LM5021: LM5021

This is a 2 switch forward converter application that will need to be spread spectrum'ed to achieve regulatory compliance plus the noise margin.

It appears that there is something done inside the chip at the LM5021-2's internal clock at its following edge not at my sync time since the LM5021-2 does not maintain 50% or less duty cycle when my sync pulse occurs after half way point of the LM5021-2's naturally set clock cycle. But when my sync pulse is at or sooner than the half way point of the LM5021-2's clock cycle, or my sync pulse is at or greater than twice the natural clock frequency, I have never seen output duty cycle greater than 50%. Could you check on this? 

Hi Paul,

Thank you for the additional information. Could you share what the value of your Rt resistor is and what is the frequency range of your sync pulse?

Best Regards,
Ben Lough

Rt = 124K ohms
Pulse is a positive pulse at 133khz.

Hi Paul,

Could you confirm you are seeing >50% duty cycle with Rt=124kΩ and Sync pulse frequency =133kHz? If this is not the case, could you share what value of Rt and what sync frequency you see >50% duty cycle?

Best Regards,
Ben Lough

Yes, it is never more than 50%.
If I change Rt to 71.5K ohms and watch the oscilloscope closely, there will be greater than 50% cycles which lead me to think inside the LM5021, there is something going on if a natural clock edge is within a certain time of my sync pulse. My sync pulse amplitude goes to roughly 8v with a time span of 100ns.