If you read the datasheet of the IC, it isn't really current regulation but current limiting that is possible. See page 9:
"Output Current Monitoring and Regulation
The LTC3649 has the ability to accurately sense the average inductor current without the use of an external sense resistor. The IMON pin output current is 1/40000th scale of the inductor current.
In addition to simply sensing the inductor current, the LTC3649 can also be programmed to regulate the aver-age output current limit. The regulator will limit the peak inductor current if it senses that the voltage on IMON has exceeded 2V."
As a general remark, when you are regulating voltage into a variable load, you can really only do one of two things:
- try to keep voltage at some fixed value (up to the maximum current that the device will supply, after which you are forced to reduce voltage to prevent damage). This is voltage regulation.
- try to keep current constant, up to some maximum voltage, with the same restriction. This is current regulation.
You can do one or the other at any given time, but not both.