I have a need for regulated +/-15V from an unregulated bipolar supply that may range from 25-35V under varying load conditions. I want to use a buck converter so I don't have to heat sink anything. Efficiency is not really a concern for this. For the positive side I plan to use MCP16331 and it seems straightforward.
For the negative side I had a hard time finding examples that took a negative voltage and stepped it "down" to a negative voltage of lower absolute value. Mostly there are examples of a positive-input, negative-output buck-boost configuration. However I found this application note for a switching controller with a similar idea but somewhat more complicated. What I'm taking from that application note is the method of referencing the feedback voltage to the input supply common rather than the controller's "GND" pin, which in this case is actually the input voltage.
The feedback pin of the MCP16331 should be 0.8V above the GND pin when in regulation, so the idea here is to use a current source to keep the feedback pin 0.8V above the "N15V_RTN" net, which is the same as the input VNEG net at DC, when the output voltage is -15V. That way VNEG can vary from -25V to -35V but the regulator should keep the output at -15V since it's referenced to the supply common rather than the converter's own GND pin.
See any glaring problems with this?
For the negative side I had a hard time finding examples that took a negative voltage and stepped it "down" to a negative voltage of lower absolute value. Mostly there are examples of a positive-input, negative-output buck-boost configuration. However I found this application note for a switching controller with a similar idea but somewhat more complicated. What I'm taking from that application note is the method of referencing the feedback voltage to the input supply common rather than the controller's "GND" pin, which in this case is actually the input voltage.
The feedback pin of the MCP16331 should be 0.8V above the GND pin when in regulation, so the idea here is to use a current source to keep the feedback pin 0.8V above the "N15V_RTN" net, which is the same as the input VNEG net at DC, when the output voltage is -15V. That way VNEG can vary from -25V to -35V but the regulator should keep the output at -15V since it's referenced to the supply common rather than the converter's own GND pin.
See any glaring problems with this?