Tool/software:
Hi,
I am working on a design for the LM5146 buck converter controller and would like it to operate in CC/CV mode with the following specifications:
Input: 27V to 72V
Output: 25.2V 10A
After following the instructions in the LM5146 datasheet (Page 24) which states that: "Given the large voltage swings of ILIM in RDS(on) sensing mode, a capacitor designated CILIM connected from ILIM to PGND is essential to the operation of the valley current limit circuit. Choose this capacitance such that the time constant RILIM· CILIM is approximately 6 ns.", and an ILIM resistor value of 470 ohms from the online LM5146 Calculator, I have added a CILIM of 10pF for a time constant of 4.7 ns.
However, when load tested with a constant resistance load and an input voltage of 36V, the controller does not seem to perform valley current limiting and instead hiccups immediately when drawing around 10A from its output. After replacing the CILIM with a higher 100pF value, the valley current limiting works to limit the current but at a higher output current of around 12.5A. May I know how approximate (higher, lower?) should the time constant be in the ILIM RC circuit and what the consideration behind 6 ns was? What should the correct implementation be for a design with a variable output current limit?
The circuit diagram of the buck converter circuit is attached below according to the RDSon Current Sensing Mode.
Thank you.
