18V regulated from battery using LT1054

[decc]

I've got an LT1054 supply circuit put together in the same manner as the popular MAX1044 one, but I want to use the additional regulation feature this chip offers in order to get a stable 18V across the range of voltages a battery can supply over its usable life. There is an example of a 5V to regulated 8V supply ("positive doubler with regulation") in the datasheet here:

http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1039,C1014,P1258,D2309


However this uses an op-amp and a few more extra caps/resistors. I was hoping this could be done with a simple two-resistor divider. Is there any reason that one couldn't set it up with a simple divider that provides 0.7V to the feedback pin when the output is 18V? Am I completely misunderstanding how this pin works?

[decc]

Guess I should take more time to read and understand the problem before posting.

For those interested, simple version: if the voltage at the feedback/shutdown pin goes below ~0.45 V it turns off the pump, if above it runs as normal. So the op-amp is needed to invert the difference between the actual output and desired output so that under-voltages result in a higher value at the FB pin and visa-versa.

(And as long as we're throwing in another 8-pin DIP for the op-amp may as well make it a dual and use the second one to get a regulated Vref.)