I am interested in having dynamic control of the output current limit circuit of a DC-DC converter controller (the LTC3777 buck-boost controller in my case). This IC has a built-in current limit using an external high-side shunt resistor, which is monitored directly by the IC.
From looking at the datasheet, it appears that the two sides of the shunt resistor go directly to the inputs of a differential amplifier inside the chip, which is then tied into the rest of the feedback loop. What I would like to do is somehow modify that differential signal from the shunt resistor, so I can dynamically control the current limit setting using a microcontroller equipped with either with a DAC or digital POT.
My initial idea is to insert a differential amp (or current sense amp) in between the shunt and controller IC, and then adjust the gain of the amplifier to effectively control the current limit value. However, I'm concerned about this extra element introducing instabilities into the feedback loop due to the slight propagation delay said amplifier would introduce to the circuit.
Is the concern valid? Or are there other, more robust/simple approaches to do this (aside from controlling the current limit with a separate, independent circuit)?