My customer uses ICC28950. When the load current is above 20A, they found OUTC and OUTD would become abnormal (Duty variance)
Could you advise where to check the situation?
Rock,
I signed the OUTA/B/C/D according to my guess. it seem that it is sub-harmonic oscillation issue. So, please confirm if UCC28950 working on PCM(peak current mode).
1,In order to verify it is sub-harmonic oscillation issue, you can recommend customer change the working mode from PCM to VMC( voltage mode control). Customer can connect the Rsum to Vref to configure VMC. If there is no this issue on VMC, we can verify this issue is sub-harmonic oscillation issue. Then customer can re-configure the working mode back to PCM. Then Customer refer the 7.3.11 in UCC28950 datasheet to debug the Slope compensation.
2, Customer need to pay attention the function of ZVS is achieved when the mosFET C/D ON moment. If there is hard switch situation, the C/D pulse drive may been turn off by spike current. please double check the waveform of PIN cs. Avoid to mosFET hard switch, customer can increase the delay time and increase the inductance of Lr.
In addition, I see that the Duly cycle approximate to 100% at 20A load. in order to get more output power range,I think you can suggest customer to reduce transformer primary Np to reduce D at this load condition.
thanks
