INN2603K SR Gate Driver Ratings
I am running an INN2603K with 4 synchronous rectifiers, corresponding to 4 different voltages. The DC input ranges from 100V to 375V. Start-up at any input voltage is no problem. However, when trying to recover from current-limiting mode, the circuit is unable to recover. It remains in a pulse-mode state (or in restart mode, but is never able to restart).
There are two interesting phenomena with this situation. The circuit is able to recover from current-limiting mode at 200V DC and below (no problems at all). However, input voltages ranging from 200V DC to 375V DC, the circuit struggles to recover from current-limiting mode, more noticeably as the voltage increases. Additionally, if the gate drive to 2 of the synchronous FETs is killed momentarily when trying to recover from current-limiting mode, the circuit IS able to recover independent of the input voltage.
Ultimately, is the SR gate drive circuit designed to drive 4 MOSFETs with C_iss ratings ranging from 700pF to 900pF at the drain-to-sources voltages seen by the FET in operation? The circuit works well, except when recovering from current-limiting mode.
Comments
Unfortunately I cannot provide all of this information. The transformer construction is sufficient because the circuit works at all other times, outside of current-limiting mode. The connection between the SR pin from the chip and the 4 gates is direct with no added resistance. Different synchronous FETs have produced different results. Certain FETs work well all the time, whereas others have had trouble even at start-up. There is no clear difference between the ones that do work and the ones that do not. I believe the FET design is at least part of the issue, but not sure exactly what in the design is the cause.
Regarding the waveforms, there are no clear waveforms. Every 2 seconds the chip pulses to try to recover (in current-limit mode), even when the load is removed. The pulses are non-distinct noisy waveforms, in the form of a pulse. For recovery, the load is reduced and then removed. The chip still has trouble recovering. Additionally, BPP voltage is above the clamping voltage of 6.4V during pulse mode. The voltage reaches about 8V before another auto-restart cycle.
The most unusual aspect of the problem is that the circuit only has trouble recovering at input voltages above 200V DC (exactly 200V DC). Between 100V - 200V DC, there are no issues at all.
At higher line voltages, the primary peak drain voltage due to the spike is much higher. Also for higher output voltages, the bias winding voltages are higher which could inject more than needed current to the BPP pin. You would want to probe these waveforms and compare them with normal operation waveforms. If you could also provide us with these waveforms or numbers then we could get some direction to think what could be the cause.
Dear mmie2600,
Can you please share the schematic, transformer document and waveforms during the abnormal operation.
By recovering from current limiting mode, What are you actually doing for it to recover? Are you reducing the load so that it goes back to constant voltage mode at the output?
PI-AP