I am trying to build this circuit but I don't know how to test it. When I am measuring the voltage on the gate of high side mos is almost 12 volt like VCC. So to speak .. the boostrap circuit isn't working. Dou you have any ideas ?
Consider this typical circuit from this website:
When Lin is high and thus Q2 is 'on', the output is low and C2/C6 are near ground on the negative side. Vcc then charges the capacitor through diode D1. This provides a voltage source relative to the source of Q1.
When Hin goes high those charged capacitors are used to drive the gate of Q1 high. The charge on the capacitors will eventually be depleted,and Q1 will no longer be able to turn on fully. Some drivers contain a second UVLO for the high side switch, preventing damage which could occur from having the high side transistor partially turned on. The IR2101 does not appear to have that. See, for example, this application note.
So to use this, you should be switching both Lin and Hin actively at a reasonable frequency (typically in the kHz).
If you read the datasheet for the IR2101 then you can see that the bootstrap capacitor only increases Vb when there is a transition on the output of the external high side FET. So the high side boostrap uses positive feedback to increase the Gate drive voltage and can only work if there is a path to ground to allows the bootstrap capacitor to charge when the external high side driver is off.
So to test the unit you need to drive HIN and VB will ONLY increase if you have a load to allow the cap to charge when the high side switch is off. In other words you need some load to hold Vs lo.
Notice from the internal schematic that LIN has nothing to do with the bootstrap.