UCC256301: UCC256301 for LCC

Hi Jerry,

Thanks for your interest in UCC256301. During startup, the voltage on the LL/SS pin sets the switching thresholds until the internal FBreplica is less than the LL/SS pin voltage at which point, the controller transitions control to the feedback loop. It is possible to see some burst cycles during start up even at heavy load depending on the feedback loop compensation.

At steady state and heavy load, do you also see burst operation or only during startup?

Best Regards,
Ben Lough

Hi Ben,
Jerry’s questions are that there are also  burst mode can be seen in stady state or heavy load. At the case 2 burst on cycles is too close to cause hard switch as the first pictures below. the picture shows lots of  hard switches  which are caused one burst on cycle by next burst on cycle. at the light load the burst mode are normal which are burst on --- burst off ---burst on as the second picture and no hard switches any more. what are the root cause?

Thanks in advance

Zhou

Hi Zhou,

Thank you for the additional information. is the FB pin voltage oscillating at steady state? This would cause the controller to continuously move in and out of burst mode. Could you share the schematic? You can email it to me if you do not want to post the schematic publicly. ben.lough@ti.com.

Best Regards,
Ben Lough