IR2101 self-turn off behavior

[HalmondD]

Hi, I designed a back 2 back mosfet circuit using IR2101 to drive it.


That back 2 back mosfet will connect to 8 half bridge circuit through the Vout net. Using IR2104 to drive it. Those 8 hb is floating at the time of testing.



The charge pump circuit run at 5Khz, and when I check the Voltage on bootstrap it's always high enough aroung ~10.5 to 11.5V, the Vcc is at 12V, and the logic input voltage is at 3.3V.

I double check the Vgs of IR2101, it stay at 0V when I try to turn on the back 2 back mosfet at 100V while the bootstrap is at 11.5V, but when I try to do it at 50V, the Vgs work normally.

After couple days of testing, we isolate the problem is between the connection of the back 2 back mosfet and the 8 half bridge, the charge pump and bootstrap circuit work perfectly, the problem only occure when we try to turn on the b2b while it is connected to the 8 hb mosfet. If it is Isolated from the 8 hb, the b2b work normally at any voltage even at 300V, but when I try to connect it to the 8 hb, it only work up to 80V, any higher than that and the b2b will not turn on at all.

The reason for the b2b mosfet not turning on because the Vgs of the IR2101 refuse to turn on, it will stay at 0V only for voltage higher than 80V any other than that the vgs turn on perfectly.

So we decided to isolate the b2b mosfet and the 8 haft bridge (hb), the Green line is a probe at point 1, and Yellow line is a probe at point 2, GND of the probe is also GND of the circuit. And the pink purple line is the minus between the Green and Yellow line.




How do I know the Vgs of the IR2101 self-turn off, I isolate the the b2b with the 8 hb completly, the voltage now at 100V, when the 2 is isolate the b2b work normally, when I try to manually bridge the b2b and 8 hb, the vgs on the ir2101 drop suddenly, key word suddenly, straigh down to 0.

If anybody has been working with the IR2101 and also having this problem please help me, I have been testing this circuit couple days and it is driving me crazy, I will accept any question and request for probing for further info on this ploblem, thanks in advance!