My 18V to 12V MPQ2908 buck converter shows pulse pairing with one long duty cycle followed by a short duty cycle. What can be the reason and what can I do?
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As 18V to 12V is relative high duty cycle, the actual inductor di/dt might be too high for the internal slope compensation. 1) try a larger L-value; if this does not help
2) Check the selected ILIM range and the used shunt resistor. Is there enough signal for a reasonable signal to noise ration? Is there enough headroom towards the sense voltage limit?
3) Modify control loop compensation. Increase C-comp, decrease R-comp. Add a capacitor directly from COMP-Pin to GND, 100pF…1nF
4) Check effective Cout, in case only ceramic capacitors are used.