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LT3579 Vout setting with DAC


For the LT3579 DC/DC converter I'm interested in the dual output as shown in the image below. I would like to be able to control the output voltage with 5V room (e.g. from 15V to 20V) with a DAC or digital pot. Would it be possible?

I tried adding a resistor under 130k resistor, which was tied to the ground (i.e. a divider), then connect a DAC (with a resistor in front) to the divider network. But this didn't work in LTspice simulation. One obvious solution is to add a variable resistor in series with 130k resistor, but I'm wondering if there are better solutions.

I'd appreciate any suggestions.