Hi, I would like to build Digitally-Controlled State-Variable Filter. See on page 13 in http://www.ti.com/lit/ds/symlink/tlc7528.pdf. The problem is that data converter TLC7528 does not operate as shown in datasheet. Specifically formula "DAC equivalent resistance equals: (256)x(DAC ladder resistance)/(DAC digital code)" does not apply. Between pins Uref and Iou I get resistance only 10-40 kOhms. Do you have any experience with this circuit?
Thanks, Jan.