I really need some insight and help. 

Thanks.

  • 0
    TI__Intellectual 780 points

    Hi Caitlin,

    With regards to your first question, the TPL8002-25 is not a linear taper digital potentiometer.  The steps for this part were designed such that the ratio of (Rf/Rg) is linear in the logarithmic scale.  If you need linear steps, I would suggest that you take a look at the TPL0202. 

    One issue w/ your test setup is that the terminals of the digital potentiometer cannot be connected to a potential above that of it's own VDD/VEE supplies.  For example, if the supplies of the TPL8002-25 are +/-3.3V, then you cannot apply anything below -3.3V or above +3.3V on the resistor terminals.  That being said, we do not have any digital potentiometers that can handle the 12V on it's terminals.  Please provide me with more details on your specific end application and I can try to suggest an alternative.

    Thanks.