Hi,
I am using the LM5022 in a SEPIC Design with the following specification: 9-30V input / 12V @1A output
I have started with a design in WeBench and checked these suggested values by working through the SEPIC design calculations from the LM3481 datasheet, a very similar part.
WeBench recommends a 0.075mR sense resistor and a 2.32kR series resistor to current limit at 1 amp. However the design is not limiting at 1A. I have already damaged several ICs trying to find at what point it is limiting.
The LM5022 datasheet states:
"The LM5022 provides a cycle-by-cycle over current protection function. Current limit is accomplished by an internal current sense comparator. If the voltage at the current sense comparator input exceeds 0.5V, the MOSFET gate drive will be immediately terminated."
I have scoped the waveform on the CS pin, but it is nowhere near 0.5V at 1A load, its about 250mV pkpk. I have tried to adjust the series resistor value, but it makes very little difference (if any) to the voltage on the CS pin.
I have checked that the resistor values on the PCB are correct, replaced the switch and the controller IC. I have checked my calculations and the design on WeBench but can't see where I am going wrong. WeBench design attached.
Any ideas?
Thanks
Tim