We are working on a boost design that accepts 12.5V - 21V input and delivers 90V at 500W. During bring-up, we have found that the circuit underperforms, only delivering about 150W instead of the intended 500W. The proximate cause seems to be that the circuit is falling out of CCM mode (compare the two oscilloscope captures, CCM_Correct.png and CCM_Fault.png). But we can't figure out why exactly that is happening or how to prevent it.
I have attached the relevant part of the schematic (Stage 1 boost.png) showing the circuit as initially built.
Over the course of testing, we have made the following changes to this base circuit:
R16 (SLOPE resistor) changed to 28K-Ohm
R17 (SYNCIN/RT resistor) changed to 36K-Ohm
C19 (SS capacitor) changed to 10nF
C13 (BST capacitor) changed to 2.2uF
But these only made marginal improvements, boosting the output to about 300W. While experimenting with the design in WEBbench, the recommended design calls for a higher value inductor and lower sense resistor, so we have ordered 6.8uH inductors and 1m-Ohm resistors to try out. But while we wait for these parts to arrive, is there any other parameters you recommending adjusting to improve the performance of the design? And specifically, what are probable causes for the pulse-skipping seen in the CCM_Fault.png image? Any insight you could lend would be appreciated.
