Your picture is of a IR2110 but you text is of a IR2112.
Most people don't under high side gate drivers.
1) The bottom side driver:Sits on ground and drives the bottom MOSFET. The output voltage is approximately 0 or 12 volts. It connects to the bottom MOSFET's G and S.
2)The top side driver: It does not sit in ground! It connects to the MOSFET's G and S. (some times there is a source resistor) It gets its power from +12V through a diode. Current goes through D1 and charges up C1,2 and through R5 load to ground. If R5 is missing the MOSFET driver can not function. (C1,2 will not charge up to 11.3V) The MOSFET must be off for 90% of the time so C1,2 can charge up!
3)To turn on the the MOSFET: The high side driver puts 11 volts across the gate to source. Now the FET turns on and the source goes up to 20 volts. (load supply) Notice the bottom of the high side drives also goes to 20 volts. (While the gate is at 31 volts the MOSFET has only 11 volts across G to S. ) You asked how can the MOSFET survive with high voltage on the gate. The FET only cares what is from G to S. It does not know that your meter is at ground.
4) The top side driver can not get power while the FET is on. The driver is living from power stored in C1,2. This power will run out after a while. The FET needs to be off 10% of the time to get power back into C1,2.
A high side driver is hard to trouble shoot even if you know how it works. Hope this helps you.
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