I have a WTC set up so the current limiting is set to 1.2 A (3.12 kΩ) on the cooling side (LIMA) and 0 A (1.5 kΩ) on the heating side (LIMB). Why is the WTC3243 able to put out as much as 1.8 A when the set point called for more cooling current than the LIMA setting was supposed to allow? Just how ‘hard’ is the current limiting—brick wall cutoff or really soft, or somewhere in between?
The current limit is a “brick wall.” But the unit could exceed the limit if the RLIM resistor circuit is open or if you exceed the SOA (Safe Operating Area) with too high a voltage across the output stage.
Check to make sure that the RLIM circuit is closed. If it is closed and not the cause of the problem, see the Application Note AN-LDTC01: The Principle of the Safe Operating Area to calculate the maximum safe voltage. If you have used the WTC3243 at a higher voltage than is allowed as determined by the SOA chart, the WTC3243 may have been damaged and may need to be replaced.
If you still go beyond your set current limit, after determining that you have not gone beyond the Safe Operating Area, the WTC3243 may be otherwise damaged. Please call us for further assistance at (406) 587-4910.